A blonde woman whose parents had black hair marries a black-haired man whose mother has blonde hair and his father black. The only child in this family is blonde. What was the probability of the appearance in the family of a child with exactly this hair color, if it is known that the gene for black hair dominates over the gene for light hair?
Let’s designate the dominant gene for black hair – A, and the recessive gene for blonde hair – a.
Even if a blonde woman had parents with dark hair – her genotype is aa, the recessive gene appears only in homozygote. The dark-haired man inherited the gene for dark hair from his father, since his mother was blonde and, therefore, passed on to him the gene – a. So the man’s genotype is Aa.
RR w aa x m Aa
g a A a
F Aa (h) aa (s)
Answer: The probability of giving birth to another blonde child in this family is 50%.
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