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GT/Honors Advanced Biology

Quiz Item Bank: Codominant/Multiple Alleles/Dihybrid Crosses/Pedigrees/Recombination


  1. A classical example of multiple alleles is found in the ABO blood group system of humans, where the allele IA for the A antigen is codominant with the allele IB for the B antigen.  Both IA and IB are completely dominant to the allele i, which fails to specify any detectable antigenic structure.  The hierarchy of dominance relationships is symbolized as (IA = IB) > i.


A man is suing his wife for divorce on the grounds of infidelity.  Their first child and second child, whom they both claim, are blood groups O and AB, respectively.  The third child, whom the man disclaims, is blood type A.  Is it possible that the man is the father of the third child?  EXPLAIN!!!


  1. Thalassemia is a hereditary disease of the blood of humans resulting in anemia.  Severe anemia (thalassemia major) is found homozygous (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 by normals would expected to be normal, (b) what fraction of the adult F1 from marriages of minors by minors would be expected to be anemic?


  1. 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 the Dutch belt; the sh allele produces Hereford-type spotting; solid color is a result of the sc 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.


  1. In fruit flies, we can consider two traits, cinnabar eye color (recessive) and black body color (recessive).  Wild-type eye color (cn+) will result in the reddish eye color, whereas wild-type body color (b+) will result in a brownish body color.  If we cross a heterozygous fruit fly (for both traits) by a completely homozygous recessive fruit fly, what would be the expected phenotypic ratios in the F1?


  1. The gene for spotted coat color in rabbits (s+) is dominant to its allele for solid color (s).  In the following pedigree assume that those individuals brought into the family from outside do not carry the gene for solid color, unless there is evidence to the contrary.


    1. Write the genotype for each individual insofar as you can definitively ascertain.
    2. What s the probability of progeny having the solid phenotype from a mating between III-2 and III-6.



  1. A multiple allelic series is know to govern the intensity of pigmentation in the mouse such that D = full color, d = dilute color, and dl is lethal when homozygous.  The dominance order is D > d > dl.  A full-colored mouse carrying the lethal is mated to a dilute-colored mouse also carrying the lethal.  The F1 is backcrossed to the dilute parent.  (a) What phenotypic ratio is expected in the viable backcross progeny?  (b) What percentage of full-colored backcross progeny carry the lethal?  (c) What fraction of the dilute-colored progeny carry the lethal?


  1. The shape of radishes may be long (SLSL), round (SRSR), or oval (SLSR).  If long radishes are crossed to oval radishes and the F1 the allowed to cross at random among themselves, what phenotypic ratio is expected in the F2?


  1. The Palomino horse is a hybrid exhibiting a golden color with lighter mane and tail.  A pair 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:Non-Palomino ratio among the offspring.  (b) What percentage of the non-Palomino offspring in part (a) will breed true? (c) What kind of breeding will produce only Palomino?


  1. A pair of codominant alleles is known to govern cotyledon leaf color in soybeans.  The homozygous genotype CGCG produces dark green, the heterozygous genotype CGCY produces light green, 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?


  1. 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 X Ee, (b) EDe X EE?