SAT Subject Biology Practice Question 230: Answer and Explanation

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Question: 230

20. In fruit flies, normal-sized, solid-colored body and red eyes are wild- type (normal) traits. Flies can be assumed to have these traits unless otherwise stated. A geneticist crosses fruit flies from a strain with purple eyes and with fruit flies from a strain with dwarf bodies. The results of the F1 cross are shown below. The scientist then crosses F1 flies together. Results from the F2 generation are included in the table.

GENERATIONNORMAL SIZE, PURPLE EYENORMAL SIZE, RED EYEDWARF, PURPLE EYEDWARF, RED EYETOTAL
F1074200742
F21023183395548/

The allele resulting in purple eyes is located near an allele resulting in streaks across the body, on the same chromosome. The streaked body phenotype is recessive. Crosses are performed with

A.
B.
C.
D.
E.

Correct Answer: E

Explanation:

The streaked parent will be homozygous for the recessive streaked allele. It will have a str allele next to a wild-type allele for eye color, pur+. A purple-eyed parent will be homozygous for the recessive purple-eye allele. It will have a pur allele next to a wild-type allele for body color, str+. Each F2 fly will have one of each type of chromosome.

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