Deduce with reasons for your answer, whether the chromosomes are autosomes or sex chromosomes.

Deduce with reasons for your answer, whether the chromosomes are homologous or non-homologous.   

State the stage of meiosis of a cell if it contains pairs of chromosomes as shown in the diagram.

Determine the combinations of alleles that would be present on each chromatid. Use the diagrams to indicate your answer.

State the pattern of inheritance shown by the three genes.

autosomes because the sex chromosomes/X and Y chromosomes would be different lengths/sizes / would have different genes

homologous because they have paired/formed a bivalent / tetrad / there is crossing over between the chromosomes / they have the same genes (in the same sequence) / they are the same size and shape

first prophase/first metaphase/prophase I/metaphase I

Allow [1] only if the C allele is not on the short arm or the A and B alleles are not on the long arm. Use a maximum of two ticks in your marking.

(gene) linkage / autosomal linkage

For question 3 a (i) and (ii) Too many were just guessing and, even if correct, did not give a reason.  Many argued that crossing over does not occur in sex chromosomes.  A failure to use the introductory information “in the human testis” caused a problem for many.  

For question 3 a (i) and (ii) Too many were just guessing and, even if correct, did not give a reason.  Many argued that crossing over does not occur in sex chromosomes.  A failure to use the introductory information “in the human testis” caused a problem for many.  

Although this was most commonly answered correctly, there were a surprising number that did not know what should have been a very straightforward bit of factual knowledge.

This was quite commonly answered correctly though many candidates should be advised to take greater care in the construction of lower case and upper case letters in genetics problems.

A surprising number indicated polygenic inheritance showing conceptual misunderstanding.