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Zorluk: OrtaMendel's First Law and Monohybrid Inheritance

In pea plants (*Pisum sativum*), the allele for green pod color (GG) is completely dominant over the allele for yellow pod color (gg). Which expected offspring phenotypic ratio corresponds to each parental cross?

  • GG×ggGG \times gg100% Green pods
  • Gg×GgGg \times Gg3 Green : 1 Yellow pods
  • Gg×ggGg \times gg1 Green : 1 Yellow pods
  • gg×gggg \times gg100% Yellow pods

Cevap

Crossing homozygous dominant with homozygous recessive (GG×ggGG \times gg) yields 100% green pods; crossing two heterozygotes (Gg×GgGg \times Gg) produces a 3 green to 1 yellow phenotypic ratio; crossing a heterozygote with a homozygous recessive (Gg×ggGg \times gg) results in a 1 green to 1 yellow phenotypic ratio; and crossing two homozygous recessives (gg×gggg \times gg) yields 100% yellow pods.
According to Mendel's Law of Segregation, parental alleles segregate during gamete formation and combine at fertilization. A homozygous dominant crossed with homozygous recessive (GG×ggGG \times gg) produces only green offspring (GgGg). A monohybrid cross between two heterozygotes (Gg×GgGg \times Gg) produces 3 green (1GG+2Gg1 GG + 2 Gg) to 1 yellow (1gg1 gg). A testcross of a heterozygote (Gg×ggGg \times gg) produces a 1:1 ratio of green to yellow. Crossing two recessive parents (gg×gggg \times gg) results exclusively in yellow offspring.

Adım Adım Çözüm

1
Determine allele interaction and parent gametes for GG×ggGG \times gg.
The GGGG parent contributes only GG gametes, and the gggg parent contributes only gg gametes. All offspring have genotype GgGg.
Mendel's Law of Segregation states that allele pairs separate during gamete formation.
2
Determine phenotypes for GG×ggGG \times gg.
Since GG (green) is dominant to gg (yellow), all GgGg offspring are green (100% Green pods).
Heterozygotes express the dominant trait.
3
Construct Punnett square for Gg×GgGg \times Gg.
Genotypes: 1GG,2Gg,1gg1 GG, 2 Gg, 1 gg. Phenotypes: GGGG and GgGg are green, gggg is yellow.
Combining 1GG+2Gg=31 GG + 2 Gg = 3 green vs 1gg=11 gg = 1 yellow gives a 3:1 phenotypic ratio.
4
Analyze testcross Gg×ggGg \times gg.
Genotypes: 50%Gg50\% Gg and 50%gg50\% gg. Phenotypes: 1 Green : 1 Yellow.
The heterozygous parent contributes GG and gg in equal proportions (1:1).
5
Evaluate gg×gggg \times gg.
All offspring are gggg (100% Yellow pods).
No dominant GG allele is present in either parent.

Anahtar Kavram

Mendel's First Law and Monohybrid Cross Phenotypic Ratios
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Konular

Mendel's First Law and Monohybrid Inheritance

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