PRACTICE GENETICS PROBLEMS TO BE COMPLETED

1. In tomatoes R = red fruit dominant to r = yellow fruit. If a tomato plant homozygous for red fruit is crossed with one with yellow fruit, what will be the genotypes and phenotypes in the F1 generation? Cross two members of the F1 and list the genotypes, phenotypes and ration expected in the F2. Which of the F2are homozygous? Heterozygous?

2. In a man, the gene for non-blue eyes (brown, hazel, gray, etc.) is dominant over the gene for blue eyes. If two non-blue eyed parents have four children, two non-blue eyed and two blue eyed, what are the genotypes of the parents? How could you explain this ratio?

3. Mr. and Mrs. Jones had just had a child and went to visit Mr. and Mrs. Smith who also just had a child. Each couple wanted to show their child to the other couple. Mr. Jones had blue eyes as did his wife. Mr. Smith had brown eyes and his wife had blue eyes. Baby A had blue eyes and baby B had brown eyes. Which baby belonged to which couple?

4. Brachydactyly is a rate human trait that causes a shortening of the fingers. Various

investigations have shown that approximately half the progeny of brachydactyly x

normal marriages are brachydactylous. What proportion of brachydactylous offspring

would be expected in matings between two brachydactylous individuals?

5. In Cocker Spaniels, solid coat color is dominant over spotted coat. Suppose a true-breeding, solid-colored dog is crossed with a spotted dog, and F1 dogs are interbred. What is the probability that the first puppy will have a spotted coat? What is the probability that, if four puppies are born, all of them will have a solid coat?

6. Sickle cell disease is caused by a genetic defect in the coding for the amino acid sequence of hemoglobin, causing abnormal red blood cells. Heterozygous persons appear normal, but when the blood is held under low oxygen concentration, their red blood cells also become sickle-shaped. A young woman has a brother who died of sickle cell disease, and she is concerned about the chance of the condition appearing in her children. When blood samples are taken and placed under low-oxygen concentration, her red blood cells become sickled, but those of her prospective husband remain normal. What is the probability of their children having this disease?

7. In flowers with incomplete dominance use R = red flowers and r = whiteflowers. A heterozygous pink flower is crossed with a white flower. In such a cross what % would be red? What % pink? What % white?

8. We have spoken of alleles as being dominant or recessive as if there were no other possibilities. But somehow one allele of a pair is not completely dominant over the other. In shorthorn cattle, for instance, when a red bull (RR) is crossed with a white cow (rr), their heterozygous offspring (Rr) are neither red nor white, but roan (having intermingled red and white hairs). If a roan bull (Rr) is crossed with a roan cow (Rr), the calf has one chance in four of being white (rr), two chances in four of being roan (Rr), and one chance in four of being red (RR).

a) Using symbols work out a cross of roan with red.

b) A farmer wants to establish a pure strain of roan cattle that breeds true. Why

is this impossible?

9. In poppies, R = red flowers, r = white flowers, but R is not dominant to r. Instead

R and r work together when they exist in the same cell and produce a “blend” in that Rr produces pink flowers. If two pink flowers are crossed, what are the genotypes, phenotypes and ratios expected? This is an example of non-dominance or incomplete dominance..

10. A man’s maternal grandfather has type AB blood while all other grandparents are

type O. What are the chances of the man being: A? B? AB? O?

11. John has type O blood, his father type B, and his mother type A. What are the genotypes of John’s parents?

12. Suppose two newborn babies are accidentally mixed up in the hospital and there was a question of which baby belonged to which parents. From the following blood types, determine which baby belongs to which parents:

Baby 1Type O

Baby 2Type A

Mrs. BrownType B

Mr. BrownTypeAB

Mrs. SmithType B

Mr. SmithType B

Now determine the genotype of each of the six people in the problem.

13. In guinea pigs, black coat is dominant to white coat and short hair is dominant to long hair. A man was given a black short-haired guinea pig. In an effort to find out the animal’s genotype, the man performed a test cross with a white long-haired animal several times. The results of the crosses were as follows: 18 black short-haired and 21 black long-haired. Using B for black, b for white, S for short and s for long hair, what is the genotype of the man’s black guinea pig? Of the test cross animal? Of the offspring?

14. Congenital deafness in man is due to the homozygous condition of either or both of the recessive factors d and e. Both dominant factors D and E are necessary for normal hearing. A deaf man married a deaf woman and all seven children have normal hearing. What are the genotypes of the parents and children?

15. In moose, H = antlered dominant to h = not antlered. If B = bearded dominant to b = non-bearded in the same animal, what parents would a non-antlered, non-bearded moose have (genotypically) is both parents were antlered and bearded?

16. A man’s maternal grandmother has normal vision; his maternal grandfather was colorblind; his mother is colorblind; his father has normal vision. What are the genotypes as to vision of the parents and grandparents mentioned? What type of vision has the man himself? What type do his sisters have? If he should marry a woman genotypically like one of his sisters, what type of vision would be expected in the offspring?

17. The bleeders disease, hemophilia, is sex linked. A man and his wife have 2 boys and

4 girls. One of the boys has hemophilia. The other boy and the girls do not. What are

thegenotypes of the parents?

18. Why is it not possible for a male to heterozygous for colorblindness?

19. Color black and yellow in cats is sex linked. Possession of allele b produces black, y

produces yellow.The combination (by) produces tortoise shell or tricolor (black, yellow, and white markings)

a) Cross a black male with a tortoise shell female and describe the phenotypes and ratios expected.

b) Cross a black male with a yellow female and give genotypes, phenotypes and ratios expected.

20. As Mendel discovered, gray seed color in peas is dominant to white. In the following

experiments, parents with known phenotypes but unknown genotypes produced the listed

progeny:

Progeny

ParentsGrayWhite

(a) gray x white 82 78

(b) gray x gray 118 39

(c) white x white 0 50

(d) gray x white 74 0

(e) gray x gray 90 0

Using the letter G for the gray gene and g for white, give the most probable genotype of each parent.

21. In crosses (b), (d), and (e) of Problem 20, indicate how many of the gray progeny produced by each cross would be expected to produce white progeny when self-fertilized.

22. The following is a pedigree of a fairly common human hereditary trait (shaded symbols):

I.

II.

III.

a)Indicate whether you think the gene differences causing this effect are

dominant or recessive, e.g., A (dominant) or a (recessive).

b)Designate the genotype of each individual in the pedigree, and indicate the choice of genotypes if you think more than one genotype if possible for an individual.

23. In four-o’clock plants, the allele for red flower color has an effect that is incompletely dominant over the effect of the white color allele. If a cross between two plants produced 18 red, 32 pink, and 15 white plants, what are the phenotypes of the parents?

24. In cattle, the effect of the allele producing red coat color (R) in incompletely dominant over the effect of the allele producing white coat color (r), the heterozygote being roan-colored (Rr). On the other hand, the effects of alleles for the absence of horns show complete dominance; HH and Hh are hornless or “polled”, and hh ir horned. On the assumption that these two gene pairs assort independently:

  1. What would be the phenotype of the F1 derived from a mating RRHH x rrhh?
  2. What would be the phenotypes and their proportions in an F2 derived from crossing F1 x F1?
  3. What would be the phenotypic proportions among the progeny derived from crossing F1 individuals to the original white horned stock?

25.Petrakis, Molohon, and Tepper investigated the inheritance of different types of earwax (cerumen) among American Indians living in the United States and observed that an individual could have one of the two types of earwax, dry or sticky, which were inherited in the fashion shown by the following data:

Offspring

ParentalNumber of

Combination MatingsStickyDry

sticky x sticky 10326

sticky x dry 8209

dry x dry 12 0 42

On the basis of these data explain whether the inheritance of dry earwax is caused

by dominance, recessiveness, partial dominance, co-dominance, or some other mode.

26.Some investigators found that matings between horses with pale cream coat color to horses with chestnut coat color produced exclusively “palomino” individuals with intermediate coat color. A number of matings between palominos themselves produced 19 pale cream, 21 chestnut, and 44 palominos.

a) Define gene symbols and suggest genotypes for the three coat colors.

b) If a palomino horse breeder wanted to eliminate pale cream individuals both as parents and as offspring, but nevertheless wanted to obtain as many palominos as possible, what breeding method would you suggest that he follow?

27.What phenotypes and ratios would you expect among the offspring of the following crosses:

a. IA IA x ii ?b. IA IA x IAIB ?c. IA IA x IBi ?

d. IA IA x IAi ?e. IAi x IAi ?f. IAi x IB IA ?

g. IAi x ii ?

  1. A common kind of red-green color blindness in humans is caused by the presence of a sex-linked recessive gene c, whose normal allele is XC. Using these genes, what are all the possible colorblind genotypes and their corresponding phenotypes in males and in females?
  1. (a) Can two colorblind parents produce a normal son?(b) A normal daughter?

(c) Can two normal parents produce a colorblind son? (d) A colorblind daughter?

(d) Can a normal daughter have a colorblind father?(e) A colorblind mother?

(f) Can a colorblind daughter have a normal father? (g) A normal mother?

30. A colorblind woman marries a normal-visioned man. They have two children, a boy and a girl:

  1. what will be the genotype and phenotype of the boy?
  2. what will be the genotype and phenotype of the girl?

31. A woman of A blood type and normal color vision produced five children as follows:

  1. male, A blood type, colorblind;
  2. male, O blood type, colorblind;
  3. female, A blood type, colorblind;
  4. female, B blood type, normal color vision;
  5. female, A blood type, normal color vision.

Of the two husbands that may have mated with this woman at different times, no. 1 had AB blood type and was colorblind, and no. 2 had A blood type with normal color vision. Which of these men is the most probable father in each case?

  1. Mary has blue eyes (a recessive phenotype), but both her mother and father have brown eyes. What are the chances that a child in this family will have blue eyes?brown eyes?
  1. Red flowers are dominant to white flowers in peas. Inflated pods are dominant to constricted pods. If a pea, which is heterozygous for red flowers and for inflated pods, is crossed with a pea with white flowers and constricted pods, what will the ratio of red-inflated to red-constricted to white-inflated to white-constricted be?

34.The only member of Judy’s family who is color blind is her brother Jim. What is Jim’s genotype? The father’s genotype? The mother’s genotype? What is Judy’s genotype is she later has a color blind son?

35.A child wonders if she is adopted and hence compares her blood type to those of her “parents.” Her father is type AB and her mother is type O. What blood type of the child would indicate that she might have been adopted?

  1. A couple unable to conceive in any other way chooses to have a fertilization accomplished in a test tube, followed by uterine implantation. The procedure is successful, but after birth, the woman claims the child is not hers and the doctor mixed up the ova. In the resulting maternity suit, the following data came to light. The woman’s father was color blind, her blood type is B, and she suffers from sickle cell disease. The man has blood type A, is not color blind, and is a sickle cell carrier. The child, a male, has blood type AB, is color blind, and does not carry the sickle cell trait, either heterozygously or homozygously. Which of the following is (are) true?

a. The data from the blood typing prove the woman is the mother.

b. The color blindness data prove the woman is the mother.

c. The sickle cell trait data prove the woman is the mother.

d. The data indicates that the woman is not the mother.

e. The data are insufficient to determine the maternity of the mother.

  1. About 70% of Americans get a bitter taste from the drug phenyl thiocarbamide (PTC); the others do not. The ability to taste this drug results from a dominant gene, while taste blindness is recessive. A normally pigmented woman who is taste blind and has an albino father who is a taster. She marries an albino man who is a taster, but who has a mother who is taste blind. What type of children might this couple have?

38. In garden peas, tall stem is dominant over short stem, green pods are dominant over yellow pods, and smooth seeds are dominant over wrinkled seeds. Suppose a homozygous short, green, wrinkled pea plant is crossed with a homozygous tall, yellow, smooth one. What will be the appearance of the F1 generation? What proportion of the F2 generation will have the tall, yellow, and wrinkled traits?

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