Unearthly Linkage - Children of Mr Spock - A level Biology Challenge

Mr Spock, 2nd officer of the Starship Enterprise, has a Vulcanian father - Sarek. His mother - Amanda Grayson, is from Earth.

Vulcanians have pointed ears (P), adrenal-absent (A) and a right sided heart (R), all dominant to the human alleles.

The alleles for adrenal and heart are located on the same chromosome, while those for ear shape lie on a different chromosome.

If Mr Spock were to marry a woman from Earth, what would be the probability that?

·       Their first child would have all Mr Spock’s characters?

·       Their first child would have adrenal absent, but have human heart and ears?

·       That if they had 2 children, one would have human features and the other Vulcanian?

Autosomal linkage - Try with 3 Alleles ...- Genetics and A-level Biology

Students find autosomal linkage a challenge ... I suspect this is because they mentally disconnect Meiosis from gamete formation.

Remember that the gametes in dihybrid inheritance result from the  independent assortment of the chromosomes in metaphase I. Consequently, if alleles are on the SAME chromosome then they cannot assort independently and must be passed to the gamete together (linked)... unless they form chiasma in Prophase one and exchange parts of the maternal and paternal chromosome (crossing over).

Here is a pdf of the question and a markscheme