QQuestion
With the help of an example explain how the phenotypic and genotypic ratios found in F2 generation of certain hybrid crosses indicate exception to Mendel’s first law of heredity.
✓Answer
In the case of incomplete dominance, such as flower colour in Mirabilis jalapa (Four o’clock plant), the F2 generation shows a phenotypic ratio of 1 red : 2 pink : 1 white flowers instead of the usual 3:1 ratio. The genotypic ratio matches the phenotypic ratio because the heterozygote (pink flowers) has an intermediate phenotype. This indicates that the first law (Law of Segregation) has exceptions where alleles do not show complete dominance.
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