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Chapter 8: Problem 18

Mendelian ratios are modified in crosses involving autotetraploids. Assume that one plant expresses the dominant trait green seeds and is homozygous (WWWW). This plant is crossed to one with white seeds that is also homozygous \((w w w w) .\) If only one dominant allele is sufficient to produce green seeds, predict the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) results of such a cross. Assume that synapsis between chromosome pairs is random during meiosis.

Short Answer

Expert verified
Answer: The predicted F2 generation phenotypic ratio is 7:1 for green seeds to white seeds.

Step by step solution

01

Determine parental genotypes and phenotypes

The parental plants have the following genotypes and phenotypes: - Parent 1: Genotype - WWWW, Phenotype - Green seeds - Parent 2: Genotype - wwww, Phenotype - White seeds
02

Determine possible gametes from parental genotypes

In the parental generation, each plant produces the following gametes: - Parent 1 (WWWW): Gametes - WW, WW, WW, WW - Parent 2 (wwww): Gametes - ww, ww, ww, ww
03

Predict F1 generation genotypes and phenotypes

The F1 generation is produced by the cross between the gametes of Parent 1 and Parent 2: - F1 Genotype: (WW)(ww) or WWWW As only one dominant allele is sufficient to produce green seeds, all individuals in the F1 generation will have green seeds.
04

Determine possible gametes from F1 genotypes

In the F1 generation, a plant has the genotype WWWW. There are different possibilities for the formation of gametes due to random synapsis during meiosis: - Gametes: Ww, Ww, Ww, Ww
05

Predict F2 generation genotypes and phenotypes

The F2 generation is produced by the cross between the gametes of the F1 individuals (self-fertilization): - F2 Genotypes: * 1/8 WWWW * 4/8 WwWW * 1/8 (ww)(WW) or WWww * 2/8 (Ww)(Ww) or WwWw The F2 Phenotypes: - Green seeds (having at least one dominant W allele): 7/8 - White seeds (having all four recessive w alleles): 1/8 The predicted F2 generation phenotypic ratio is 7:1 for green seeds to white seeds.

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