Question

1. Hemophilia is a sex-linked recessive disorder. If a male hemophiliac has children with a woman who is homozygous normal (has no family history of the hemophilia trait), what percentage of his male children would be hemophiliac (so, ignore the females)

(a) 50% (1/2)

(b) 100% (2/2)

(c) 0% (0/2)

2. To perform a test cross, you cross an organism with a

a. homozygous dominant

b. homozygous recessive

c. heterozygote

Answer 1

1.-

The percentage is c = 0%
As stated the hemophiliac gen is sex-dependent, meaning it is carried either in the x or y chromosome, since there are hemophiliac girls we know the gen is in the X chromosome.

We also know that in reproduction the males provide either the Y chromosome for male descendants or the other X chromosome for female descendants and that the Female provides the X chromosome for either males or female descendants.

So in the case of the coupling of a male hemophiliac and a normal female the sons would not be carrying the hemophiliac gen as the mother provides the X chromosome.

I XXXXY X XX XY

But any girl would be a carrier

2.-

A test cross is performed whit :

b. homozygous recessive organism

A test cross is a way to find out the genotype of an individual because you are crossing it what a known genotype the resulting offspring can let you know the genotype of the individual.

if the unknown genotype gives an offspring whit the same characteristics as itself we could guess it is a homozygous dominant

if the unknown genotype gives an offspring whit the same characteristics as the homozygous recessive we could guess it is also a homozygous recessive

if instead the unkown genotype gives an ofspring whit mix characteristics e could guess it is a heterozygot

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