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?
Question 2In poultry, the genes for rose comb (R) and pea comb (P) produce walnut whenever they occur
together (R_ P_); single-combed individuals have the homozygous condition for both genes (rr pp).
(a) Give the F1 and F2 phenotypic results of a cross of a pure-breeding rose comb (RR pp)
with a pure-breeding pea comb (rr PP).
(b) Give the phenotypic results of a cross of Rr Pp rr Pp.
(c) Give the phenotypic results of a cross of RR Pp rr Pp.
(d) Give the phenotypic results of a cross of Rr pp rr Pp.
(e) Give the phenotypic results of a cross of Rr Pp rr pp. What will be an ideal response?
Quick Reply
