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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

User Blackened
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2 Answers

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Final answer:

The F1 generation will have pink flowers as a result of the incomplete dominance between red and white flower colors. In the F2 generation, the genotypic ratio will be 1 CRCR:2 CRCW:1 CW CW, and the phenotypic ratio will be 1:2:1 for red:pink:white.

Step-by-step explanation:

The F1 generation of the cross between a white, tall, normal-flowered plant and a red, dwarf, symmetrical flowered plant will have pink flowers, as the red flower color is incompletely dominant to white. This is an example of incomplete dominance, where the heterozygote phenotype appears intermediate between the two parents. In the F2 generation, if the three gene pairs segregate independently, the genotypic ratio will be 1 CRCR:2 CRCW:1 CW CW, and the phenotypic ratio will be 1:2:1 for red:pink:white.

When the F1 generation is self-crossed to produce F2 progeny, we must calculate the phenotypic ratio for each trait separately due to independent assortment. For flower color, we expect a 1:2:1 phenotypic ratio (red:pink:white), whereas for the other traits, we observe a traditional 3:1 Mendelian ratio for dominant to recessive phenotypes because these traits follow complete dominance. The proportion of F2 plants that will resemble the F1 phenotype can be calculated by multiplying the probabilities of each individual trait expression.

User Antoan Milkov
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2 votes

Answer:

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

Step-by-step 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

User Nojo
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