# If a recessive genetic disease occurs much more frequently in men than women, which chromosome should be studied as a possible source of the disease?

Mar 1, 2018

X Chromosome

#### Explanation:

The only main difference between male/female genomes is the presence of either 2 copies of X chromosome (women), or XY chromosomes (men). If women have a problem on one X chromosome, there is a 2nd copy to help with problems (extremely simplistic view); whereas in men, if the X is problematic, then they will have a very high disease chance. All the other chromosomes are equivalent among men/women....so the sex chromosomes (X and Y) would be where you see a big difference between men and women.

Mar 1, 2018

$X$ chromosome

#### Explanation:

A recessive disease which is showing sex variation,means it is an $X$ linked recessive disease.

Now,$X$ linked recessive diseases are expressed more in men than women,as a woman has two $X$ chromosomes,one received from father and one from mother,so if she has to suffer from this disease,she needs to have both the $X$ chromosomes defective,or else the dominant normal $X$ chromosome will take the upperhand and she will become a carrier of that disease.

But,males have one $X$ chromosome only,so they are basically hemizygous,that means both the $X$ & $Y$ characters are expressed in a male.

So,if the male receives an abnormal recessive disease associated gene bearing $X$ chromosome,then the disease manifestations will must be seen in him.

So,receving for one defective $X$ chromosome, chances of a male getting affected is 100% but for a female this is 50% as,the other $X$ may be normal or abnormal.

So,disease frequency is high for males.

You can study the following pedigree made,with a normal father and mother as a carrier of colour blindness($X$ linked recessive disease)

In the image $X '$ stands for gene responsible for colorblindnes