Colourblindness:
It is a hereditary eye disease. It was first described by Horner. It is of 2 types –
1. Red-green colourblindness
2.Blue colourblindness .
- The red-green colourblindness is most common & it is also called a proton defect.
- Red-green colourblindness is caused due to the absence of red-green cones in the retina.
- The person is unable to identify red, green, yellow & orange colours. These colours appear to be green in the absence of red cones and they appear to be red in the absence of green cones.
- It is a sex-linked disease which is caused due to a recessive gene on the x-chromosome. The mother (female) acts as a carrier.
- The father of a colourblind daughter is always colourblind.
- In the F1 generation of carrier mother & normal father, 50% generation will be normal, 25% will be carrier & 25% will be colourblind.
- In F1 generation of carrier mother and colourblind father, 50% of daughters will be colourblind & 50% will be carrier likely, 50% of boys will be normal & 50% will be colourblind.
- In the F1 generation of normal mother & colourblind father, all males will be normal and all daughters will be a carrier.