Question

Suppose a geneticist uses a three-point testcross to map three recessive, linked hummingbird wing-shape mutations called tk, r, and s, where tk is associated with thick wings, r is associated with round wings, and s is associated with sharp wings. He first crosses homozygous sharp birds to homozygous thick, round birds. Next, he testcrosses the F1 progeny to thick, round, sharp birds. He obtained the results shown. Given this data, label the progeny phenotypic classes as either parental, single crossover (SCO), or double crossover (DCO) recombinant types. Each label may be used multiple times. Two classes have already been filled in. Phenotype Number Recombinant type sharp 781 Answer Bank thick, round 789 SCO DCO round parental thick, sharp 191 SCO thick round, sharp thick, round, sharp SCO wild type

Answer 1

Suppose a geneticist uses a three-point testcross to map three recessive, linked hummingbird wing-shape mutations called tk, r, and s, where tk is associated with thick wings, r is associated with round wings, and s is associated with sharp wings. He first crosses homozygous sharp birds to homozygous thick, round birds. Next, he testcrosses the Fı progeny to thick, round, sharp birds. He obtained the results shown. Given this data, label the progeny phenotypic classes as either parental, single crossover (SCO), or double crossover (DCO) recombinant types. Each label may be used multiple times. Two classes have already been filled in. Phenotype Number Recombinant type sharp 781 Answer Bank thick, round 789 parental parental SCO SCO DCO round 181 parental thick, sharp 191 SCO thick dco dco round, sharp thick, round, sharp SCO SCO wild type

Number of parental progenies is the maximum and DCO is the minimum.

Number of SCO progenies are intermediates.

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