Q.10 Derine and Explain Mendel’s Law of Independent Assortment.
Answer:
Definition
Alleles of a gene pair segregate (get separated and distributed to gametes) independently from the alleles of other gene pair. This is called as law of independent assortment.
Dihybrid Cross
It is a cross in which two contrasting traits are studied at a time. In next crosses, Mendel studied dihybrid crosses.
Traits
Traits under study were as follows:
Seed shape
It has two distinct forms:
(a) Round
(b) Wrinkled
Seed Colour
It has also two distinct forms:
(a) Yellow
(b) Green
Dominance
The trait of round seed was dominant over wrinkled, similarly yellow seed colour was dominant over green.
Alleles controlling traits
Round seed shape is controlled by R’ and wrinkled by ‘r’, similarly yellow seed colour is controlled by ‘Y’ and green by ‘y?
P1 Generation
Mendel crossed the true breeding plant that had Round yellow seeds with true breeding wrinkled green seeds.
F1 Generation
All seeds in F1 generation were round yellow.
F2 generation
When FI seeds grow into plants they were self fertilized. This cross produced seeds with four phenotypes. There were 315 round yellow seeds, 108 round green seeds, 101 wrinkled yellow seeds. and 32 wrinkled green seeds.
Ratio in F2 Generation
The ratio of these phenotypes was 9:3:3:1
“The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after R.C. Punnett (an English mathematician). The gametes of both parents having all possible genetic set-ups are determined. A checker board is used to cross all the possible gametes of one parent with all the gametes of other parent. In this way, a biologist can find all the possible genotypes of offspring.
Conclusion
Mendel explained that two traits i.e., seed shape and seed colour are not tied with each other. The segregation of ‘R’ and ‘r’ alleles happens independently of segregation of ‘Y’ and ‘y’ alleles.
