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
Answer: A
Biology & Microbiology
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