Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cactuses have dull spines. At the same time, a second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. If doubly heterozygous SsNn cactuses were allowed to self-pollinate, the F2 would segregate in which of the following ratios?

Answer and Explanation:

Available data:

Cross: Doubly heterozygous SsNn individuals allowed to self-pollinate

Parental)   SsNn     x     SsNn

Gametes) SN   sN   Sn   sn   /   SN   sN   Sn   sn

Punnet square)     SN          Sn        sN        sn

                 SN       SSNN     SSNn    SsNN   SsNn

                 Sn        SSNn      SSnn    SsNn    Ssnn

                 sN        SsNN      SsNn    ssNN   ssNn

                 sn         SsNn      Ssnn     ssNn    ssnn

        Their genotypic ratios are 1/16 SSNN, 2/16 SSNn, 2/16 SsNN, 4/16    

        SsNn

        Their genotypic ratios are 1/16 ssNN and 2/16 ssNn

        Their genotypic ratios are 1/16 SSnn, 2/16 Ssnn, and 1/16 ssnn.    

genetic variation will increase because of a new habitat and food source.

explanation:

the law of original horizontality explains:   why rocks appear in layers. correct answer: b the law suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed.   the principle is used by geologists to make assumptions about the relative ages of sedimentary rocks.