Principles of Inheritance And Variation – Notes

First and Second Laws of Inheritance
Gregor Johann Mendel carried out several hybridization experiments with true-breeding pea lines which had sharply contrasting characters.
A monohybrid cross is the study of inheritance of one pair of contrasting characters.
The Law of Dominance states that in a monohybrid, pure line cross between parents with contrasting traits, the dominant from appears in the F1 generation and both forms appear in a ratio of 3:1 in the F2 generation.
The Law of Segregation states that alleles do not show any blending but segregate from each other during gamete formation into different gametes.
Punnett Square is a graphical representation that helps calculate the probability of all possible genotypes of the progeny in a genetic cross.
A test cross is a cross between individuals if the F1 generation and a homozygous recessive parent to determine the genotype of an individual.

Chromosomal Disorders
Chromosomal disorders are caused due to changes in chromosomal number or chromosomal structure.Changes in chromosomal number occur due to non-disjunction of chromosomes or failure of chromatids to disjoin during cell-division.