Pattern baldness in humans is a sex- influenced trait that is autosomal dominant
ID: 18365 • Letter: P
Question
Pattern baldness in humans is a sex- influenced trait that is autosomal dominant in males and recessive in females. Jack has a full head of hair. Jo Ann is bald. What proportion of Jack and JoAnn's children are expected to be bald?Show work and Please choose an answer:
a) all males will be bald; all females will have full hair
b) 3/4 males will be bald; 1/4 females will be bald
c)1/2 males will be bald; 1/2 females will be bald
d)1/4 males will be bald; 3/4 females will be bald
e) all males will be bald; 1/4 females will be bald
Explanation / Answer
We’ll use Hb to denote the baldness allele that is dominant in males and H+ to denote the full hair allele. Jack must be H+H+ because he has the recessive phenotype for males. JoAnn’s mother must be HbHb because she has the recessive phenotype for females. JoAnn, therefore, although she has a full head of hair, must be HbH+ because she must have inherited an Hb from her mother. A marriage between Jack and JoAnn would thus produce: H+H+ × HbH+ ? ¼ H+H+ males with full hair ¼ H+H+ females with full hair ¼ HbH+ males with pattern baldness ¼ HbH+ females with full hair Therefore, ¼ of their children will be bald.