Congenital deafness in humans is due to the homozygous condition of either of the recessive alleles d or e,or both.Both dominant D and E are necessary for normal hearing.Gene D/d affects the middle ear,while gene E/e affects the inner ear.It does not matter how good the normal inner ear (as indicated by E__)is; if there is something wrong in the middle ear,the individual is unable to hear.The same applies for the other gene.What is the phenotypic result of the cross Dd EE x Dd EE?
A) 3/4 normal, 1/4 deaf
B) 9/16 normal, 7/16 deaf.
C) all normal
D) 3/4 normal, 1/4 deaf..
E) all normal.

Question

Congenital deafness in humans is due to the homozygous condition of either of the recessive alleles d or e,or both.Both dominant D and E are necessary for normal hearing.Gene D/d affects the middle ear,while gene E/e affects the inner ear.It does not matter how good the normal inner ear (as indicated by E__)is; if there is something wrong in the middle ear,the individual is unable to hear.The same applies for the other gene.What is the phenotypic result of the cross Dd EE x Dd EE?  
A) 3/4 normal, 1/4 deaf
B) 9/16 normal, 7/16 deaf.
C) all normal
D) 3/4 normal, 1/4 deaf..
E) all normal.

Quizplus · Accepted Answer

Given that both dominant alleles D and E are necessary for normal hearing, and each parent is heterozygous for D (Dd) but homozygous dominant for E (EE), the offspring will inherit the E allele from both parents, ensuring normal inner ear function. However, the Dd x Dd cross for the middle ear gene follows a Mendelian inheritance pattern, resulting in a 3:1 ratio of normal hearing (DD or Dd) to deaf (dd). Therefore, 3/4 of the offspring will have normal hearing, and 1/4 will be deaf due to the homozygous recessive condition (dd) affecting the middle ear.

Congenital Deafness in Humans Is Due to the Homozygous Condition