Question

A pure breed tall pea plant with green pod and pure breed dwarf pea plant with yellow pod is given to you .Explain gamet formation by law of independent assortment and with punnet square explain phenotypic and genotypic ratio

Answer 1

Principles of Inheritance

Mendel conducted experiments on Pisum sativum, the garden peas from 1857 to 1865. The results of which, he published under the title ‘Experiments In Plant Hybridization’ and presented before Brunn society for the sturdy of natural sciences in 1865.
Mendel chose his monastery garden and considered seven out of thirty different traits of pea plants for his experimental studies.  There were several reasons for Mendel to have chosen pea plants over others. They were,

Easily available and easy to growShort life span of one yearBisexual flowersNaturally self-pollinatingAvailability of contrasting set of characters



Mendel choose 7 different traits of pea plant for his experiments. Given below is the table which includes those traits.



Pure lines – Pure breeding lines are the organisms which give birth to same kind of organisms, generation after generation. So, all pure breeding tall plants only produced tall plants and dwarf only produced dwarf plants.
The cross is represented using the phenotype,which is the external appearance of the organism, and genotype which is the genetic composition of the trait in consideration.
Each trait, has an alternative version of its gene that is located at a specific location, on a specific chromosome and is called allele.  For example, the trait height, has two alleles T, the gene for tallness and t, the gene for dwarfness. Here, the dominant gene is represented in capital letter and the recessive in small letter.
The pure breeding tall plant will have the genotype TT, is called homozygousfor that trait. When a pair of genes in a plant are identical like [TT] or [tt],  the plant is considered to be homozygous for that gene pair.
When a pair of contrasting genes are present in plant for a trait like [Tt], it is considered as heterozygous for that gene pair. Such a plant is called hybrid as two parents who are genetically different gave rise to an heterozygous individual.
Dominant gene is the gene which expresses itself in the heterozygous or hybrid condition, i.e. in a condition of Tt, the gene T expresses itself, masking the effect of the gene t. Thus, the plant which is heterozygous for height with genes Tt, will be tall due to effect of gene T. So, T is the dominant gene and hence is represented in capital letter.
Gene for dwarfness, t is called recessive as it remains hidden or unexpressed in presence of dominant gene T. To understand better, consider the cross between pure breeding tall and pure breeding dwarf.


hope you understand