In the exam, it is quite frequent to see questions asking you to determine whether a given inherited condition is sex-linked or not. 😲
Lets go have a look on an example here selected from a public exam paper.... 👀
How should we approach these types of questions? 👆
Here is the key to crack it :
As you can see, whenever the exam is asking you whether the gene/inheritance is sex-linked or not, always always always look up for the "recessive mum" and " her sons". 👨👩👦
If the inheritance is sex-linked, this would suggest the "recessive mum" is possessing both X chromosomes carrying the recessive allele.
And we know the X chromosome of the son IS ALWAYS AND MUST come from his mother.
Hence this would suggest all her "sons" shall CARRY and EXPRESS the recessive allele.
If not, it is not sex-linked. Thats how easy it is! 😉
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