Principles of Inheritance and Variation

Principles of Inheritance and Variation PDF Notes, Important Questions and Synopsis

SYNOPSIS

Heredity is the transmission of characters from one generation to another through direct genetic descendants.
Mendel’s Laws of Inheritance:

Punnett square is a graphical representation to calculate the probability of all possible genotypes of offspring in a genetic cross.
Test cross is a cross between the F₁ hybrid and its recessive parent. It confirms the purity of the F₁ hybrid, whether it is homozygous or heterozygous.
Back cross is a cross between the F₁ hybrid and one of its parents, which may be dominant or recessive.
Incomplete dominance occurs when two parents are intercrossed with each other, and the hybrid produced does not resemble either of its parents but is mid-way between the parents.
Multiple allelism occurs when more than two alleles exist at a given locus of a chromosome. In a given individual, only two of these alleles occur, one derived from each parent.
Co-dominance is the phenomenon when both alleles of a pair are fully expressed in a heterozygote, so the genes and traits are said to be co-dominant.
Linkage is the tendency of the genes to remain together during the process of inheritance.
Differences between complete linkage and incomplete linkage:
Crossing over is the mutual exchange of segments of non-sister chromatids of homologous chromosomes during the process of meiosis.
Chromosomal Theory of Inheritance was proposed by Walter Sutton and Theodor Boveri. Sutton combined the knowledge of chromosomal segregation with Mendelian principles and called it the chromosomal theory of inheritance.
Sex Determination in Humans:
Mutation is an abrupt and discontinuous process where a gene or a chromosome undergoes heritable change in its structure or number.
Ways of Chromosomal Mutation:
Mendelian disorders are determined by alteration or mutation in a single gene.
Aneuploidy is a condition where an organism possesses fewer or extra chromosomes than the normal genome number of the species; e.g. (2N – 1) or (2N + 1), where N is the haploid chromosome number.
Chromosomal disorders are caused by the absence or excess or abnormal arrangement of one or more chromosomes.