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Zorluk: ZorMendel's First Law and Monohybrid Inheritance

In a monohybrid cross between two heterozygous green-pod pea plants (GgGg), Mendel's Law of Segregation predicts that 75%75\% of the F2F_2 offspring will possess the heterozygous (GgGg) genotype.

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False
The statement is false because a monohybrid cross of two heterozygous individuals (Gg×GgGg \times Gg) yields a genotypic ratio of 1 GG:2 Gg:1 gg1\ GG : 2\ Gg : 1\ gg. Exactly 50%50\% (22 out of 44) of the F2F_2 offspring inherit the heterozygous genotype (GgGg). The claimed 75%75\% proportion applies to the dominant phenotype, improperly interchanging genotypic composition with phenotypic expression.

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1
Identify parental genotypes and apply Mendel's First Law
Both parents are heterozygous (Gg×GgGg \times Gg). During gamete formation, alleles segregate so each gamete receives either GG or gg with equal probability (50%50\%).
Mendel's Law of Segregation states that allele pairs separate during gametogenesis.
2
Determine expected offspring genotypic proportions
Random combination of gametes yields 1/4 GG1/4\ GG, 2/4 Gg2/4\ Gg, and 1/4 gg1/4\ gg. The genotypic ratio is 1:2:11 : 2 : 1.
A standard Punnett square for a monohybrid cross combines GG and gg alleles from both parents.
3
Evaluate the statement's genotypic percentage claim
The heterozygous (GgGg) fraction is 2/42/4, which equals 50%50\%. The 75%75\% value corresponds to the dominant phenotype (GG+Gg=25%+50%=75%GG + Gg = 25\% + 50\% = 75\%).
The statement incorrectly equates the dominant phenotypic percentage (75%75\%) with the heterozygous genotypic percentage (50%50\%).

Anahtar Kavram

Mendel's Law of Segregation and Monohybrid Genotypic vs Phenotypic Ratios
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Mendel's First Law and Monohybrid Inheritance

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