8.2 Transfer of genetic information

Question 1

Explain why crossing over between two different genes, located on a pair of homologous chromosomes, results in a maximum of 50% of gametes with the recombinant alleles. (3)

Answer 1

• crossing over occurs between chromatids (between the same
  homologous chromosomes) (1)
• therefore (only) half the chromosomes (produced by anaphase II)
  will be recombinant chromosomes (so maximum of 50 %) (1)
• crossing over does not always take place (so can be less than 50 %)