Question

A teacher prepared a dihybrid cross Punnett square and a key to dominant and recessive traits.

Answer 1

Answer and Explanation:

There are four phenotypes: tall, short, round, wrinkled

Let us say that for the high trait, tall dominates over short. For the shape trait, round dominates over wrinkled. This is:

• T allele determines tall plants
• t allele determines short plants
• R allele determines rounded seeds
• r allele determines wrinkled seeds.

The fact that parental are dihybrid, tells us that their genotypes were TtRr

Cross:

Parental)        TtRr          x         TtRr

Gametes) TR tR Tr tr           TR tR Tr tr

Punnet Square)     TR           tR           Tr          tr

                  TR      TTRR     TtRR     TTRr       TtRr

                   tR      TtRR      ttRR       TtRr        ttRr

                   Tr      TTRr      TtRr       TTrr         Ttrr

                   tr       TtRr       ttRr        Ttrr           ttrr

F1)         Genotype    and    Phenotype

•      1/16 TTRR              Tall, round
•      2/16 TtRR              Tall, round
•      2/16 TTRr              Tall, round
•      1/16 ttRR                Short, round
•      4/16 TtRr               Tall, round
•      2/16 ttRr                Short, round
•      1/16 TTrr                Tall, wrinkled
•      2/16 Ttrr                Tall, wrinkled
•      1/16 ttrr                   Short, wrinkled

Phenotypic proportions  

•    9/16 Tall, round
•    3/16 Tall, wrinkled
•    3/16 Short, round
•    1/16 Short, wrinkled