Describe Mendelian Disorder.
 

Mendelian disorders are mainly determined by alternation or mutation in the single gene.

These disorders are transmitted to the offspring on the same lines as the principle of inheritance

The pattern of inheritance of Mendelian disorders can be traced in a family by the pedigree analysis.

Most common and prevalent Mendelian disorders can be traced in a family by the pedigree analysis.

Most common and prevalent Mendelian disorder are Haemophilia, Cystic fibroses, Sickle cell anaemia, Colour blindness, Phenylketonuria, Thalassemia etc.

Such Mendelian disorder may be dominant or recessive.

By pedigree analysis one can easily understand whether the trait in question is dominant or recessive.

Similarly the trait may also be linked to the sex chromosome as in case of haemophilia.

It is evident that this $X$-linked recessive trait shows transmission from carrier female to male progeny.

A representative pedigree is shown in figure for dominant and recessive traits.

Colour blindness is sex linked recessive disorder due to defect in either red or green cone of eye resulting in failure to discriminate between red and green colour.