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

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

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