English

Sex-Linked Inheritance in Human Beings - Colour blindness

Topics

Estimated time: 3 minutes

CISCE: Class 12

Definition: Colour Blindness

Colour blindness is an X-linked recessive hereditary disorder in which a person is unable to distinguish between red and green colours due to the presence of a defective gene on the X-chromosome.

Maharashtra State Board: Class 12

Key Points: Colour Blindness

Meaning: Colour blindness is an X-linked recessive disorder in which a person cannot distinguish between red and green colours.
Cause: It is caused by a recessive gene (Xᶜ) that prevents the formation of colour-sensitive cone cells in the retina.
Expression in Sexes: Males (XᶜY) are more commonly affected, while females are affected only if both X chromosomes carry the recessive gene (XᶜXᶜ); otherwise, they act as carriers (XᴄXᶜ).
Inheritance Pattern: It shows criss-cross inheritance, where the gene passes from father to daughter (carrier) and then to grandson.
Example Crosses: Colour blind male × normal female produces carrier daughters; carrier female × normal male produces 50% colour blind sons.