Question

In a cross between a black and white guinea pig, all members of the F1 generation are black. The F2 generation is 3/4 black and 1/4 white. a) Diagram the cross, showing phenotypes and genotypes b) What will be the offspring if two F2 white guinea pigs are crossed? c) Two different mattings were made between black members of the F2 generation, with the following results: →Cross 1 All Black →Cross 2 3/4 black, 1/4 white

Answer 1

When two guinea pigs, one black (BB) and one white (bb), are crossed, all F1 offspring are black (Bb). For the F2 generation, the phenotypic ratio is 3 black to 1 white. When two F2 white guinea pigs (bb) are crossed, all offspring are white (bb).

Step-by-step explanation:

Cross Between Black and White Guinea Pigs

Assuming black color (B) is dominant over white color (b), and parent guinea pigs are homozygous for their color (BB for black and bb for white), the F1 generation will all be heterozygous (Bb) and black.

a) Diagram of the Cross

Parental Generation (P): BB (black) x bb (white)

F1 Generation: All offspring are Bb (black)

F2 Generation (Bb x Bb):

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• 
  
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The

phenotypic ratio

for the F2 generation is

3 black:1 white

.

b) Offspring of F2 White Guinea Pigs

If two F2 guinea pigs that are white (bb) are crossed, all offspring will be white (bb).

c) F2 Generation Black Offspring Crosses

Cross 1: All Black (this indicates the parents were likely BB x BB or BB x Bb)

Cross 2: 3/4 black, 1/4 white (this indicates the parents were likely Bb x Bb)