Dihybrid Testcrosses In the following crosses, the wild trait is dominant and th

Question

Dihybrid Testcrosses

In the following crosses, the wild trait is dominant and the brown trait for eye color and ebony trait for body color are both recessive. You will compare the offspring of homozygous wild flies to the offspring of heterozygous wild flies, when each is crossed with a recessive brown-eyed fly with an ebony body.

Note:  Genetic notation: In fruit fly genetics, the normal fly is called a "wild type" and any flyexhibiting a phenotypic mutation is called a "mutant". Mutant flies are given names that generally denote the type of mutation the fly exhibits.

7. Perform a monohybrid cross between a wild-type female fly and a male fly with brown eyes and ebony body.
Show results for the F1 offspring. (NOTE: You will use one of these F1 flies in the next cross.)
ENTER DATA HERE:

PUNNETT SQUARE:

            List the genotypes of the flies in this cross:

            List the gametes produced by each fly in this cross:

            Show the Punnett Square for the above cross.

Question: By examining the offspring, determine whether the wild-type female parent was homozygous or heterozygous for eye color and body color. How did you arrive at this conclusion?

Question: Are the F1 offspring homozygous or heterozygous for eye color and body color? How did you arrive at this conclusion?

Explanation / Answer

Eye colour- dominant red(R), recessive brown(r)

Body colour- dominant yellow(Y), recessive ebony(y)

We have to cross each, RRYY(homozygous dominant) and RrYy(heterozygous dominant) with rryy(recessive)

1. RRYY(homozygous dominant)

Gametes- only RY from wild

only ry from mutant

so, RY crossed with ry gives only

RrYy (all are homozygous dominant)

that is, all offsprings have red eyes and yellow bodies.

2. RrYy(heterozygous dominant)

Gametes- RY, Ry, rY, ry

Crossing,

RrYy

Red eyes and yellow bodies

Rryy

Red eyes and ebony body

rrYy

brown eyes and yellow body

rryy

brown eyes and ebony body

so various combinations are seen in equal percentages(25% each).

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