Question

If a colour blind woman marries a normal visioned man, their son would be?

Answer 1

Hint: Colour blindness is a recessive sex linked disorder. Sex linked disorder is due to a defective allele present over a sex chromosome. The alleles situated on the X- chromosome show criss- cross inheritance while Y-linked alleles directly pass to the male offspring. Being hemizygous, males are more prone to sex -linked disorder.

Complete answer:
In this disorder, the patient cannot distinguish red-green colours. There are two types of cells in the retina, rod cells and cone cells. Rod cells detect only light and dark and are sensitive to low light levels. Cone cells detect colour and are concentrated near the center of vision. Three types of cones are : red, green and blue. Input from these cone cells is sent to the brain to determine our colour perception. Colour blindness can happen when one or more of the cone cells are absent, or not working.
The defect is not lethal in a homozygous state. Therefore, it occurs in women also. Hemizygous condition is enough for the occurrence of defects in males. The famous scientist Dalton suffered from the disorder. Because of his association with the genetic defect, red-green colour blindness is also known as Daltonism. The genetic base of this disorder was studied by Horner (1876). Colour blindness is actually of three types. (i) Protanopia-red colour blindness. (ii) Tritanopia-blue colour blindness. (iii) Deuteranopia-green colorblindness.
Tritanopia is rare and generally caused by drug toxicity, retinal detachment and disorders of the nervous system. The other two, protanopia and deuteranopia, are caused by defective heredity that produces defects in cones specialised to perceive red and green colours. Ishiara cards are used for diagnosis of colour blindness.
Marriage between a normal visioned man (XY) and colour blind women (X*X*) will result in carrier daughters and colour blind sons.

Note:
Each cone is sensitive to either blue, green or red light (short, medium or long wavelengths). The cones recognized these lights based on their wavelength. Pigments inside the cones register different colours and send information through optic nerves to the brain. This enables us to distinguish countless shades of colours.