GENETICS PROBLEMS

These are some ADDITIONAL PROBLEMS for you to practice with; these do *not* represent the assignment to be turned in.

SHOW ALL WORK!

1. A brown mink crossed with a silver blue mink produced all brown offspring. When these F1 mink  were crossed among themselves they produced 47 brown animals and 15 silverblue animals. Which of these characters is the dominant allele for this gene?

 

2. How many of the brown mink (see problem 1) in the F2 generation would be expected to be homozygous? (state in fraction or %) 

 

3. What % (or fraction) of the silverblue F2 animals (see problem 2) would be homozygous? 

 

4. How could you determine which of the brown mink in the F2 generation of problem 2 were homozygous and which were heterozygous? 

 

5. In chickens, rose comb is dependent upon a dominant gene (R), single comb upon its recessive allele (r). Birds of the Wyandotte breed are required to have rose combs. In certain strains of Wyandottes, however, single-combed birds occasionally appear. Why is this?

 

6. How can a breeder of Wyandottes eliminate the single-comb gene from his flock most efficiently? 

 

7. In man, normal pigmentation is due to a dominant gene (C), albinism to its recessive allele (c). A normal man marries an albino woman. Their first child is an albino, what are the genotypes of these three persons? man ___________________________ ,

woman ________________________, child ______________________________

8. If they were to have another child, what would be the probability that he or she would have normal pigmentation? _____________________________% (see problem 7)

9. In garden peas, tall plants (T) are dominant over short plants (t) and colored flowers (W) are dominant over white flowers (w). What are the genotypes, phenotypes, and phenotypes ratio in the F1 and F2 from a cross of TTWW x ttww?

 

10. In the F2 dihybrid population of the cross mentioned in question #9:

  • a. What proportion of the tall plants are pure (homozygous) for tallness? ________

  • b. What proportion of the white-flowered plants are pure for white flowers? ______

  • c. What proportion of the tall, white-flowered plants are pure for both tallness and white flowers? _____________

  • d. What proportion of tall, colored flowered plants are pure for both tallness and colored flowers? ____________

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    11. A child with type O blood born to a type A mother could not have a natural father whose blood type is what type? 

    12. During the lifetime of a woman having the genotype MmTT what proportion of the ova she produces will contain a) M and T __________, b) m and T ______________ , c) m and t ______________

    13. A man with the genotype Mm produces two kinds of sperm relative to these genes. A man with the genotype MmTt produces 4 kinds of sperm. How many kinds of sperm are produced by a man with the genotype MmTtWw? List the different kinds.

     

    14. In summer squash, white fruit color is governed by a dominant allele (W) and yellow fruit color by the recessive (w). A dominant allele at another locus (S) produces disc shaped fruit and its recessive allele (s) yields sphere-shaped fruit. If a homozygous white disc variety of genotype WWSS is crossed with a homozygous yellow sphere variety (wwss), the F1 are all white disc dihybrids of genotype WwSs. If the F1 is allowed to mate at random, what would be the phenotypic ratio expected in the F2 generation?

     

    15. Short hair in rabbits is governed by a dominant gene (L) and long hair by its recessive allele (l). Black hair results from the action of the dominant genotype (B) and brown from the recessive genotype (bb). (a) In crosses between dihybrid (heterozygous) short, black and homozygous short, brown rabbits, what genoytpic and phenotypic ratios are expected among their progeny? (b) Determine the expected genotypic and phenotypic ratios in progeny from the cross LlBb x Llbb.

     

     

    16. A sex-linked recessive gene (c) produces red-green blindness in man. A normal woman whose father was color blind marries a color blind man. (a) What genotypes are possible for the mother of the color blind man? (b) What are the chances that the first child from this marriage will be a color blind boy? (c) Of all the girls produced by these parents, what percentage is expected to be color blind? (d) Of all the children (sex unspecified) from these parents, what proportion is expected to be normal?

     

     

    17. The gene for yellow body color (w) in Drosophila is recessive and sex-linked. Its dominant allele (W) produces wild type color. What phenotypic ratios are expected from the crosses (a) yellow male x yellow female, (b) yellow female x wild type male, (c) wild type female (homozygous) x yellow male, (d) wild type (carrier) female x wild type male, (e) wild type (carrier) female x yellow male?

     

     

    18.Male house cats may be black or orange. Females may be black, calico pattern, or orange. (a) If these colors are governed by a sex-linked locus how can these results be explained? (b) Using appropriate symbols, determine the phenotypes expected in the offspring from the cross orange female x black male. (c) Do the same for the reciprocal cross of part (b). (d) A certain kind of mating produces females, half of which are calico and half are black; half the males are orange and half are black: What colors are the parental males and females in such crosses? (e) Another kind of mating produces offspring, 3 of which are orange males, 3 orange females, 3 black males and 3 calico females. What colors are the parental males and females in such crosses? Suggested NOTE: White patches commonly present on calico cats. These are caused by an autosomal allele called piebald.