A third grader decided to breed guinea pigs for her school science project. She

Question

A third grader decided to breed guinea pigs for her school science project. She went to the pet store and bought a male with smooth, black fur and a female with rough, white fur. She wanted to study inheritance of those features and was sorry to see that the first litter of 8 contained only rough, black furred individuals. To her disappointment, the second litter from those same parents contained seven rough, black furred individuals. Soon the first litter had begun to produce F2 offspring. Before long the child had the following 125 F2 guinea pigs: 8 smooth, white coats; 25 smooth, black coats; 23 rough, white coats; and, 69 rough, black coats. Using the alleles A or a for fur color and B or b for fur texture, give as complete as possible the genotypes for the parental generation, the F1 generation, and the F2 generation.

Explanation / Answer

Let A be the allele for fur colour and B be the allele for texture.Let Black colour(A_) be dominant over White color(aa) and Rough texture(B_) be dominant over Smooth(bb) texture.

Parental Generation:                              Black smooth male x White Rough female

AAbb x aaBB

F1 Generation:                                The first litter of 8 contained only rough, black furred individuals.

AaBb

F2 Generation:                                       AaBb   x AaBb   (Selfed)

Phenotypic Ratio is 9:3:3:1

Black : White

25+69 : 8+23 =94:31 =3:1 (approx)

Rough : Smooth

23+69 : 8+25 = 92:33 =3:1 (approx

AB aB Ab ab AB AABB AaBB AABb AaBb aB AaBB aaBB AaBb aaBb Ab AABb AaBb AAbb Aabb ab AaBb aaBb Aabb aabb

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