Law
of independent Assortments (Second Law)
This law states that
when two pairs of traits are combined in a hybrid, segregation of one pair of
character is independent of the other pair of characters at the time of gamete
formation.
It also gets randomly
rearranged in the offspring producing both parental ad new combinations of the
characters. The law was proposed by Mendel, based on the results of dihybrid
crosses, where inheritance of two traits were considered simultaneously.
Mendel performed
di-hybrid cross in pea plants that were true breeding for two traits, for
example, a plant that had round seeds and yellow seed color was cross pollinated
with a plant that had wrinkled seed and green seed color.
In this cross, the
traits for round seed (RR) and yellow seed color (YY) are dominant. Wrinkled seed
(rr) and green seed color (yy) are recessive. The resulting offspring F1
generation were all heterozygous for round seed and yellow color (RrYy). This
means the dominant traits of round seed shaped and yellow color completely
masked the recessive traits in F1 generation.
Mendel allowed the F1
plants to self-pollinate, thus in F2 generation he noticed a ratio of (9:3:3:1)
in phenotypes this has been explained in Fig.3.2.
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