Genetics Problems: Punnett Squares

Name: ______Date: ______Period:______

Genetics Problems: Punnett Squares

Instructions: Answers mean nothing in this assignment. SHOW YOUR WORK. Work should be on blank sheets of lined paper. Human eye color is usually, but not always, inherited as if brown eyes were due to a dominant factor and blue to the corresponding recessive. Assume that this is correct in questions 1-4.

1. A man with blue eyes marries a brown eyed woman whose mother had blue eyes. What proportion of the children would be expected to have blue eyes? (B- is brown) (bb is blue)

2. A brown eyed man marries a blue-eyed woman. The first child is blue-eyed. What is the man’s genotype? (B- is brown) (bb is blue)

3. Which is more likely, two brown-eyed parents producing a blue-eyed child or two blue-eyed parents producing a browned-eyed child? (B- is brown) (bb is blue)

4. A brown-eyed man marries a blue-eyed woman and they have eight children, all with brown eyes. A) Can you be sure whether the man is homozygous or heterozygous? B) Which is more likely? C) If the ninth child is blue-eyed, will that change your answer?

5. What offspring would be expected from mating (a) a roan cow with a roan bull? (b) a roan with a white? (c) a red with a white? rr is white, Rr is Roan, RR is Red. Roan refers to cows that have red coats with white blotches.

6. What would be the easiest way to determine whether a rose-combed male is homozygous or heterozygous? (R- Rose comb, rr single comb)

7. Which would be easier to get rid of in a flock of poultry, a recessive factor for single comb or a dominant factor for feathered legs?

8. In mice, the genotype yy is gray (agouti), Yy is yellow, and YY dies as a small embryo. What offspring would be expected form a mating between (a) a yellow and a gray? (b) between two yellows? (c) In which mating would you expect the larger litter size?

9. In humans the gene for ability to taste phenyl-thio-carbamide, A, is dominant to its allele for inability, a. Letting B and b stand for the brown- and blue-eyed alleles, what is the probability that (a) the first child of two parents, each AaBb, will be a blue eyed taster? (b) a blue-eyed non-taster? (c) What children would be expected from two parents of genotypes Aa Bb and aa bb? (d) What proportion of the children of two parents of genotypes Aa BB and aa bb would be expected to be brown-eyed tasters? (e) blue-eyed tasters?

10. In cocker spaniels the genotype A-B- is black, aa B- is silver, A- bb is red, and aa bb is lemon. A black cocker is mated to a lemon one and produces a lemon pup. If this black dog is mated to another of its own genotype what proportions of the different colors would be expected in the offspring?

11. In cattle, polled (hornless) is dominant to horned. (H-hornless, hh horned, rr is white, Rr is Roan, RR is Red). What proportion of the progeny of a roan, heterozygous polled bull and a roan, horned cow would be expected to be roan horned?

12. How many kinds of gametes can be produced by an individual of genotype AaBbCCddEeFF?

13. What proportion of the offspring of two parents, each of genotype AaBbCc, will be aabbcc?

14. What proportion of the offspring of the mating AaBbCc by AaBbCc would be expected to be homozygous for all three genes?

15. One hypothesis for the inheritance of handedness is that two genes are involved. L-produces left cerebral language dominance and ll right. C-causes the favored hand to be contralateral to the dominant hemisphere; cc produces ipsilateral (same side) handedness. According to this hypothesis, which of the following would be left handed: (a) C-L-, (b) C-ll, (c) ccL-, or (d) ccll?

16. Give an example of genotypes that would permit two left-handed parents to produce (a) only right-handed children. (b) only left-handed, (c) both right and left handed children.

17. In humans the allele D is necessary for a normal ear cochlea and allele E is necessary for a normal auditory nerve. In the absence of either of these genes the person is deaf. Show how (a) two normal parents can have a deaf child and (b) two deaf parents could produce only normal children.

18. Either the homozygous state of allele a or the heterozygous (or homozygous ) state of allele B results in retinitis pigmentosa, a form of blindness. Only the genotype A-bb is normal. A blind woman whose parents were both normal marries a man of genotype AaBb. What proportion of the children would be expected to be blind? (hint: Parents of blind woman have genotype of Aabb)

19. In poultry the genotype C-D- ii is colored: all other combinations are white. The Leghorn breed is CCDDII, White Wyandottes are cc DD ii, and white silkies are CC dd ii. What offspring would be expected from: (a) a white Silkie mated with a white Wyandotte? (b) a white Leghorn mated with a white silkie: (c) a Leghorn-Silkie hybrid backcrossed to a Silkie? (d) a Leghorn silkie hybrid mated with a Wyandotte?

20. In corn all three dominant factors, A, C, and R, are necessary for colored seeds. Genotypes A-C-R- are colored; all others are colorless. A colored plant is crossed with three tester plants with the following results:

With aa cc RR it produced 50% colored seeds

With aa CC rr it produced 25% colored seeds

With AA cc rr it produced 50% colored seeds

-  What is the plant’s genotype?

21. In snails the gene for right-hand coiling. R, is dominant to that for left-hand coiling, r. However, the direction of coiling is determined not by the genotype of the sail itself, but by the genotype of its mother. If there is a left-coiling snail that, when self-fertilized, produces only right-coiling offspring, what is the snail’s genotype?