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Genetics question - help please!

Q2bii - the genetic cross:
https://pmt.physicsandmathstutor.com/download/Biology/A-level/Topic-Qs/OCR-A/6-Genetics-Evolution-and-Ecosystems/6.1-Genetics-and-Evolution/Set-B/Patterns%20of%20Inheritance%203%20QP.pdf

mark scheme! - https://pmt.physicsandmathstutor.com/download/Biology/A-level/Topic-Qs/OCR-A/6-Genetics-Evolution-and-Ecosystems/6.1-Genetics-and-Evolution/Set-B/Patterns%20of%20Inheritance%203%20MS.pdf

I'm confused as to why the y is not carrying an allele - I know that sometimes, because it is smaller, it will not have an allele, but I'm not sure how you were meant to know it didn't have one in this question. Is it always the case that the y chromsome will not have an allele? (or is that not even what the dash next to the Y means?!!)

Could someone please help? Thank you :smile:

Reply 1

SweetSummerx

Original post by jsjsjsjs333

I think you are right that the - means no allele. As for how to tell whether Y will have an allele or not I think they will tell you in the question if it did as I think it’s more likely it won’t than will. Especially as eye colour is not an essential requirement to life which is what pseudoautosomal region contains. This is the region that contains many genes essential to life so you will have two copies of.

https://ghr.nlm.nih.gov/chromosome/Y