pedigrees

Question 1

a colour blind boy has parents who both have normal colour vision. determine the genotype of his parents and produce a genetic cross to illustrate tour answer.

Answer 1

see diagram

Question 2

what are three things to look for when looking for evidence of sex linkage?

Answer 2

• look for much greater numbers of affected males than females, or no affected females at all (note there have to be lots of offspring to be confident)
• affected mother with a normal son - this cannot happen if the gene is a sex linked recessive one (son would also be affected because he would inherit X with recessive allele from mother and Y from father
• affected daughter with normal father - this cannot happen if the gene is sex linked and recessive (daughter would be normal as she would inherit X with dominant allele from her father)