Show a cross between a colour blind man and a carrier woman. Write phenotype and genotype for the same
Answers
Answer:
Colour blindness is a common hereditary (inherited) condition which means it is usually passed down from your parents.
Red/green colour blindness is passed from mother to son on the 23rd chromosome, which is known as the sex chromosome because it also determines sex. Chromosomes are structures which contain genes – these contain the instructions for the development of cells, tissues and organs. If you are colour blind it means the instructions for the development of your cone cells are faulty and the cone cells might be missing, or less sensitive to light or it may be that the pathway from your cone cells to your brain has not developed correctly.
For the sake of simplicity we refer to a colour blind ‘gene’ but this is not strictly a true description. For detailed information on the genetics of colour vision deficiency, follow this link to Genevolve. At pages 5 and 6 of the CVD Sample Report there is an excellent explanation of the genetics which lead to CVD.
The 23rd chromosome is made up of two parts – either two X chromosomes if you are female or an X and a Y chromosome if you are male. The faulty ‘gene’ for colour blindness is found only on the X chromosome. So, for a male to be colour blind the faulty colour blindness ‘gene’ only has to appear on his X chromosome. For a female to be colour blind it must be present on both of her X chromosomes.