Question

3. Round shells is incompletely dominant to square shells, the heterozygous combination is a pointed shell. Smelly
shell's is an X-linked trait and recessive. A pointed shell smelly shelled male is crossed with a round
heterozygous non-smelly shelled female. What's the phenotype of their offspring?

Answer 1

Answer:

    2/16  rounded not smelly females, RRX+X-

    2/16  pointed not smelly females, RrX+X-

    2/16  rounded smelly females, RRX-X-

    2/16  pointed smelly females, RrX-X-

    2/16  rounded not smelly males, RRX+Y

    2/16  pointed not smelly males, RrX+Y

    2/16  rounded smelly males, RRX-Y

    2/16  pointed smelly males, RrX-Y

Explanation:

Available data:

• RR round shell
• rr square shell
• Rr Pointed shell
• X+ is dominant and codes for not smelly
• X- is recessive and codes for Smelly

Cross: A pointed smelly shelled male with a round  heterozygous non-smelly female

Parentals) Rr X-Y    x     RRX+X-

Gametes) RX-, RY, rX-, rY

                RX+, RX+, RX-, RX-

Punnett square)    RX-            rX-           RY           rY

                 RX+    RRX+X-    RrX+X-    RRX+Y    RrX+Y

                 RX+    RRX+X-    RrX+X-    RRX+Y    RrX+Y

                 RX-     RRX-X-     RrX-X-     RRX-Y     RrX-Y

                 RX-     RRX-X-     RrX-X-     RRX-Y     RrX-Y

F1) 2/16 bivalves are expected to be rounded not smelly females, RRX+X-

    2/16 bivalves are expected to be pointed not smelly females, RrX+X-

    2/16 bivalves are expected to be rounded smelly females, RRX-X-

    2/16 bivalves are expected to be pointed smelly females, RrX-X-

    2/16 bivalves are expected to be rounded not smelly males, RRX+Y

    2/16 bivalves are expected to be pointed not smelly males, RrX+Y

    2/16 bivalves are expected to be rounded smelly males, RRX-Y

    2/16 bivalves are expected to be pointed smelly males, RrX-Y