A colour blind daughter therefore must have a father who is colour blind and a mother who is a carrier (who has also passed the faulty ‘gene’ to her daughter).If her father is not colour blind, a ‘carrier’ daughter won’t be colour blind.
For the sake of the following explanation a normal X chromosome is shown as (X) whilst a colour blind carrying X chromosome is shown in bold ().
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.
If a woman has only one colour blind ‘gene’ she is known as a ‘carrier’ but she won’t be colour blind.
When she has a child she will give one of her X chromosomes to the child.