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In snapdragons, red flower color is incompletely dominant to white, with the heterozygote being pink; normal flowers are completely dominant to symmetrical flowers; and tallness is completely dominant to dwarfness. The three gene pairs segregate independently. If a true-breeding white, tall, normal-flowered plant is crossed to a true-breeding red, dwarf, symmetrical flowered one, what proportion of the F2 plants will resemble the F1 plants in phenotype

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marianaegarciaperedo

Answer:

9/32 Pink, Tall and Normal individuals Rr Tt Nn

Explanation:

Available data:

  • Red color RR
  • Pink color Rr
  • White color rr
  • Normal NN and Nn
  • Symmetrical nn
  • Tall TT and Tt
  • Dwarf tt

1st Cross:

Parental) rr TT NN   x   RR tt nn

F1) 100% RrTtNn

2nd Cross:

Parental) Rr Tt Nn   x   Rr Tt Nn

Knowing that these three genes assort independently, then we can infer that the F2 will have the next phenotypic proportions for each gene:

RR= 1/4 Red

Rr= 2/4  Pink

rr=1/4  White

TT + Tt= 3/4  Tall

tt=1/4 Dwarf

NN + Nn = 3/4 Normal

nn=1/4 Symmetrical

  • The proportion of the F2 plants that will resemble Rr Tt Nn (Pink, tall, Normal) in Phenotype

Rr= 2/4 pink

TT + Tt= 3/4  Tall

NN + Nn = 3/4 Normal

2/4  x  3/4  x  3/4 = 18/64= 9/32    

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