Congenital deafness in humans is due to the homozygous condition of either or both of the recessive

genes d or e. 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. Give the phenotypic results of the following crosses:
(a) Dd EE ? Dd EE
(b) Dd Ee ? Dd Ee
(c) dd EE ? DD ee
(d) Dd EE ? Dd ee
(e) Dd EE ? DD Ee What will be an ideal response?


(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

Biology & Microbiology

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