SAT Subject Biology Practice Question 227: Answer and Explanation
17. 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.
|GENERATION||NORMAL SIZE, PURPLE EYE||NORMAL SIZE, RED EYE||DWARF, PURPLE EYE||DWARF, RED EYE||TOTAL|
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. I and III
B. I and IV
C. II and III
D. II and IV
E. III only
Correct Answer: C
The parent cross resulted in an F1 generation with normal-sized bodies and red eyes only. This indicates that these traits are dominant and that a dwarf body and purple eyes are recessive traits.