Question

The following pedigree shows how the gene for colourblindness was passed in a family for three generations. The gene for colour blindness is sex linked.

1. Define the term sex linkage. 
2. Write down the genotype of the parents A and B.
3. Write down the phenotypic ratios of the 2nd generation from parents A and B. Show how you arrived at your answer. 

Answer 1

1. Phenomenon where genes controlling other traits are carried in the sex chromosomes with the sex gene and are transmitted together. 
2.  
   • A- XcXc     
   • B- XcY
      
3. Write down the phenotypic ratios of the 2nd generation from parents A and B. Show how you arrived at your answer. (5mks)
   
   Genotype of 2nd generation
   Phenotypic ratio/Normal: 1 colourblind.