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Patterns of Inheritance Practice Test (page 2)

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By — McGraw-Hill Professional
Updated on Aug 19, 2011

Dominant and Recessive Alleles Questions

  1. Several black guinea pigs of the same genotype were mated and they produced 29 black and 9 white offspring. What would you predict the genotypes of the parents to be?
  2. If a black female guinea pig is testcrossed and produces at least one white offspring, determine (a) the genotype and phenotype of the sire (male parent) that produced the white offspring, (b) the genotype of this female.
  3. In Drosophila, sepia-colored eyes are due to a recessive allele s and wild type (red eye color) to its dominant allele s+. If sepia-eyed females are crossed to pure wild-type males, what phenotypic and genotypic ratios are expected if the F2 males are backcrossed to the sepia-eyed parental females?
  4. The lack of pigmentation, called albinism, in humans is the result of a recessive allele a and normal pigmentation is the result of its dominant allele A. Two normal parents have an albino child. Determine the probability that (a) the next child is albino, (b) the next two children are albinos. (c) What is the chance of these parents producing two children, one albino and the other normal?
  5. Short hair is due to a dominant gene L in rabbits, and long hair to its recessive allele l. A cross between a short-haired female and a long-haired male produces a litter of one long-haired and seven short-haired bunnies. (a) What are the genotypes of the parents? (b) What phenotypic ratio was expected in the offspring generation? (c) How many of the eight bunnies were expected to be long-haired?
  6. Black wool of sheep is due to a recessive allele b and white wool to its dominant allele B. A white ram (male) is crossed to a white ewe (female), both animals carrying the allele for black. They produce a white male lamb that is then backcrossed to the female parent. What is the probability of the backcross offspring being black?
  7. In foxes, silver-black coat color is governed by a recessive allele b and red color by its dominant allele B. Determine the genotypic and phenotypic ratios expected from the following matings: (a) pure red ×carrier red, (b) carrier red × silver-black, (c) pure red × silver-black.

Codominance and Incomplete Dominance Questions

  1. When chickens with splashed white feathers are crossed with black-feathered birds, their offspring are all slate blue (Blue Andalusian). When Blue Andalusians are crossed among themselves, they produce splashed white, blue, and black offspring in the ratio of 1 : 2 : 1, respectively. (a)Howare these feather traits inherited? (b) Using any appropriate symbols, indicate the genotypes for each phenotype.
  2. The shape of radishes may be long (SLSL), round (SRSR), or oval (SLSR). If long radishes are crossed to oval radishes and the F1 then allowed to cross at random among themselves, what phenotypic ratio is expected in the F2?
  3. Apalomino horse is a hybrid exhibiting a golden color with lighter mane and tail.Apair of codominant alleles (D1 and D2) is known to be involved in the inheritance of these coat colors. Genotypes homozygous for the D1 allele are chestnut-colored (reddish), heterozygous genotypes are palomino-colored, and genotypes homozygous for the D2 allele are almost white and called cremello. (a) From matings between palominos, determine the expected palomino : nonpalomino ratio among the offspring. (b) What percentage of the nonpalomino offspring in part (a) will breed true? (c) What kind of mating will produce only palominos?

Lethal Alleles Questions

  1. Chickens with shortened wings and legs are called "creepers." When creepers are mated to normal birds they produce creepers and normals with equal frequency. When creepers are mated to creepers they produce two creepers to one normal. Crosses between normal birds produce only normal progeny. How can these results be explained?
  2. In the Mexican Hairless breed of dogs, the hairless condition is produced by the heterozygous genotype (Hh). Normal dogs are homozygous recessive (hh). Puppies homozygous for the H allele are usually born dead, with abnormalities of the mouth and absence of external ears. If the average litter size at weaning is six in matings between hairless dogs, what would be the average expected number of hairless and normal offspring at weaning from matings between hairless and normal dogs?
  3. A pair of codominant alleles regulate cotyledon leaf color in soybeans. The homozygous genotype CGCG produces dark-green leaves, the heterozygous genotype CGCY produces light-green leaves, and the other homozygous genotype CYCY produces yellow leaves so deficient in chloroplasts that seedlings do not grow to maturity. If dark-green plants are pollinated only by light-green plants and the F1 crosses are made at random to produce an F2, what phenotypic and genotypic ratios would be expected in the mature F2 plants?
  4. Thalassemia is a hereditary disease of the blood of humans that results in anemia. Severe anemia (thalassemia major) is found in homozygotes (TMTM) and a milder form of anemia (thalassemia minor) is found in heterozygotes (TMTN). Normal individuals are homozygous TNTN. If all individuals with thalassemia major die before sexual maturity (a) what proportion of the adult F1 from marriages of thalassemia minors to normals would be expected to be normal, (b) what fraction of the adult F1 from marriages of minors to minors would be expected to be anemic?

Multiple Alleles Questions

  1. A multiple allelic series is known in the Chinese primrose where A (A lexandria type = white eye) > an (normal type = yellow eye) > a (Primrose Queen type = large yellow eye). List all of the genotypes possible for each of the phenotypes in this series.
  2. Plumage color in mallard ducks is dependent upon a set of three alleles: MR for restricted mallard pattern, M for mallard, and m for dusky mallard. The dominance hierarchy is MR > M > m. Determine the genotypic and phenotypic ratios expected in the F1 from the following crosses: (a)MRMR × MRM, (b) MRMR × MRm, (c)MRM × MRm, (d) MRm × Mm, (e) Mm × mm.
  3. A number of self-incompatibility alleles are known in clover such that the growth of a pollen tube down the style of a diploid plant is inhibited when the latter contains the same self-incompatibility allele as that in the pollen tube. Given a series of self-incompatibility alleles S1, S2, S3, S4, what genotypic ratios would be expected in embryos and in endosperms of seeds from the following crosses?
  4. The coat colors of many animals exhibit the "agouti" pattern, which is characterized by a yellow band of pigment near the tip of the hair. In rabbits, a multiple allelic series is known where the genotypes EDED and EDe produce only black (nonagouti), but the heterozygous genotype EDE produces black with a trace of agouti. The genotypes EE or Ee produce full color, and the recessive genotype ee produces reddish-yellow. What phenotypic and genotypic ratios would be expected in the F1 and F2 from the cross (a) EDED × Ee, (b) EDe × ee?
  5. The inheritance of coat colors of cattle involves a multiple allelic series with a dominance hierarchy as follows: S > sh > sc > s. The S allele puts a band of white color around the middle of the animal and is referred to as a Dutch belt; the sh allele produces Hereford-type spotting; solid color is a result of the sh allele; and Holstein-type spotting is due to the s allele. Homozygous Dutch-belted males are crossed to Holstein-type spotted females. The F1 females are crossed to a Hereford-type spotted male of genotype shsc. Predict the genotypic and phenotypic frequencies in the progeny.
  6. The genetics of the ABO human blood groups was presented in Example 2.19. A man of blood group B is being sued by a woman of blood group A for paternity. The woman's child is blood group O. (a) Is this man the father of this child? Explain. (b) If this man actually is the father of this child, specify the genotypes of both parents. (c) If it was impossible for this group B man to be the father of a typeOchild, regardless of the mother's genotype, specify his genotype. (d) If a man was blood group AB, could he be the father of a group O child?

Statistical Distributions Questions

  1. Black hair in the guinea pig is dominant to white hair. In families of five offspring where both parents are heterozygous black, with what frequency would we expect to find (a) three whites and two blacks, (b) two whites and three blacks, (c) one white and four blacks, (d) all whites?
  2. Assuming that boys and girls are equally frequent in a population, in families of five children, what is the probability of finding (a) three or more boys, (b) three or more boys or three or more girls?
  3. A dozen strains of corn are available for a cross-pollination experiment. How many different ways can these strains be paired?
  4. Five coat colors in mice are agouti, cinnamon, black, chocolate, and albino. (a) List all of the possible crosses between different phenotypes. (b) Verify the number of different crosses by applying formula (2.1).
  5. In mice litters of size eight, determine (a) the most frequently expected number of males and females, (b) the term of the binomial that part (a) represents, (c) the percentage of all litters of size eight expected to have four males and four females.

Dihybrid Crosses with Dominant and Recessive Alleles Questions

  1. The position of the flower on the stem of the garden pea is governed by a pair of alleles. Flowers growing in the axils (upper angle between petiole and stem) are produced by the action of a dominant allele T, those growing only at the tip of the stem by its recessive allele t. Colored flowers are produced by a dominant gene C, and white flowers by its recessive allele c. A dihybrid plant with colored flowers in the leaf axils is crossed to a pure strain of the same phenotype. What genotypic and phenotypic ratios are expected in the F1 progeny?
  2. In summer squash, white fruit color is governed by a dominant allele W and yellow fruit color by its recessive allele w. A dominant allele S at another locus produces disk-shaped fruit and its recessive allele s yields sphere-shaped fruit. If a homozygous white disk variety of genotype WWSS is crossed with a homozygous yellow sphere variety wwss, the F1 are all white disk dihybrids of genotype WwSs. If the F1 is allowed to mate at random, what would be the phenotypic ratio expected in the F2 generation?
  3. In Drosophila, ebony body color is produced by a recessive gene a and wild-type (gray) body color by its dominant allele a+. Vestigial wings are governed by a recessive gene vg, and normal wing size (wild type) by its dominant allele vg+. If wild-type dihybrid flies are crossed and produce 256 progeny, how many of these progeny flies are expected in each phenotypic class?
  4. 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 shorthaired, black and homozygous short-haired, brown rabbits, what genotypic and phenotypic ratios are expected among their progeny? (b) Determine the expected genotypic and phenotypic ratios in progeny from the cross LlBb × Llbb.
  5. The genetic information for the following eight parts is found in Problem 2.51. (a) What phenotypic ratio is expected among progeny from crosses of LlBb × LlBb? (b) What percentage of the F1 genotypes in part (a) breeds true (i.e., what percentage is of homozygous genotypes)? (c) What percentage of the F1 genotypes is heterozygous for only one pair of genes? (d) What percentage of the F1 genotypes is heterozygous at both loci? (e) What percentage of the F1 genotypes could be used for testcross purposes (i.e., homozygous double-recessive)? (f) What percentage of the F1 progeny could be used for testcross purposes at the B locus (i.e., homozygous recessive bb)? (g) What percentage of all short-haired F1 individuals is expected to be brown? (h) What percentage of all black F1 individuals will breed true for both black and short hair?
  6. The presence of feathers on the legs of chickens is due to a dominant allele F and clean legs to its recessive allele f. Pea-comb shape is produced by another dominant allele P and single comb by its recessive allele p. In crosses between pure feathered-leg, single-combed individuals and pure pea-combed, clean-leg individuals, suppose that only the single-combed, feathered-leg F2 progeny are saved and allowed to mate at random. What genotypic and phenotypic ratios would be expected among the progeny (F3)?
  7. List all the different gametes produced by the following individuals: (a) AA BB Cc (b) aa Bb Cc, (c) Aa Bb cc Dd, (d) AA Bb Cc dd Ee Ff.
  8. The normal cloven-footed condition in swine is produced by the homozygous recessive genotype mm. A mule-footed condition is produced by the dominant genotype M-. White coat color is governed by the dominant allele of another locus B and black by its recessive allele b. A white, mule-footed sow (female) is mated to a black, cloven-footed boar (male) and produces several litters. Among 26 offspring produced by this mating, all were found to be white with mule feet. (a) What is the most probable genotype of the sow? (b) The next litter produced eight white, mule-footed offspring and one white, cloven-footed pig. Now, what is the most probable genotype of the sow?
  9. A white, mule-footed boar (see Problem 2.55) is crossed to a sow of the same phenotype. Among the F1 offspring there were found to be 6 white, cloven-footed : 7 black, mule-footed : 15 white, mule-footed : 3 black, cloven-footed pigs. (a) If all the black, mule-footed F1 offspring from this type of mating were to be testcrossed, what phenotypic ratio would be expected among the testcross progeny? (b) If the sow were to be testcrossed, what phenotypic ratio of progeny would be expected?
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