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Two genes determining a trait In primroses, the dominant allele of gene K is necessary to synthesize blue flower pigment. Blue pigment synthesis is inhibited by a dominant allele of gene D. In other words, plants with the genotype K- D- will not produce pigment (and their flowers will be white) because of the presence of the D allele. If you set up a testcross for (Kk Dd) plants what is the ratio of blue to white offspring in the progeny?

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marianaegarciaperedo

Answer:

The ratio of blue to white offspring in the progeny is 4 blue : 12 white.

Explanation:

Available data:

  • The dominant allele K is necessary to synthesize blue flower pigment
  • K is inhibited by the dominant allele D
  • Plants with the genotype K- D- will not produce pigment (and their flowers will be white)

Cross: testcross for (Kk Dd) plants

Parental)   KkDd     x     kkdd

Gametes) KD   kD   Kd   kd      

                kd   kd   kd   kd

Punnet square)        KD        Kd       kD       kd

                      kd     KkDd   Kkdd   kkDd   kkdd

                      kd     KkDd  Kkdd   kkDd   kkdd

                      kd     KkDd   Kkdd   kkDd   kkdd

                      kd     KkDd   Kkdd   kkDd   kkdd

  • Whenever D is present, it inhibits the expression of the K gene, so every plant with the dominant D allele will be white. This plants´ genotype is kkD- or K-D-.
  • Whenever D is absent and K is present, every plant with genotype K-dd will be blue.
  • The recessive form for K and D genes will express white-flowered plants, with genotype ddkk

F1) Progeny genotype: 4/16 KkDd, white-flowered plants

                                      4/16 Kkdd, blue-flowered plants

                                      4/16 kkDd, white-flowered plants

                                      4/16 kkdd, white-flowered plants

     The ratio of blue to white offspring in the progeny is 4 blue : 12 white.

     Blue-flowered plants: 4 Kkdd

     White-flowered plants: 4 KkDd + 4 kkDd + 4 kkdd

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