14.3: Inheritance patterns are often more complex than predicted by simple Mendelian genetics.
1. Complete Dominance: dominance in which heterozygote and homozygote for the dominant allele are indistinguishable
2. Incomplete Dominance: type of dominance in which F1 hybrids have an appearance that is in-between that of the two parents.
3. Codominance: two alleles both affect the phenotype in separate, distinguishable ways
-ex: the human MN blood group
4. Relationship between Dominance and Phenotype: the dominant allele does not subdue the recessive allele; they don't physically interact at all.
-ex: In Mendel's study of pea plants, some were round (dominant allele: RR) and some peas were wrinkled (recessive allele: rr). The dominant allele codes of an enzyme converting unbranched starch in the seed to branched starch. The recessive allele codes for a defective form of this same enzyme resulting in an accumulation of unbranched starch. This leads to excess water entering the seed through osmosis; as the seed later dries, it wrinkles. Heterozygote (Rr) peas were round as well because the one dominant allele generates enough branched starch that no excess water enters the seed.
5. Multiple Alleles: when two or more different alleles exist for the same trait
-ex: ABO blood groups in humans, for instance, are determined by 3 alleles of a single gene: IA, IB, and i.
6. Pleiotropy: ability of a single gene to affect many different traits in an organism
-ex: in peas, the same gene codes for flower color (purple or white) and outer seed color (gray or white)
7. Polygenic Inheritance: two or more genes have an additive effect on a single character in the phenotype
-basically opposite of pleiotropy
-ex: at least three different separately inherited genes code for human skin color
8. Nature and Nurture: Environmental Impact on Phenotype: phenotype sometimes depends on environment as well as genotype
-ex: a tree's leaves vary in shape, size, and greenness depending on wind and sun exposure
14.4: Many human traits follow Mendelian patterns of inheritance
1. Family pedigree: information collected about a family's history of a particular trait assembled into a family tree
-helps calculate probability that a child will have a particular genotype or phenotype
-used especially when alleles in question lead to deadly or disabling diseases (cystic fibrosis)
This family pedigree is analyzing Dystonia, a neurological movement disorder.
2. Behavior of recessive alleles: when functioning for a genetic disorder, the allele either codes for a malfunctioning protein or no protein at all
-recessive disorder only shows up in recessive homozygous individuals
-heterozygote individuals considered a carrier because they carry one recessive allele and therefore have the ability to pass it along to their offspring
3. Dominantly Inherited Disorders: some human disorders are caused from dominant alleles but it is much less common and they are rarely lethal
-ex: some types of dwarfism (anchondroplasia)
-if dominant allele is lethal before maturation of the offspring, it will not be passed on to future generations because the offspring never had time to reproduce
-exception: Huntington's disease, which is a lethal degenerative disease of the nervous system, is caused by a dominant allele. However, phenotypic symptoms do not show up until age 35 to 45. Any children born to the affected parent has a 50% chance of inheriting the allele/disorder
4. Genetic testing can often be a highly controversial issue.
-parents can be tested to find out whether they are carriers of a disorder
-the amniotic fluid of a 14-16 week old uterus can be tested for disorders as well
-disease are now screened for routinely at birth
-ex: phenylketonuria, a mental retardation, can be screen for at birth and actually prevented by a special diet (most disorders can't be treated as an infant)
1. One gene coding for different traits in an organism is an example of:
c) multiple alleles
d) polygenic inheritance
2. A family pedigree can help answer which of the following questions?
a) What is the likelihood that my child will have a widows pea?
b) Is there a potential my child will have cystic fibrosis?
c) Will my child have friends?
d) Both a & b
3. A carrier of a disorder passed on through a recessive allele that is not affected physically but has the ability to pass it on must be:
a) homozygous dominant
c) homozygous recessive
d) trizygous recessive
Good luck on the quiz tomorrow!