Heterozygous red-eyed White-eyed

Female male

P1 R r X r

XX XY

G1

R r R r r r

F1 XX XY XX XY

Red-eyed Red-eyed White-eyed White-eyed

female male female male

25% 25% 25% 25%

Sex-linked characteristics in Man:

The linkage of some characteristics with sex is common among livings. In Man, both Colour blindness (the inability to distinguish red from green) and Haemophilia (lack of blood clotting factors) are sex-linked diseases.

Pedigree studies indicated that these two characteristics are recessive and rarely occur in females. Sex linkage follows the same system as that seen in case of colour of eyes in Drosophila:

- The female passes these traits to her sons.

- The sick male passes these traits to his grandsons through his daughters.

- Sons inherit the sex linked gene from their mothers.

- Sex-linked trait (as Colour blindness and Haemophilia) appears in daughters when they gain this gene from both parents (this requires that the mother should be a carrier, whereas the father would have colour blindness).