Genetics. Spring 2001 First Test
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This test consists of 9 short answer questions (4 points each), 9 multiple choice questions (4 points each), and 2 problems (14 points each).
For the short answer questions, you must answer the question in the space provided. Make your answer clear, concise, and legible. There is partial credit on short answer questions.
For the multiple choice questions, choose the best answer from those available. Write your answer in the space provided. Only unambiguous answers written in the correct place will count. There is no partial credit on multiple choice questions.
For the problems, you may use a calculator, but make sure that you write out your calculations so that I can see what math you did to get to your answer. Make sure that you answer the questions that are asked clearly, concisely, and completely. Partial credit will be given for problems. However, a correct answer in which there is additional incorrect material will not receive full credit.
If you need clarification of a question or problem, raise your hand. I will clarify standard English, but I will not define genetics terms for you
Short answer questions. 4 points each.
1. You are looking into a microscope at a male horse cell that is in anaphase II.
In horses, 1N = 25. Please fill in the following.
The number of chromosomes in the cell =
The number of chromatids in the cell =
The number of chromosome sets in the cell =
The number of homologous pairs in the cell =
2. What's the difference between sex-limited and sex-influenced?
3. The gene controlling eye color in mice is X linked; the red allele is recessive to the black allele. A purebred red eyed male is crossed with purebred black eyed female. Please describe the phenotypes of the F1 and F2 generations resulting from this cross. Include the frequencies for each phenotypes.
4. What is dosage compensation and how is it achieved in mammals?
5. Define incomplete penetrance and variable expressivity. Make sure that your definitions distinguish the two concepts clearly.
6. Give 4 mechanisms of sex determination.
7. An individual has the following arrangement of alleles for the A/a, B/b, and C/c genes. The A/a and B/b genes are autosomal, linked and 20 m.u. apart. The C/c gene is autosomal but unlinked to A/a or B/b.
A b C
a 20 m.u B c
This individual makes gametes. What proportion of these gametes will have the genotype ABC? Show the math; you do not have calculate the actual number.
8. Define two different types of polygenic inheritance.
9. An individual has the following genotype: AaBbCCddEeFf. How many different gamete genotypes can this individual make for these genes? Show the math. Don't worry about actually figuring out the number.
Use the following information for questions 10 and 11.
In Spider monkeys, one gene controls tail length, another controls fur color. Purebred black, long tail female spider monkeys are crossed with purebred white, short tailed males. The following offspring are produced.
males 43 black long tailed
females 45 black medium length tails Answer 10
10. What are the rules of expression for the fur color and tail length genes?
A Fur color: The Black allele is dominant to the white allele.
Tail length: Long tail allele is dominant to short tail allele.
B. Fur color: The Black allele is dominant to the white allele.
Tail length: Long tail allele and short tail allele are codominant.
C. Fur color: The Black allele is dominant to the white allele.
Tail length: Long tail allele and short tail allele are incompletely dominant.
D. Fur color: The Black allele is recessive to the white allele.
Tail length: Long tail allele and short tail allele are incompletely dominant
E. Fur color: The Black allele is dominant to the white allele.
Tail length: Medium tail is dominant to short tail.
11. Which of the following describes the mode of transmission for these two genes?
A. Fur color: Autosomal Answer 11
Tail length: Autosomal
B. Fur color: X-linked
Tail length: Autosomal
C. Fur color: Autosomal
Tail length: X-linked
D. Fur color: X-linked
Tail length: X-linked
E. Could be more than one of the above. There is not enough data to draw a firm conclusion.
12. In guppies (fish), the tail length gene is on the seventh autosome. Males carrying the T allele develop long tails. Females carrying the T allele have short tails, as do males carrying only the t allele. The expression of the T allele is:
A. Sex-limited B. Sex-linked C. Sex-influenced
D. Dosage compensated E. Lyonized Answer 12
13. In Drosophila (fruit flies), males carrying the Abx- allele have an extra pair of wings and are sterile. The expression of the Abx- allele is an example of:
A. pleiotropy B. phenocopy C. epistasis
D. incomplete penetrance E. variable expressivity Answer 13
14. Tail length in house cats is controlled by two X-linked genes and two autosomal genes (one on the third autosome, the other on the eighth autosome). Each gene has multiple alleles that affect tail length independent of the effects of the other genes. This is an example of:
A. pleiotropy B. additive inheritance C. epistasis
D. sex-linked inheritance E. variable expressivity Answer 14
15. The R/r and T/t genes are 30 m.u. apart on the 18th autosome in humans. An individual with the genotype RrTt makes gametes. What proportion of the gametes will have the genotype Rt?
A. 0.5 B. 0.25 C. 0.3 D. 0.15
E. There is not enough information here to answer this question Answer 15
16. A gene controlling Blue/green color sight is on the second autosome; the allele causing blue green color blindness is recessive to the allele causing blue/green color sight.
The allele that causes progressive myeloencephalopathy (PME) is mitochondrial.
George has PME and has blue/green color sight. His wife Mary is blue/green color blind and does not have PME. What proportion of their kids will have PME and be blue/green color blind (at the same time).
A. 1/2 B. 1/4 C. 1/8
D. 1/16 E. 0 Answer 16
Use the following information for questions 17 and 18. The A/a and B/b genes are autosomal and unlinked. A purebred individual showing the A and B phenotypes is crossed with a purebred individual with the a and b phenotypes. The F1 individuals go on to make gametes.
17. What proportion of the gametes will have the genotype AB?
A. 50% B. 25% C. 15%
D. 7.5% E. None Answer 17
18. The F1 of the mating above are allowed to mate among themselves. What proportion of the F2 generation will be heterozygous for both genes?
A. 50% B. 25% C. 15%.
D. 7.5% E. None Answer 18
Problems. 14 points each.
Problem #1
In Morning Glories (a plant) a pure white flower only results when a plant is homozygous for recessive alleles of four different genes (= aabbccdd). The A/a and B/b genes are 10 map units apart on one autosome. C/c and D/d are 20 map units apart on a different autosome.
A plant homozygous for the A B c d alleles (red flowers) is crossed with a plant that is homozygous for the a b C D alleles (blue flowers) The offspring have purple flowers.
1. (4 points) Diagram the crosses given here, giving the genotypes of all individuals described above.
2. (4 points) Describe the rules of expression for flower color.
3. (6 points) The purple flowered plants are mated with each other. What proportion of the offspring of this mating will have white flowers? Show your calculations and explain briefly the reasons for coming to these conclusions.
Problem #2.
Purebred female Purebred male
black long furred, flop-eared bunny white short furred, straight-eared
Offspring
46 males, all black long furred flop-eared
45 females, all grey short furred, straight eared
The offspring are allowed to mate with each other to produce:
males
381 black long furred, flop-eared
19 white long furred, flop-eared
97 black long furred, straight-eared
3 black short furred, flop-eared
379 white short furred, straight-eared
21 black short furred, straight-eared
94 white short furred, flop-eared
6 white long furred, straight-eared
females
380 black long furred, flop-eared
20 grey long furred, flop-eared
96 black long furred, straight-eared
4 black short furred, flop-eared
382 grey short furred, straight-eared
17 black short furred, straight-eared
95 grey short furred, flop-eared
6 grey long furred, straight-eared
Please determine Rules of expression (3 points), mode of transmission (3 points) and linkage relationships (8 points) for the three genes involved in fur color, fur length, and ear shape. Draw a map and give map distances, where appropriate. Show all your calculations.