Inheritance Question

How can you determine that the gene is carried on the X chromosome based on this data? I cannot get my head around why it HAS to be on the X chromosome for this set of data - surely there is not enough information to determine this and could have been passed on any other chromosome as it is a recessive allele and could be from any other chromosome no?

Any help in explaining this will be greatly appreciated - Thanks!

I dont think you can 100% conclusively say it is X linked but it tells you in the question and you can see that the two boys on the RHS both have the hairless phenotype which would be unlikely if it was a normal recessive allele but much more likely if it was X linked.

Generally if you look at the data and it affects boys more obviously more than girls, its likely to be X linked

So in terms of getting the mark for this question - why would the mark be given for any of these

Hairless males have fathers with hair / 4 is hairless but 1 is hairy / 7 and/or 8 are hairless but 6 is hairy / only males are hairless;

Saying that males are hairless only doesn't prove that it is X chromosome (just makes it more likely), for hairless males with fathers with hair its just as likely they would inherit a Hairy X chromosome from the mother rather than the recessive one?

The fact that they have told you it is X linked in the question allows you to use the higher probabilities to show that it is, if a gene is X linked, much higher chance of a male having it even with an unaffected father.

"X-linked recessive conditions are caused by a gene alteration on the X chromosome. As males have only one X chromosome, if they have a gene alteration on their X chromosome they will develop the condition.
Females rarely show signs of X-linked recessive conditions as they usually have a second unaltered copy of the gene on their other X chromosome to compensate for an altered gene. A female who has a gene alteration on one of her X chromosomes is said to be a carrier for the X-linked recessive condition.
Males transmit their Y chromosome to their sons. This means that sons will not inherit an X-linked recessive condition from their father."

The fact that male children of unaffected fathers and carrier mothers have it and that no females anywhere have it suggests that it is highly likely to be X linked.

If it was recessive it would show no "preference" for males over females as it clearly does from the pedigree.