Question

How can the random distribution of alleles result in a predictable ratio

Answer 1

Answer:

Let's recall Mendel's law of independent assortment that states, "During the formation of gametes, alleles of genes assort independently into each gamete"

How can the random distribution of alleles result in a predictable ratio?

For example, We have a trait for flower color either yellow or white, and the alleles for the flower color are Y and y. The yellow flower color is a dominant trait, and be expressed if plant has YY or Yy genotype. We cross a plant with genotype Yy with another plant Yy.

P1                                                   Yy   x  Yy

F1                                               YY : Yy: Yy: yy

Phenotype                        Yellow: yellow: yellow: white

Genotypic ratio                 1           :               2       :                 1

Phenotypic ratio                               3         :          1          

So, we see that phenotypic ratio is different from genotypic ratio. Although the distribution of alleles is random but still there are only four possible outcomes for a trait. Hence, we can predict the phenotypic and genotypic ratio of offspring by drawing a punnet square or gamete formation.