Page 15 - Lesson Notes- Principle of inheritance & Variation

They are transmitted into
They are transmitted as the affected individual is
generations through Mendelian
sterile.
principles of inheritance.

They may be recessive or dominant
This is always dominant in nature.
in nature.

Examples: Colour blindness
Examples: Downs syndrome, Turner's syndrome
Pheffykenonia.

Medelian disorder includes-

a. Haemophilia- sex linked recessive disease in which, in an infected individual, a minor cut

leads to non-stop bleeding. Heterozygous female (carrier) can transmit the disease to their son.
The possibility of a female becoming a haemophilic is extremely rare because mother of such a

female has to be at least carrier and the father should be haemophilic (unviable in the later

stage of life).

b. Sickle cell anemia- an autosome linked recessive trait in which mutant haemoglobin

molecules undergo polymerization under low oxygen tension causing change in shape of the
RBC from biconvex disc to elongated sickle like structure. The defect is caused by the

substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin

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