17.2 — dihybrid inheritance

Question 1

what is a dihybrid cross?

Answer 1

unlike monohybrid crosses, which show the inheritance of one gene with two alleles, dihybrid crosses shoe the simultaneous inheritance of two genes controlling separate characteristics.

Question 2

what can dihybrid crosses help to do? (3)

Answer 2

1. determine whether genes are linked
2. locate genes of specific chromosomes
3. calculate expected phenotypic ratios in subsequent generations

Question 3

what are the reasons for deviations from expected phenotypic ratios? (2)

Answer 3

1. random fertilisation
   — gamete fusion is a chance process
   — small sample sizes can lead to skewed rations, while larger samples minimise these random effects
2. linked genes
   — linked genes are on the same chromosomes so alleles are usually inherited together, maintaining the parents allele combinations
   — however, crossing over during meiosis can sometimes change these allele combinations by separating linked genes