Mendel's first law, also known as the Law of Segregation, states that during the formation of gametes, the alleles for a trait separate so that offspring acquire one factor from each parent. In a monohybrid cross, which involves one trait with two alleles, this leads to a typical phenotypic ratio in the offspring. The alleles combine in pairs to give three possible combinations: two homozygous (one dominant, one recessive) and one heterozygous. The dominant trait will express itself when present.
For a monohybrid cross involving a homozygous dominant and a homozygous recessive parent, symbolized as (AA x aa), the F1 generation is all heterozygous (Aa) and displays the dominant phenotype. When these F1 heterozygotes are crossed (Aa x Aa), the resulting F2 offspring will have the genotypes: AA, Aa, and aa.
AA and Aa: Show the dominant phenotype.
aa: Shows the recessive phenotype.
Counting these occurrences, you get:
AA = 1
Aa = 2
aa = 1
Therefore, the phenotypic ratio is 3 dominant : 1 recessive.
Thus, according to Mendel's first law, the monohybrid phenotypic ratio is 3 : 1.
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According to Mendel's first law, also known as the Law of Segregation, the monohybrid phenotypic ratio is 3 : 1.
This law states that during the formation of gametes, the two alleles for a trait separate, so each gamete carries only one allele.
When two heterozygous parents (with genotype Aa) are crossed, the offspring genotypes follow the ratio 1 AA : 2 Aa : 1 aa.
Phenotypically, since the dominant allele masks the recessive one, three offspring show the dominant trait while one shows the recessive trait.
Thus, the observable trait ratio, or phenotypic ratio, is 3 dominant : 1 recessive.
Mendel discovered this pattern through his experiments on pea plants, studying traits like flower color and seed shape.
This fundamental principle of genetics helps explain inheritance patterns and is the foundation of classical genetics.
Understanding the 3:1 ratio is essential for predicting offspring traits and studying heredity.
Therefore, Mendel's first law describes how traits segregate and combine to produce predictable phenotypic ratios in offspring.
