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