Question

The genes for sex-linked traits are carried on either the X or Y chromosome. Duchenne muscular dystrophy (DMD) is a recessive, sex-linked disease that is carried on the X chromosome. A woman with DMD and a man without the disease have a child. Which statement best describes the likelihood of the disease passing to their child?

Answer 1

@blues
wud this be like the same process from the last one

Answer 2

It is very similar to the last one.

We started the last one by assigning a notation or naming the alleles, then using those letters to write out the parents' genotypes. Want to give it a try?

Answer 3

so like X and x

Answer 4

Hmm, X will work - but because an entire chromosome is also named X, it might get confusing. Usually people pick a letter close to the name of the gene. Personally, I would pick d or D for "Duchenne Muscular Dystrophy" but that is just personal taste...

Answer 5

so D and d will work

Answer 6

So using D and d, what are the parents' genotypes?

Answer 7

this is where i got a little confused... since DMD is a recessive trait does that mean the mother who passed it on was dd and the dad was DD?

Answer 8

This is where it is more detailed than the last question because in this question, the gene is on sex chromosomes. Mom (female) has two X chromosomes, Dad (male) has one X and one Y.

The mother who passed it on definitely has two X chromosomes, so she will have two alleles for the disease. And because she has the disease, they are definitely recessive alleles, dd.

Dad is more complicated. He has one Y and one X. Only the X can have the gene. And we know that he does *not* have Duchenne Muscular Dystrophy. So that X chromosome has to have the dominant allele. So he is YD.

That is why we are working with D and not X. :)

Answer 9

so how would this punnet square look..?

Answer 10

Mom's genotype is dd, Dad's genotype is YD. You would set up the Punnett the same way you set up the Punnett in the first problem. Would you like to draw it or shall I?