Question

Explain the law of independent assortment with a suitable example.

Answer 1

Hint: Mendel did a dihybrid cross by observing the inheritance of two genes. In a dihybrid cross plants having 2 sets of contrasting characters are chosen. Based on various dihybrid crosses, Mendel proposed a second set of generalizations in the form of the Law of Independent Assortment. It is the third law of inheritance.

Complete answer:
-According to the law of independent assortment, ”In a dihybrid cross, segregation of one pair of alleles or one pair of characters is independent of another pair of alleles or another pair of characters.”
-He took one pea plant that was having the seeds of yellow color with a round shape(YYRR). He crossed it with another pea plant with seeds having green color and wrinkled shape (yyrr).
-Their F1 progeny produced all seeds with yellow color and round shape. The gametes produced from YyRr were YR, Yr, Yr, yr respectively. They were all produced in equal proportions. This illustrates the law of independent assortment.
-As a result of selfing F2 generation produced yellow round, yellow wrinkled, green round, and green wrinkled seeds in the ratio 9:3:3:1. This is their phenotypic ratio.
-Their genotypic ratio is 1:1:2:2:4:2:2:1:1.

Additional information:
-Gregor Mendel conducted hybridization experiments on garden peas (Pisum sativum) for 7 years (1856-1863).
-Mendel selected 14 true-breeding pea lines. It has 7 pairs with contrasting characters.
-Law of dominance and the law of segregation was proposed by studying the inheritance of one gene at a time.
-However Mendel’s work remains unrecognized till 1900 due to lack of communication, mathematical approach, inability to provide physical proof, and genes being described as discrete units.

Note:
Mendelian work was discovered independently by three scientists-Hugo de Vries, Carl Correns, and Tshermak. Advancements made in microscopy helped them to observe the mechanism of cell division at various stages. This also led to the discovery of chromosomes.