Testcross

1) You have been given three plants: two produce solid black orchids, and one has grey petals. You cross each black-flowered plant to the grey plant with the following results

Parents                          F1

black #1 X grey           87 solid black, 83 spotted black

black #2 X grey            all black

You cross the solid black-flowered F1 plants from cross #2 with the following results in the F2:132 black35 spotted black11 greyDevise the best genetic explanation for these results.

How many genes are involved in these phenotypes?

2) Horses can be cremello (light cream color), chestnut (a brownish color) or palomino(golden color with white in the horse’s tail and mane). Of these phenotypes, only palominos never breed true.

Parents                                                F1 Progeny

(A) Cremello x Palomino                     1/2 cremello & 1/2 palamino

(B) Chestnut x Palomino                     1/2 chestnut & 1/2 palomino

(C) Palomino x Palomino                     1/4 chestnut, 1/4 cremello, 1/2 palomino

How many genes are involved in these results?

3)  You have isolated a pure breeding strain of flies with black bodies (strain #1). The black allele is recessive to the wild-type brown allele. Another lab has also isolated a pure breeding strain with a recessive black allele (strain #2). You cross males from your strain #1 with females from strain #2. All of the F1 progeny have wild-type brown bodies. You cross the F1 sons and daughters to each other and see the following F2 progeny:

366 brown

274 black

(640 total offspring)

How many genes are involved in these crosses?

4) In a cross of Rr X Rr, what is the chance of getting 5 rr plants?[enter your answer as a fraction such as 1/9 or 1/100000]

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