Dihybrid inheritance

Question 1

What are dihybrid crosses used to show?

Answer 1

• the inheritence of two genes
• this is known as dihybrid inheritence
• two different characteristicts
• which may be located on different pairs of homologous chromosomes

Question 2

How is a dihybrid cross?

Answer 2

• very similar format to the one used when studying a monohybrid cross
• four alleles (two for each characteristic) are shown at each stage instead of two
  
  • e.g Xy, xy against xY, xy
  • depends on the possible gametes of the F1 generation

Question 3

Why may the actual ratio of offspring produced can differ from the expected?

Answer 3

• the fertilisation of gametes is a random process
  
  • so in a small sample a few chance events can lead to a skewed ratio
• the genes being studies are both on the same chromosomes
  
  • these are known as linked genes
  • if no crossing over occurs the alleles for the two characteristics will alway be inherited together

Question 4

WHat is the expected ratio when all 4 possible gametes and plotted against all 4 gametes?

(XY, Xy, xY, xy)

Answer 4

9:3:3