Tuesday, February 24, 2009

Chapter 24 Notes!

Unit 8: Mechanisms of Evolution
Chapter 24 The Origin of Species

What is a Species?
Macroevolution refers to the origin of new taxonomic groups.

Speciation is the process by which a new species arise.

There are many barriers that prevent members of different species from interbreeding these barriers can be broken down into two types – prezygotic barriers (those that prevent mating between species or hinder fertilization) and postzygotic barriers (those that prevent a fertilized egg from developing into a fertile adult.)

Examples of prezygotic barriers include:
1. Habitat isolation: – two species can live in the same geographic area, but not in the same habitat; this will prevent them form mating.
2. Behavioral Isolation: Some species use certain signals or types of behavior to attract mates, and these signals are unique to their species. Members of other species will not recognize them, which prevents them from mating
3. Temporal Isolation: Species may breed at different times of the day, different seasons, or different years, and this can prevent them from mating.
4. Mechanical Isolation: Species may be anatomically incompatible
5. Genetic Isolation: Even if the gamete of two species do meet, they might be unable to fuse to form a zygote.

Example of postzygotic barriers include:
1. Reduced Hybrid Vitality: When a zygote is formed, the fact that two species are genetically incompatible may cause development to cease.
2. Reduced Hybrid Fertility: Even if the two different species produce a viable offspring. Reproductive isolation is still occurring if the offspring are sterile and can’t reproduce.
3. Hybrid Breakdown: If the two different species produce offspring that are viable and fertile, these hybrids may mate to produce weak or sterile offspring.
Modes of Speciation
There are two main types of speciation-allopatric speciation, in which a population forms a new species because it is geographically isolated form the parent population, and sympatric speciation, in which a small part if a population becomes a new population without being geographically separated from the parent population.

Same geologic events or processes that can fragment a population include the emergence of a mountain range, the formation of a land bridge, or the evaporation of a large lake to produce several small lakes.

Small, newly isolated populations undergo allopatric speciation more frequently because they are more likely to have their gene pools significantly altered. Allopatric speciation has occurred when an individual from the new population us unable to mate successfully with an individual from the parent population.
ALLOPATRIC SPECIATION: THE SAME EVENT CAN AFFECT MANY LINAGES AT ONCE

One mechanism that can lead to the formation of a small new population within the parent population (sympatric speciation) in plant is the formation of autopolyploid plants through nondisjunction in meiosis. These plants have 4n chromosomes, instead of the normal 2n number, and they are unable to breed with members of the parent population—though they are still able to breed with other tetraploids.

Polyploid speciation occurs in animals, but it is not common. Instead, in animals, sympatric speciation can result from part of the population switching to a new habitat, food source, or other resource.

The punctutated equilibrium model states that species diverge in relatively quick spurts rather than slowly and gradually.

Adaptive radiation occurs when many new species arise from a single common ancestor.
Extra Notes:
While the biological species concept emphasizes the separateness of species from one another due to reproductive barriers, several other definitions emphasizes the unity within a species.
  • Morphological Species Concept: characterizes a species by body shape and other structural features
  • Ecological Species Concept: views a species in terms of it ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment.
  • Phylogenetic Species Concept: defines a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life

Allopolypoid: When two different species interbreed and produce hybrid offspring.

1. The largest unit within which gene flow can readily occur is
a. population
b. species
c. genus

2. Which of the following factors would not contribute to allopatric speciation?
a. Gene flow between the two populations is extensive.
b. The isolation populated is exposed to different selection pressures than the ancestral population.
c. A population becomes geographically isolated from the parents population.

3. Does polyploidy result in
a. a complete set of chromosomes
b. more than two complete sets of chromosomes
c. only two complete sets of chromosomes

Anwers: 1) B 2) A 3) B

Monday, February 23, 2009

Hardy-Weinberg Problems

Some practice problems!!!

1. In a population of 100 individuals 49% are of the NN blood type. What
percentage is expected to be MN assuming Hardy-Weinberg equilibrium?
A. 9%
B. 21%
C. 42%
D. 51%
E. insufficient information to answer question

answer: C

2. Attached ears is an autosomal recessive trait in humans. Assume that there are
400 people with attached ears in a population of 10000. How many individuals
would be expected to homozygous dominant?
A. 800
B. 100
C. 6400
D. 200
E. 10,000

answer: C

3. In a population that meets the H-W equilibrium assumptions, 81% of the
individuals are homozygous for a recessive gene. What percentage of the
individuals would be expected to be heterozygous for this gene in the next
generation?

answer: 81% homozygous recessive, 18% heterozygous

4. Coat color in a population of rabbits is controlled by three alleles. The c+ allele
codes for brown coat, the cch allele codes for chinchilla coloration, and the ch
allele codes for himalayan coloration. The dominance relationship is c+ > cch >
ch. Suppose that in a population of 100 rabbits there were 4 himalayans and the
frequency of the chinchilla allele is .20. What are the frequencies of the 3 alleles?

answer: the 4 himalayan are homozygous recessive; r2 = 4/100 = .04, so r = .2

a. How many homozygous dominant (c+ c+) individuals are in the population?

answer: 36 homozygous dominant individuals

b. How many heterozygous (c+ ch) individuals?

answer: 24 heterozygous individuals

5. A farmer bought a herd of 600 sheep, taken from a freely breeding population, and later found that 150 of the animals had an economically undesirable feature, crinkly-hair, caused by the recessive allele cr.

A.What is the frequency of this undesirable allele in the herd?

answer: 0.5

B.What proportion of the herd is likely to be heterozygous?

answer: 50%

C.The owner then separates all those animals showing crinkly-hair and sends them for slaughter.He allows the remaining animals to breed freely.What proportion of the next generation of lambs would be expected to show crinkly hair?

answer: 1/9

6. If, in a sample of people from Birmingham, 22% were found to be of blood group N, what, approximately, would be the expected percentages of the M and MN groups?

answer: M 28.2%, MN 49.8%

7. The alleles for red and white coat color in cattle show absence of dominance, the heterozygote being roan.

A.In a freely breeding herd of 1000 head how many would you expect to be of each coat color if the allele for white coat has a frequency of 0.4?

answer: Red: 36%, Roan 48%, White 16%

B.If all the white cattle were sold for slaughter and the red and roan animals were allowed to breed freely, about what percentage of the offspring would be expected to be white?

answer: 8.2%

8. A recessive lethal gene in chickens causes circulatory failure and death of the embryo at 70 hours.A commercial hatchery finds that a hatching failure due to this gene of greater than 4% is unacceptable.What is the upper limit for the frequency of this allele in the breeding population of fowls that is acceptable to the hatchery managers?

answer: 0.2

9. In a sample of 2400 births at a maternity hospital, six babies died shortly after birth from the effects of a recessive gene (co) for colonic obstruction.

A.What is the frequency of this gene in the population?

answer: 0.5

B.What proportion of the population is heterozygous and what proportion is homozygous for the normal allele?

answer: Heterozygous: 9.5%; Homozygous normal: 90.25%

10. A rancher decided to raise cattle in an isolated valley and bought 1000 head which he transported to the valley to establish a randomly mating population.When released, the animals consisted of 130 white-coated beasts, 330 red, and 540 roan.

A.Does this represent a population in equilibrium?

answer: No

B.What will be the proportions of coat color in the next generation?

answer: Red 36%, roan 48%, white 16%

C.Is this second generation in equilibrium?

answer: Yes

A Question to Ponder

Please reply on the blog: (optional, but those that do will benefit)

Read the following statement. Then, based on your knowledge of cell biology,genetics
and evolution,decide to agree or disagree with the statement. Whichever you decide,
write a short paragraph that provides solid evidence defending your choice.

“When you think about sexual reproduction,it makes no sense. After all,evolution
selects for organisms that are best fit. In a population of sexually reproducing organisms,
a mutant that reproduced asexually would increase its representation more quickly than
the wild type,that is,it would have a higher fitness. So we should expect asexual
reproduction to be much more widespread among eukaryotic species than it is.”


Mrs. Lyon
Thought that I would give you the web link for the Hardy-Weinberg problem. This concept is so important as the AP test will most likely include evolution as part of an FRQ. Important to understand causes of microevolution as well as the conditions for H-W.

http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6-OSU.swf

The week at a glance: As we finish microevolution, we will move into macroevolution. Anatomy & Physiology is right around the corner!

Tues: Chapter 24 notes and Ch. 24 vocab quiz
Wed: Chapter 24 notes
Thurs: all school community service
Friday: Ch. 24 quiz; Unit 8 essay; 26-27 take home; ch. 26 notes

Mrs. Lyon

Saturday, February 21, 2009

The Rest of Chapter 23-The Evolution of Populations

The Hardy-Weinberg Equation can be used to determine or predict the allelic frequencies that exist in populations. In order for a population to be in Hardy-Weinberg equilibrium, it must meet all of these criteria:

1. It must be a very large population in size. If a population is small, a change in the gene pool due to chance will have an inordinate effect on the gene frequencies of a population.
EXAMPLE: If you have a small population of purple (dominant) and pink (recessive) flowers and there is a hurricane, all of the population that shows the recessive trait may die and completely alter the gene frequencies so that there are far fewer pink flowers than there usually would have been.

2. There must be no migration in a population. Gene flow, which is the transfer of alleles between populations, cannot occur because that would alter gene frequencies.
EXAMPLE: If a few deer that usually have large antlers wander into a population of deer that have short antlers and start to breed, over time, the population could change dramatically.
3. There can be no mutations. Mutations can change one allele into another, thus altering the gene pool.
EXAMPLE: One ground squirrel has a mutation that gives him more storage space in his cheeks, and he reproduces and passes the mutation onto other ground squirrels. Eventually, a large portion of the population has more cheek storage space and the population is much different than it was originally.

4. Mating must occur randomly. If individuals mate only with other individuals of a certain genotype, this does not meet the criteria of a random mixing of genes.
EXAMPLE: Lionesses look for mates with larger manes who are therefore stronger and better fit to survive. Genes do not mix randomly, so eventually, because more females mate with large-maned males, more lions have big manes.

5. Natural selection may not be taking place. This would alter gene frequencies and cause a deviation from Hardy-Weinberg equilibrium.
EXAMPLE: Longer necked giraffes can reach the highest leaves and therefore have a better chance of surviving. The long necked giraffes that survive give birth to more long necked giraffes.

***Unless a population is being carefully contained and monitored, it is basically impossible for all of these situations to hold true naturally. There is often migration and mutations, natural selection is always occurring, and mating is rarely random. This is why Hardy-Weinberg equations are used to find out how a population changes. The first set of data obtained provides a baseline and the next set shows that the population is evolving (it is rare to get the same, or nearly the same, data as the baseline).
***Populations that deviate from the Hardy-Weinberg equilibrium are, therefore, said to be evolving.

Microevolution can be defined as a generation to generation change in allele frequency in a population. The main causes of microevolution are genetic drift, natural selection, gene flow, and mutation.
*Not to be confused with macroevolution: evolutionary change above the species level, including the origin of a new group of organisms or a shift in the broad pattern of evolutionary change over a long period of time.

1. Genetic Drift: refers to a change in a population's allele frequencies due to chance.
A) The Bottleneck Effect: occurs when a natural disaster or some other event causes a drastic reduction in the size of a population, which in turn causes genetic drift. Bottlenecking usually reduces the genetic variability in a population, since some alleles are lost from the gene pool.
EXAMPLE: Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.
B) Founder Effect: occurs when a few members of a population colonize an isolated location-the smaller the number of founders, the more limited the variability of the genes in the population.
EXAMPLE: The Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency.
2. Natural Selection: refers to the differing reproductive success of individuals in a population. The individuals best suited to their environment will survive to reproduce and to pass on their alleles to the next generation.
A) Stabilizing Selection: favors intermediate variants by selecting against extreme phenotypes. The trend is toward reduced phenotypic variation and a greater prevalence of phenotypes best suited to relatively stable environments:
EXAMPLE: Birth weight. Babies of low birth weights generally have a lower chance of surviving (now with modern medical technology this actually isn't really the case). Babies with high birth weights are much harder and more dangerous to deliver. Average sized babies are the easiest to give birth to and have the best chance of survival.

B) Directional Selection: favors variants of one extreme. It shifts the frequency curve for phenotypic variants in one direction toward rare variants which deviate from the average of that trait.
EXAMPLE: This is most common when members of a species migrate to a new habitat with different environmental conditions or during periods of environmental change.

C) Diversifying (aka Disruptive) Selection: opposite phenotypic extremes are favored over intermediate phenotypes. This occurs when environmental conditions are variable in such a way that extreme phenotypes are favored.
EXAMPLE: A species of butterfly with characteristics between two noxious model species gain no advantage from their mimicry.

3. Gene Flow: refers to the genetic exchange due to the migration of individuals or gametes between populations.

4. Mutations: refers to a change in an organism's DNA. This can alter the gene pool of a population by changing one allele into another.

Genetic Variation, substrate for natural selection.

Genetic Variation exists naturally in populations. Quantitative characteristics, such as height in humans, vary in a continuum in a population.

A population is said to be polymorphic for a character if this character exists in two or more discrete forms in the population-for example, if a plant bears two different kinds of flowers in population. Geographic variation refers to differences in gene pools between populations or parts of a population.

A cline is one type of geographical variation that is a graded change in some trait along a geographic transect.
EXAMPLE: As altitude increases, the size of plants decrease.

Two processes contribute to the variation in the gene pool of a population, one is mutation and the other is sexual recombination.

Since mutations in some somatic cells disappear when the individual dies, only mutations in gametes are passed to offspring.

Most of the genetic differences that exist in a population are due to the genetic recombination of alleles that already exist in a population.

Genetic recombination is the most important factor in producing variability that occurs in each generation of humans. It can be supported by the existence of sex, bacterial conjugation, and the exchange of chromosome regions in meiosis.

***Quick Review
-Genetic recombination is the production of offspring with combinations of traits that differ from those found in either parent.
+If you want to brush up on this subject, reference Chapter 15.
Factors that contribute to the preservation of genetic variation in a population are diploidy (the condition of being diploid, or having two sets of chromosomes), and balanced polymorphism. The fact that most eukaryotes are diploid (like humans), means that they are capable of hiding genetic variation (recessive alleles) from selection. Balanced polymorphism refers to the ability of natural selection to keep stable the frequencies of two or more phenotypes in a population.

***Quick Review:
-Humans are always diploid, however we do have haploid cells (eggs and sperm).
-Fungi and some protists and algae have a diploid zygote. Meiosis occurs to produce haploid cells, and the haploid cells then divide by mitosis to give a multicellular haploid organism (fungus is a multicellular haploid most of its life).
-In plants and some algae, alternation of generations occurs which includes both a multicellular haploid and diploid stage in the life cycle.
+If you don't remember this and want to brush up, reference Chapter 13.

Individuals with heterozygote advantage are heterozygous at a certain locus, and this confers upon them an advantage that enables them to better survive.
EXAMPLE: Sickle Cell Anemia. People who do not have Sickle Cell Anemia but are carriers are resistant to Malaria.
Practice Questions:
1) Most copies of harmful recessive alleles in a population are carried by individuals that are A) heterozygous for the allele. B) polymorphic. C) haploid. D) homozygous for the allele. E) afflicted with the disorder caused by the allele.

2) All of the following are criteria for maintaining a Hardy-Weinberg equilibrium involving two alleles except A) gene flow from other populations must be zero. B) there should be no natural selection. C) the frequency of all genotypes must be equal. D) matings must be random. E) populations must be large.

3) What is the most reasonable conclusion that can be drawn from the fact that the frequency of the recessive trait (aa) has not changed over time? A) There has been a high rate of mutation of allele A to allele a. B) The population is undergoing genetic drift. C) There has been sexual selection favoring allele a. D) The two phenotypes are about equally adaptive under laboratory conditions. E) The genotype AA is lethal.

4) What effect do sexual processes (meiosis and fertilization) have on the allelic frequencies in a population? A) They tend to increase the frequencies of deleterious alleles and decrease the frequencies of advantageous ones. B) They tend to selectively combine favorable alleles into the same zygote but do not change allelic frequencies. C) They tend to reduce the frequencies of deleterious alleles and increase the frequencies of advantageous ones. D) They tend to increase the frequency of new alleles and decrease the frequency of old ones.

5) Which of the following is the unit of evolution? In other words, which of the following can evolve in the Darwinian sense? A) species B) gene C) chromosome D) individual E) population

ANSWERS: 1) A; 2) C; 3) D; 4) E; 5) E

****Here are a few websites where you can practice some Hardy-Weinberg problems:
A Little Background Info...:
The Hardy-Weinberg equation is named after H.G. Hardy (left) and Wilhelm Weinberg (right). To learn more about these two men and their equation, go to either of these sites:
(Hardy)
(Weinberg)


Remember!:
Monday- Hardy-Weinberg Worksheet Due
Two Chapter 23 Quizzes
Tuesday- Chapter 24 Vocab Quiz
Wednesday-
Thursday- Community Day (no class)
Friday- Chapter 24 Quiz
Lab 8 Essay
HAVE A WONDERFUL REST OF THE WEEKEND!!!!

Friday, February 20, 2009

Beginning Chapter 23 Notes

Alright girls, today we fixed the activotes, took a quiz and started on the notes for chapter 23.
Don't forget that chapter 24 vocabulary is due tomorrow!

Chapter 23 Notes:
The Evolution of Populations
The Evolution of Populations: Population Genetics
  • Natural selection acts on individuals
    • Their relative fitness determines if they will survive to reproduce
  • Evolution acts on populations
    Population is the unit of evolution
    • A species is a group of populations of individuals that can interbreed successfully and produce a viable offspring. Populations of the same species may be geographically isolated and only exchange genetic material rarely
    • The gene pool is the total aggregate of genes in a population at any one time
    • Made up of all the alleles at all loci in the members of the population
    • In diploid species, each individual has two alleles, and it may be either heterozygous or homozygous
    • If all members of a population are homozygous for the same copy of an allele, the allele is said to be fixed
    • The Hardy-Weinberg theory is used to describe a population that is not evolving
    The original proportion of genotypes in a population remains constant if • Population size is large • Random mating is occurring • No mutations • No genes are introduced or lost • No selection occurs
    • All genotypes can survive and reproduce equally well
    • States that the frequencies of alleles and genes in a population’s gene pool will remain constant over the course of generations unless they are acted upon by forces other than Mendelian segregation and the recombination of alleles.
  • Hardy-Weinberg Equilibrium
    • The situation in which the allele frequencies within a population are not changing
    • Allele Frequency Equation:
    Allele Frequency:
    p + q = 1 (p is dominant, q is recessive)
    Hardy-Weinberg Equation:
    Genotype Frequency:
    p2 + 2pq + q2 = 1 (p2 is homozygous dominant, 2pq is heterozygous and q2 is homozygous recessive)
Here are some extra notes from the book:
• Mutation and sexual reproduction produce the genetic variation that makes evolution possible.
• Genetic variation includes variation among individuals within a population in discrete and quantitative characters, as well as geogrphaic variation between polymers.
• New alleles ultimately originate by mutation. Most mutations are harmful or have no effect, but a few may be beneficial.
• In sexually reproducing organisms, most of the genetic differences among individuals reslt from crossing over, the independent assortment of chromosomes, and fertilization.
The Hardy-Weinberg equation can be used to test whether a population is evolving.
• A population, a localized group of organisms belonging to one species, is united by its gene pool, the aggregate of all the alleles in the population.
• The Hardy-Weinberg principle states that the allele and genotype frequencies of a population will remain constant if the population is large, mating is random, mutation is negligible, there is no gene flow, and there is no natural selection. For such a population if p and q represent the frequencies of the only two possible alleles at a particular locus, then p2 is the frequency of one kind of homozygote, q2 is the frequency of the other kind of homozygote, and 2pq is the frequency of the heterozygous genotype.


Sample Hardy-Weinberg problems: (answers are given in red)
  1. If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous(Ss) for the sickle-cell gene?
    9% =.09 = ss = q2
    s = q = Square root of .09 = .3

    p = 1 - .3 = .7
    2pq = 2 (.7 x .3) = .42 = 42% of the population are heterozygotes (carriers)
2. If 98 out of 200 individuals in a population express the recessive phenotype, what percent of the population would you predict would be heterozygotes?

(a) I have given you information on the frequency of the homozygous recessive (or q2). So start by determining q2 and then solving for q.

q2 = (98/200) = 0.49 (or 49%)

q = square root of 0.49 = 0.7 (70%)

(b) Now that you have q, you can solve for p. Remember there are only two alleles in the population, so if you add the frequency of the two alleles, you have accounted for all possibilities and it must equal 1. So p + q = 1.

p = 1-q

p = 1 - 0.7 = 0.3 (30%)

(c) Now what is the formula for heterozygotes? Think back to the Hardy-Weinberg equation -- it is dealing with the genotypes of individuals in the population.

p2 + 2pq + q2 = 1

frequency of homozygous dominant + frequency of heterozygotes + frequency of homozygous recessive = 1

so.....2pq = frequency of heterozygotes

frequency of heterozygotes = 2 (0.3)(0.7) = 0.42 or 42%

(d) Now that you have figured out the % of heterozygotes, can you figure out the % of homozygous dominant? Does the % of homozygous dominant, heterozygotes and homozygous recessive individuals add up to 100%? If not, you have made an error. Those are the only three genotypes possible with only two alleles and a simple dominant and recessive relationship.

p2 = (0.3)(0.3) = 0.09 (or 9%)

p2 + 2pq + q2 = 1

0.09 + 0.42 + 0.49 = 1.0

3. Your original population of 200 was hit by a tidal wave and 100 organisms were wiped out, leaving 36 homozygous recessive out of the 100 survivors. If we assume that all individuals were equally likely to be wiped out, how did the tidal wave affect the predicted frequencies of the alleles in the population?

Again, start with the frequency you know -- homozygous recessive. Follow the same step-by-step procedure as above.

What is the frequency of homozygous recessive?

q2 = (36/100) = 0.36

q = square root of 0.36 = 0.6

What is the predicted frequency of heterozygotes?

frequency of heterozygotes = 2pq

p = 1 - 0.6 = 0.4

frequency of heterozygotes = 2 (0.4)(0.6) = 0.48

What is the predicted frequency of homozygous dominant?

p2 = (0.4)(0.4) = 0.16

Double check:

p2 + 2pq + q2 = 1

0.16 + 0.48 + 0.36 = 1.0

Given that the allele frequencies did change as the result of the tidal wave, we would say that microevolution has occurred. What do we call the phenomenon that caused this evolution?

the drastic reduction in size of a population due to some chance event is called a bottleneck event - particularly when the original gene pool (allele frequencies) is no longer represented in the surviving population

since there is now a small population, chances are likely that it will be subjected to genetic drift and continue to shift away from the original allele frequency (pre-tidal wave)


Multiple Choice Questions:

  1. A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equidlibrium, what proportion of hte flies carry both A1 and A2?
    a) .7
    b) .49
    c) .21
    d) .42
    e) .09
  2. There are 40 individuals in population 1, all of which have genotype A1A1, and there are 25 individuals in population 2, all of genotype A2A2. Assume that these populations are located far from one another and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is mostly likely an example of
    a) genetic drift
    b) gene flow
    c) disruptive selection
    d) discrete variation
    e) directional seletion
  3. Natural selection changes allele frequencies because some _______________ survive and reproduce more successfully than others.
    a) alleles
    b) loci
    c) gene pools
    d) species
    e) individuals



Answers:
1. d
2. a
3. e

Wednesday, February 18, 2009

Wrapping up Chapter 22...

Well my fellow classmates of Biology in B and C block, here's the agenda for tonight's blog:
Let's finish up the chapter 22 notes and then study a little for our 22 quiz, shall we?

CHAPTER 22: Descent with Modification: A Darwinian Way of Life CONTINUED

-Homology: related species share characteristics; but this does NOT necessarily mean these characteristics share t
he same function.
-Homologous Structures are anatomical signs of evolution. If you look at the forelimbs of humans, cats, whales, and bats, they are all made of basically the same bones. Therefore, they all share a common ancestry. However, they use these limbs for all different things: lifting, walking, swimming, and flying.
-some homologous structures can only be seen in the embryo form of organisms. For example, ALL vertebrate embryos (including humans) have a tail behind the anus... these are called embryological homologies
-another type of homology are molecular homologies: occurring when organisms share characteristics on the molecular level (ex: use the same method for reproducing DNA or other cellular processes)
-some structures passed down from ancestors are no longer used by the present species-- these are vestigial structures
-vestigial structures can be great clues to tracking down the ancestry of a given organism. for example, some snake skeletons contain remnants of the pelvis and leg bones of their walking ancestors
-animals sharing a common ancestor may develop homologies that their ancestors did not have. for example, all tetrapods today have the same limb bone structure, but their ancestors do not.
-evolutionary tree: used to represent the pattern of descent from common ancestors and the resulting homologies





-Convergent Evolution: organisms evolve independently from different ancestors, but they adapt to similar environments in similar ways. They, therefore, share features that are analogous: they serve the same purpose.
-biogeography, the geographic distribution of species, also results in evolution. As continents drift apart it isolates populations often resulting in new species through adaptation and genetic drift. (a species only found in a certain area is called an endemic species-- these species are more prone to extinction)
-Linnaeus, known as the father of taxonomy, the naming and classifying of organisms, developed the system of binomial nomenclature still used today. He adopted a system for grouping species into categories and ranking the categories into a hierarchy.

Alrighty folks, that seems to be the end of Chapter 22. C Block didn't make it to any notes on 23, so that's all I've got. Here's a short review to help with the Chapter 22 Quiz manana:

1. If structures on several organisms share basic function but not ancestry, are they homologous or analogous?
2. According to Charles Darwin's theories on evolution, what is the result of natural selection?
3. __________ is the study of fossils.
4. Was Lamark's theory on evolution (characteristics acquired during an organisms lifetime can be passed on to the next generation) proved correct or incorrect?
5. Homologies that are not usually seen during adulthood are called ________ ________.

Answers:
1. analogous
2. the adaptation of a population to its environment
3. Paleontology
4. incorrect
5. embryonic homologies

Night night everyone. Good luck tomorrow.

Article on Paleontology in L.A.

I found an article about some fossils and bones found just outside of L.A. I'm not talking like one fossil of a fish I mean lots of animals like mammoths and saber-toothed cats. I thought I'd post it since ch 22 had a paragraph on fossils and it does relate to evolution. There are pictures, too. Enjoy.
http://news.aol.com/article/fossils-found-near-la-brea-tar-pits/347859

Saturday, February 14, 2009

Begining of Unit 8

Hey ladies, I hope everyone had a great 5 day weekend! Don't forget that we have a chapter 23 vocab quiz tomorrow and the gel electrophoresis lab is due tomorrow.


Chapter 22: Descent with Modification (A Darwinian View of Life)

Darwin Introduces a Revolutionary Theory

Evolution is defined as a change in the genetic make up of a population that enhance organisms' ability to survive and reproduce . It is also the change in allelic frequencies in a population.

Natural Selection: a population can change over generations if individuals that possesses certain heritable traits leave more offspring than other individuals. It only involves heritable traits.

Evolutionary Adaption: an accumulation of inherited characteristics that enhance organisms ability to survive and reproduce in specific environments





Section 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species

Many scientists in the 1700s believed that organisms experienced adaptations to their environments and believed that a Creator had designed each species for a specific purpose. On of these scientists was Carolus Linnaeus who founded taxonomy. Taxonomy is a branch of biology that focuses on the naming and classification of organisms. Linnaeus used a binomial system to categorize and name organisms. Organisms are classified by their genus and species.


To understand how animals have evolved over time paleontologists study fossils. Fossils are the remains or impressions of plans or animals in sedimentary rock. The study of fossils gives us a glimpse of organisms that populated the Earth at the time a certain layer of sedimentary rock formed. Georges Cuvier, the scientist who developed paleontology opposed the idea of gradual evolution and instead advocated catastrophism. Catastrophism is the theory that each layer of sedimentary rock represents a catastrophe that wiped out most of the species living at that time.


In contrast to catastrophism other scientists accepted the theory of gradualism-- the idea that profound change can take place through the cumulative effect of slow, continuous processes. Another scientist Charles Leyell took the theory of gradualism and formed it into a theory known as uniformitarianism. Uniformitarianism states that the same geological processes that occurred in history are operating at the same rate today and have not changed over the course of history.

Jean Baptiste Lamark published a theory of evolution that was commonly accepted before Charles Darwin's theory of natural selection. Lamark's theory consisted of two principles. The first principle was use and duse or the idea that parts of the body that are extensively used become larger and stronger while others deteriorate. The second principle is inheritance of acquired characteristics. This means that an organisms could pass modifications from use and duse to its offspring.


Section 22.2: In The Origin of Species, Darwin proposed that species change through natural selection

Charles Darwin's voyage on the HMS Beagle was the impetus for the development of his theory of evolution. He spend most of his time during this voyage on the shore collecting and observing thousands of South American animals and plants. This expedition sparked Darwin's interest in the geographic distribution of species. When the Beagle stopped at the Galapagos islands Darwin was fascinated by the unique birds and other species and how some species lived on 2 or 3 islands while others lived on one. Below is a picture of a blue footed booby and a frigate.

Within a decade of its publication Dariwn's book on his theory of natural selection had convinced most biologists that biological discovery was the result of evolution. Darwin had developed two main ideas: evolution explains life's diversity and that natural selection is a cause of adaptive evolution. In the beginning of his book The Origin of Species, Darwin referred to evolution as descent with modification--the idea that all living organisms are related by descent by a common unknown ancestor in the past.

Darwin's Theories:

1) Natural selection is the result of reproductive success as a result of "survival of the fittest"


2) The process of natural selection happens through the interactions between organisms and their environment that causes variations in the genotype of that population


3) Natural Selection = an organisms' adaption to its environment


Darwin derived a piece of his theory from the process of selective breeding of domesticated plants and animals. The process of breeding animals or plants to possess desired traits is called artificial selection. As a result of this humans have been able to bred animals or plants that bair little resemblance to their wild ancestors.
Multiple Choice Questions:
1) ____ stated that species evolved after a catastrophe when the species before it was mostly destroyed.
a. catastrophism
b. catabolism
c. gradualism
d. dissent with modification
2) True or False, Lamark's theory was never accepted by biologists before Charles Darwin's theory of evolution.
3) ___ is a geological theory that states that profound changes in the earth's features happen during slow, continuous processes.
a. uniformitarianism
b. gradualism
c. evolutionary adaption
d. paleontology
Answers: 1) A 2) False 3) A






















Friday, February 13, 2009

Man appears free of HIV after stem cell transplant

Hope it's ok that I'm posting this. I was stumbling and I found this article. I thought it was interesting since we just finished learning about HIV and such.

cnn health

Wednesday, February 11, 2009

We Ran GELS Today... :)

Ello ladies. Today was actually a really fun day... we started the gel electrophoresis lab and basically just hung out.

According to the very nifty iGoogle web definition, gel electrophoresis is a technique used to separate molecules based on size and/or charge. To separate molecules of DNA, we rely on the negative charge of DNA to pull it toward the positive electrode. The agarose gel allows smaller (shorter) lengths of DNA to travel more quickly than longer pieces of DNA.

In case memorizing that definition isn't  looking to appealing, you could try either of these two sites for more help understand gel electrophoresis:

This site basically walks you through the history of it (who founded this technique, why, etc.). You can play a series of short animations as you read. Click on the link below.

This is just a little helpful video I found via my video god aka youtube:

Alrighty kids, remember we have a vocab quiz tomorrow over chapter 22.

In the interest of keeping things exciting, I've decided to create a new sort of matching thing... Match the word with its interesting fact (no these aren't the definitions but just interesting things I've found; hopefully you can apply your knowledge of the definition in assessing these facts).

1. Homology
2. Endemic Species
3. Evolution
4. Gradualism
5. Vestigial Organs
6. Taxonomy
7. Natural Selection
8. Homologous Structures

a] Most humans are born with two eyes. Lindsey is born with one eye. This mutation hinders her ability to see a predator approaching, and she, therefore, is less likely to survive and reproduce. This scenario is an example of ______________.

b] This type of species is more prone to extinction.

c] A bat wing, cat paw/arm, and human arm/hand when compared to one another are examples of ______________.

d] The "__________ of dance" is a funny video on youtube showing how style of dancing has changed over the years.

e] This word is derived from ancient Greek meaning 'to agree.'

f] If you have no idea what you want to do when you get older, but you really like to name things, enter the field of _____________.

g] The top ten useless limbs are: 10) wings on flightless birds 9) hind leg bones in whales 8) erector pili and body hair 7) the human tailbone 6) the "blind fish," astyanax mexicanus', eyes 5) wisdom teeth in humans 4) the sexual organs of dandelions 3) fake sex in virgin whiptail lizards 2) male breast tissue and nipples AND 1) the human appendix. All of these are prime examples of ______________.

h] Lindsey had a child with seven eyes. There was no steady evolution leading to this sudden change in biological features. This mysterious case goes against the idea of _______________.


...SREWSNA
8)C 7)A 6)F 5)G 4)H 3)D 2)B 1)E 

Good luck on the rest of the lab/the quiz. Tomorrow is the last day of the week and then FIVE DAY WEEKEND, so let's all get 100% on the quiz and relax for a few days, eh?







Tuesday, February 10, 2009

Diversity Day

Hey girls. Today was Diversity Day, so no class. Don't forget that tomorrow we have a vocab check for chapters 22 and 23.

Hope we all had fun, ate some good food and learned something!

Sunday, February 1, 2009

Mock AP Review Questions

Hey ladies! I thought I'd post some multiple choice questions to help everyone study. Good luck! ;)

1) Transpiration in plants requires all of the following EXCEPT:
a) cohesion of water molecules
b) active transport of water molecules in the xylem
c) capillary action of water in the xylem
d) root pressure
e) evaporation of water

2) A salmon swims hundreds of miles to spawn where it was hatched. This is an example of:
a) classical conditioning
b) habituation
c) imprinting
d) operant conditioning
e) fixed action pattern

3) The role of oxygen in aerobic respiration is:
a) the final hydrogen acceptor in the electron transport chain
b) in glycolysis
c) in the Kreb's cycle
d) exactly the same as a cytochrome
e) to reduce NAD to NAD+

4) Which of the following is NOT caused by a mutation in a gene?
a) cystic fibrosis
b) hemopilia
c) Huntington's disease
d) Tay-Sachs disease
e) Klinefelter's Syndrome


5) The frequency of a crossing-over even occuring between any two linked genes is:
a) proportional to the distance between them
b) greater if the genes are sex-linked
c) higher if they are dominant and lower if they are recessive
d) higher if the genes are in a male
e) higher if the genes are on sepereate chromosomes

6) A species is defined in terms of:
a) geographic isolation
b) reproductive isolation
c) common ancestry
d) location
e) analogous structures

7) Which most accurately describes which way electrons flow in an active mitochondrion?
a) electron transport chain --> Krebs cycle--> ATP
b) glycolysis--> Krebs cycle-->electron transport chain
c) pyruvate--> Krebs cycle--> electron transport chain
d) Krebs cycle--> electron transport chain--> oxygen
e) All of the above are correct.

8) Polymerase chain reaction would be carried out to accomplish which of the following?
a) to prevent a virus from replicating
b) to amplify a region of DNA
c) to identify the location of a point mutagen in a genome
d) to identify a chromosome mutation
e) to prepare a specimen of DNA for X-ray diffraction

9) In an operon, the operator is the binding site for the:
a) promoter
b) regulator gene
c) repressor
d) RNA polymerase
e) inducer

10) A plant cell is placed into pure water. Which of the following will occur?
a) water will flow into the cell because the water potential inside the cell is higher than it is outside the cell
b) water will flow into the cell because teh water potential inside the cell is lower than it is outisde the cell
c) water will flow out of the cell because the water potential inside the cell is lower than it is outside the cell
d) water will flow out of the cell because the water potential inside the cell is higher than it is outside the cell
e) water will not flow into our out of the cell because the cell wall prevents water from diffusing in or out.


ANSWERS:

1.B 2.C 3. A 4.E 5.A 6.B 7.B 8.B 9. C 10. B

(These Q's are from Barron's AP exam prep book. I don't really recommend it because we have all the notes but the multiple choice questions are good)

P.S. I read the book "My Sister's Keeper" which was recommended below and it was really good. I think a lot of people would like it- if anyone wants to borrow it I have a copy.