Baldness, Hb, is dominant in men but recessive in women. The normal gene, Hn, is dominant in females, but recessive in males.
a. Explain how an offspring who will be bald later in life can be produced from the mating of a normal female with a normal male.
In order to understand how an offspring who will be bald later in life can be produced from the mating of a normal female with a normal male, we need to first understand the inheritance patterns of baldness.
Baldness (Hb) is a dominant trait in men, meaning that if a man carries the Hb gene, he will exhibit the trait. On the other hand, in women, baldness is recessive, which means that two copies of the Hb gene are required for a woman to be bald. The normal gene for hair density (Hn) is dominant in females, but recessive in males.
Let's now consider the mating of a normal female (HnHn) with a normal male (HnHn). Each parent contributes one allele to the offspring, leading to four possible combinations of Hb and Hn alleles: HbHn, HbHn, HnHn, and HnHn.
Since baldness (Hb) is dominant in men, if the male offspring receives an Hb allele from the father (HnHb), they will exhibit baldness later in life because the presence of the Hb allele overrides the Hn allele. However, if the male offspring receives two copies of the normal hair density gene (HnHn), they will not be bald.
On the other hand, for female offspring, baldness is recessive. Therefore, for a female offspring to be bald, they need to inherit two Hb alleles (HbHb) – one from each parent. Since the normal female (HnHn) does not carry the Hb allele, there is no chance for the offspring to inherit two Hb alleles. Consequently, a female offspring resulting from the mating of a normal female with a normal male will not be bald, as she will have one copy of the dominant Hn allele.
In summary, an offspring who will be bald later in life can only be produced if they receive the Hb allele from their father, and in the case of a male offspring. Since the normal female does not carry the Hb allele, there is no chance for a female offspring to be bald in this scenario.