In humans,normal skin pigmentation is influenced by a dominant gene (C),which allows pigmentation to develop.All individuals who are homozygous for the recessive allele (c)are unable to produce an enzyme needed for melanin formation and are therefore referred to as albino.Two normal parents produce an albino child.What are the chances that the next child will be an albino?
A) 1/2 chance
B) 2/3 chance
C) 1/4 chance
D) 1/8 chance
E) no chance

Question

In humans,normal skin pigmentation is influenced by a dominant gene (C),which allows pigmentation to develop.All individuals who are homozygous for the recessive allele (c)are unable to produce an enzyme needed for melanin formation and are therefore referred to as albino.Two normal parents produce an albino child.What are the chances that the next child will be an albino?  
A) 1/2 chance
B) 2/3 chance
C) 1/4 chance
D) 1/8 chance
E) no chance

Quizplus · Accepted Answer

Since both parents are heterozygotes (Cc), they each carry one copy of the recessive allele (c) and one copy of the dominant allele (C). The Punnett square for their cross is:

|   | C | c |
|---|---|---|
| C | CC| Cc|
| c | Cc| cc|

From the Punnett square, we can see that there is a 1/4 chance (25%) of the next child being an albino (cc), since both parents have one copy of the recessive allele and there is a 1/4 chance of both copies being passed on to the next child.

In Humans,normal Skin Pigmentation Is Influenced by a Dominant Gene