Problem 4


A black guinea pig crossed with an albino guinea pig produced 12 black offspring. When the albino was crossed with a second one, 7 blacks and 5 albinos were obtained.

What is the best explanation for this genetic situation?

Black is dominant over white

 

Write genotypes for the parents, gametes, and offspring.

First cross:

Parent's genotypes

=

BB (black)
x
bb (white)

gametes

=

B

b

F1 offspring

=

all Bb

Second cross:

Parent's genotypes

=

Bb (black)
x
bb (white)

gametes

=

B or b

b

F1 offspring

=

Bb or bb

There should be 50% black to 50% white offspring in this cross.