# What is the probability that all four are normal? That three will be normal and one albino? Two normal and two albino? One normal and three albino? All four albino?

## Albinism in humans is controlled by a recessive gene (c) . From marriages between (Cc). Assume that such marriage (Cc x Cc) 4 children are produced.

May 7, 2017

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When both parents are heterozygous (Cc) carrier, in each pregnancy there is 25% chance of birth of an albino i.e. 1 in 4. So, in each pregnancy, there is 75% chance of birth of a normal (phenotypic) child i.e. 3 in 4.

Probability of birth of all normal : $\frac{3}{4} X \frac{3}{4} X \frac{3}{4} X \frac{3}{4}$ approx 31%

Probability of birth of all albino : $\frac{1}{4} X \frac{1}{4} X \frac{1}{4} X \frac{1}{4}$ approx 0.39%

Probability of birth of two normal and two albino:
$\frac{3}{4} X \frac{3}{4} X \frac{1}{2} X \frac{1}{2}$ approx 3.5%

Probability of birth of one normal and three albino:
$\frac{3}{4} X \frac{1}{4} X \frac{1}{4} X \frac{1}{4}$ approx 1.1%