Biology · May / June 2020 · Paper 41 · Question 6
0610
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Colour blindness is a characteristic that is inherited. Colour blindness is more common in males than in females. Fig. 6.1 is a pedigree diagram showing the inheritance of colour blindness in a family. 1 2 3 5 6 7 8 4 male with normal colour vision male with colour blindness female with normal colour vision Key: Fig. 6.1
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6(a)[1]
transmission of genetic information from generation to generation ;
6(b)(i)[3]
1 correct use of X and Y in responses for individual 5 and individual 8 ;
2 correct X allele given for individual 5: XbY / b ;
3 correct X allele given for individual 8: XBY / B ;
6(b)(ii)[3]
any three from:
colour blindness is a sex-linked characteristic ;
she is, heterozygous for the gene / Bb ;
she has, normal allele / B, so has normal colour vision ;
but has passed on the, recessive allele / b, to her sons / 5 and 7 ;
she has two X chromosomes which have the gene for colour vision ;
father / 4, passes on his Y chromosome ;
6(b)(iii)[2]
any two from:
mutation ;
to give, recessive allele / b ;
occurred in 3 or in one of her parents / 1 or 2 or her grandparents ;
AVP ; e.g. other reason such as donated gamete
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