Zb

So, % of the F2 are barred males, % are nonbarred males, % are barred females, and % are nonbarred females.

F1 red

The F1 are then intercrossed to produce the F2. Whenever two individuals heterozygous for an autosomal recessive characteristic are crossed, 3/4 of the offspring will have the dominant trait and % will have the recessive trait; thus, 3/4 of the F2 flies will have red eyes and % will have brown eyes:

F1 red eyes red eyes

V4 bb brown y4 red, % brown

Next, we work out the results for the X-linked characteristic. A female that is homozygous for normal bristles (X+X+) is crossed with a male that has forked bristles (XfY). The female F1 from this cross are heterozygous (X+Xf), receiving an X chromosome with a normal-bristle allele from their mother (X+) and an X chromosome with a forked-bristle allele (Xf) from their father. The male F1 are hemizygous (X+Y), receiving an X

ZBZb

ZbW

barred

nonbarred

male

female

ZBZb

ZbW

barred

nonbarred

male

barred female

ZbZb nonbarred male

nonbarred female

chromosome with a normal-bristle allele from their mother (X+) and a Y chromosome from their father:

X+X+ X'Y normal X forked P bristles bristles

Fj J/2 X+Xr normal bristles

J/2 X+Y normal bristles

When these Fj are intercrossed, J/2 of the F2 will be normal-bristle females, J/4 will be normal-bristle males, and J/4 will be forked-bristle males:

Gametes

0 0

Post a comment