45 Genetics Problems PDF

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45 Genetics problems 1. Assume that white color is dominant over yellow color in squash. If pollen from the anthers of a heterozygous white-fruited plant is placed on the pistil of a yellow-fruited plant, show, using ratios, the genotypes and phenotypes you would expect the seeds from this cross to produce. 2. In human beings, brown eyes are usually dominant over blue eyes. Suppose a blueeyed man has several children with a brown-eyed woman whose father was blue-eyed. What proportion of their children would you predict will have blue eyes? 3. If a brown-eyed man has ten children with a blue-eyed woman, all brown-eyed, can you be certain that the man is homozygous? If the eleventh child has brown eyes, will that prove what the father's genotype is? 4. A brown-eyed man whose father was brown-eyed and whose mother was blue-eyed has a blue-eyed son with a blue-eyed woman whose father and mother were both browneyed. For which of the individuals mentioned can you be sure of the genotypes? What are their genotypes? What genotypes are possible for the others? 5. If the litter resulting from the mating of two short-tailed cats contains three kittens without tails, two with long tails, and six with short tails, what would be the simplest way of explaining the inheritance of tail length in these cats? Show genotypes. 6. In the fruit fly Drosophila melanogaster, vestigial wings and hairy body are produced by two recessive genes located on different chromosomes. The normal alleles, long wings and hairless body, are dominant. Suppose a vestigial-winged hairy male is crossed with a homozygous normal female. What types of progeny would be expected? If the F1 (first gneration) from this cross are permitted to mate randomly among themselves, what progeny would be expected in the F2 (second generation)? Show complete genotypes, phenotypes, and ratios for each generation. 7. Suppose a hairy female heterozygous for vestigial wing is crossed with a vestigialwinged male heterozygous for the hairy character. What will be the characteristics of the F1? 8. In some breeds of dogs, a dominant gene controls the characteristic of barking while trailing. In these dogs, another independent gene produces erect ears; it is dominant over its allele for drooping ears. Suppose a dog breeder wants to produce a pure-breeding strain of droop-eared barkers, but he knows that the genes for silent trailing and erect ears are present in his kennels. How should he proceed? 9. In hogs, a gene that produces a white belt around the animal's body is dominant over its allele for a uniformly colored body. Another gene produces a fusion of the two hoofs on each foot, a condition known as syndactyly; this gene is dominant over its allele, which produces normal hoofs. Suppose a uniformly colored hog homozygous for

syndactyly is mated with a normal-footed hog homozygous for the belted character. What would be the phenotype of the F1? If the F1 were allowed to breed freely among themselves, what genotype and phenotype ratios would you predict for the F2? 10. In watermelons, the genes for green color and for short shape are dominant over their alleles for striped color and for long shape. Suppose a plant with long striped fruit is crossed with a plant that is heterozygous for both of these characters. What phenotypes would this cross produce and in what ratios? 11. In peas, a gene for tall plants (T) is dominant over its allele for short plants (t). The gene for smooth peas (S) is dominant over its allele for wrinkled peas (s). Calculate phenotypic and genotypic ratios for the results of each of the following crosses: TtSs x TtSs, Ttss x ttss, ttSs x Ttss, TTss x ttSS. 12. A dominant gene, A, causes yellow color in rats. The dominant allele of another independent gene, R, produces black coat color. When the two dominants occur together (A_R_), they interact to produce gray. Rats of the genotype aarr are cream-colored. If a gray male and yellow female produce approximately 3/8 yellow, 3/8 gray, 1/8 cream, and 1/8 black offspring, what are the genotypes of the two parents? 13. What are the genotypes of a yellow male and black female rat that produce 46 gray and 53 yellow offspring? 14. In Leghorn chickens, colored feathers are due to a dominant gene, C; white feathers are due to its recessive allele, c. Another dominant gene, I, inhibits expression of color in birds with genotypes CC or Cc. Consequently both C_I_ and cc__ are white. A colored cock is mated with a white hen and produces many offspring, all colored. Give the genotypes of both parents and offspring. 15. If the dominant gene K is necessary for hearing, and the dominant gene M results in deafness no matter what other genes are present, what percentage of the offspring produced by the cross kkMm x Kkmm will be deaf? (Assume that there is no linkage). 16. What fraction of the offspring of parents each with the genotype KkLlMm will be kkllmm? 17. Suppose two DdEeFfGgHh individuals are mated. What would be the predicted frequency of ddEEFfggHh offspring from such a mating? 18. If a man with blood type B, one of whose parents had blood type O, has children with a woman with blood type AB, what will be the theoretical percentage of their children with blood type B? 19. Both Ms. Smith and Ms. Jones had babies the same day in the same hospital. Ms. Smith took home a baby girl, whom she names Shirley. Ms. Jones took home a baby girl, whom she named Jane. Ms. Jones began to suspect, however, that her child had been

accidentally switched with the Smith baby in the nursery. Blood tests were made; the father of Ms. Smith's baby was type A, Ms. Smith was type B, the father of Ms. Jones' baby was type A, Ms. Jones was type A, Shirley was type O, and Jane was type B. Had a mixup occurred? 20. When Mexican Hairless dogs are crossed with normally-haired dogs, about half the pups are hairless and half have hair. When, however, two Mexican Hairless dogs are mated, some deformed puppies are born dead. Explain the results. 21. Suppose a pigeon breeder finds that about one fourth of the eggs produced by one of his prize pairs do not hatch. Of the young birds produced by this pair, two thirds are males. Give a possible explanation for these results. (Remember the mechanism of sex determination in birds.) 22. Red-green color blindness is inherited as a sex-linked recessive. If a color-blind woman marries a man who has normal vision, what would be the expected phenotypes of their children with reference to this character? 23. Suppose that gene b is sex-linked, recessive, and lethal. A man has children with a woman who is heterozygous for this gene. If this couple had many normal children, what would be the predicted sex ratio of these children? 24. A man and his partner both have normal color vision, but a daughter has red-green color blindness, a sex-linked recessive trait. The man sues his partner on the grounds of infidelity. Can genetics provide evidence supporting his case? 25. It is exceedingly difficult to determine the sex of very young chickens, but it is easy to tell, by visual observation, whether or not they are barred. The barred pattern is inherited as a sex-linked dominant. Set up a cross so that the sex of all chicks can be determined when they hatch. (Remember that chickens are birds- ZZ = male, ZW = female) 26. a. In cats, short hair is dominant over long hair; the gene involved is autosomal. Another gene, B1, which is sex-linked, produces yellow coat; its allele B2 produces black coat color; and the heterozygous combination B1B2 produces tortoise-shell coat color. If a long-haired black male is mated with a tortoise-shell female homozygous for short hair, what kind of kittens will be produced in the F1? b. If the F1 cats are allowed to interbreed freely among themselves, what are the chances of obtaining a long-haired yellow male? 27. In silkworms, yellow (Y) cocoons are dominant over white (y). If a silkworm mother from a pure yellow cocoon is crossed with a male from a pure white one, what will be the appearance of the cocoons in the offspring? b. What results when these hybrids are crossed?

c. What results when the yellow-cocoon hybrid moths are crossed back to the pure yellow-cocoon parents? d. What results when the yellow-cocoon hybrid moths are crossed back to the white parent? e. What kind of gametes will be produced by (a) pure yellow-cocoon parents, (b) hybrid yellow-cocoon parents, or (c) white-cocoon parents? f. What genotype and phenotype ratios are to be expected from the following crosses: (1) P1: Yellow x White (2) P1: Yellow x White (3) P1: Yellow x Yellow (4) P1: Yellow x Yellow g. If two yellow-cocoon parents produce about 3/4 yellow-cocoon offspring, what are the genotypes of the parents? h. How would you determine whether yellow-cocoon moths are pure (homozygous) or hybrid (heterozygous) if yoiu have the live moths? (Assume you have access to whitecocoon moths also.) i. How would you determine whether white-cocoon moths are pure or hybrid? 28. In humans, curly hair (S) is dominant over straight hair (s); brown eyes (B) over blue eyes (b); and right handedness (R) over left-handedness (r). Color blindness (c) is recessive and sex-linked. A curly-haired, brown-eyed, left-handed man has children with a curly-haired, blue-eyed, right-handed woman. Both have normal color vision. They have five children, as follows: a- a daughter, curly-haired, blue-eyed, right-handed, normal vision b- a daughter, straight-haired, blue-eyed, right-handed, normal vision c- a son, curly-haired, brown-eyed, right-handed, color blind d- a son, curly-haired, browneyed, right-handed, normal vision e- a son, curly-haired, blue-eyed, right-handed, normal vision What is the genotype of each parent? 29. Vermillion eye in Drosophila is a recessive sex-linked character. What will be the nature of the offspring of a vermillion female and a wild type (red) male? 30. White eye in Drosophila is a recessive sex-linked character. Vestigial wing is a recessive autosomal character. What will be the appearance of the F1 and F2 generations from a cross between a white-eyed homozygous long-winged female and a red-eyed vesigial male? 31. In cats, yellow is due to a factor (Y), and black to its allele (y). The heterozygous condition Yy results in tortoise shell. The factors Y and y are sex-linked. What kinds of offspring would be expected to result from the cross of a black male with a yellow female?

32. What kinds of offspring would be expected to result from the cross of a black male with a tortoise shell female? 33. A yellow male is mated with a tortoise shell female. If the female has a litter consisting of four male kittens, what colors would they most probably be? 34. In humans, aniridia (a type of blindness) is due to a dominant factor. Optic atrophy (another type of blindness) is due to a recessive sex-linked factor. A man blind from optic atrophy has a female partner who is blind from aniridia. Would any of their children be expected to be blind? Which type of blindness would they have? 35. In humans, assume that brown eyes (B) are dominant over blue eyes (b) and that right-handedness (R) dominates left-handedness (r). What offspring may be expected from the pairing of a right-handed, blue-eyed man whose father was left-handed, with a brown-eyed woman from a family in which all of the members have been brown-eyed and right-handed for several generations? 36. A brown-eyed, right-handed man has children with a brown-eyed, right-handed woman. Their first child is blue-eyed and left-handed. If other children are born to this couple, what probably will be their appearance with respect to these two traits? 37. Parent A is feeble-minded (n) and deaf (d); only one of his parents was deaf. Parent B is normal-minded (N) and deaf (d); only one her parents was deaf, but one was feebleminded. What is the genotype of parents A and B? What are the genotypes of their possible offspring? 38. What is the ratio of probability that the first child will be (1) normal-minded, deaf, (2) normal-minded, normal hearing, (3) feeble-minded, deaf, (4) feebel-minded, normal hearing? 39. If six children from these parents fall into groups 1 & 3, what is the expectation from the seventh child? 40. In cocker spaniels, black is due to a dominant factor B, red to its recessive allele b. Solid color is dependent upon a dominant factor S, white spotting upon its recessive allele s. A red male was mated to a black-and-while female. They had five puppies, as follows: 1 black, 1 red, 1 black/white, 2 red/white. What were the parents' genotypes? 41. A black male was mated to a black female. They had six puppies, all black. What were the probable genotypes of the parents? Why can the genotypes in this case not be given with the same accuracy as those in 9a? 42. In poultry, white may be due to homozygous condition of either or both of the recessive factors c and o. Color depends upon the presence of both dominants C and O. White males of genotype CCoo were crossed with white females of genotype ccOO. The colored F1 birds were crossed to double-recessives ccoo. From many such crosses the

total results were as follows: 68 colored, 204 white. Are these factors linked? If so, what is the percent of crossing over? 43. A black-bodied, purple-eyed Drosophila, mated with a homozygous gray, red-eyed fly, produced all gray, red-eyed offspring. One of the female offspring mated with a black, purple-eyed male and produced 104 gray, red, 94 black-purple, 6 gray, purple, and 7 black, red offspring. What is the percentage of crossing over between body color and eye color? 44. A colorblind woman pairs with a man with normal vision. What kind of children would be expected from such a union? Color blindness is recessive and sex-linked. 45. A woman with normal vision pairs with a man with normal vision and they have a colorblind son. The first partner dies and she pairs with a colorblind man. Show the types of children that might be expected from this second pairing and the proportion of each....