In humans, curly hair is dominant to straight hair. Two curly haired parents hav
ID: 141544 • Letter: I
Question
In humans, curly hair is dominant to straight hair. Two curly haired parents have a straight haired daughter. Assume 100% penetrance and complete dominance. Please explain how you got the answer
What is the probability that the next child will be a straight haired son?
A. 0.75
B. 0.50
C. 0.375
D. 0.25
E. 0.125
What is the probability that a possible third child will be a curly haired daughter?
A. 0.75
B. 0.50
C. 0.375
D. 0.25
E. 0.125
What is the probability that if the parents have 3 children, all will be straight haired? Remember, they already have a straight haired child.
A. 0.50
B. 0.375
C. 0.25
E. 0.125
0.0625
What is the probability that if the parents have 3 children, the younger two will be both curly haired? Remember, they already have one straight haired child.
A. 0.75
B. 0.5625
C. 0.375
D. 0.25
E. 0.125
Explanation / Answer
Lets just denote the symbol "C" for curly hair and "S" for straight hair and Curly trait is dominant to straight trait.
Two curly haired parents have straight haired daughter that means the parents are heterozygous for the trait which is "CS"
Father Mother
Genotype CS X CS
Gametes C S C S
Progeny CC CS CS SS
Curly Curly Curly Straight
Probability of having a curly haired child=3/4
Probability of having a straight hair child=1/4
1. The probability of having a boy or girl will be equal to 1/2
So,
The probability of next child will be a straight haired son is 1/4*1/2=0.125
2. The probability of third child will be a curly hair daughter =3/4*1/2=0.375
The probability each time would be the same no matter what was the genotype of first child, it doesn't affect the probability of genotype of third child and so on.