Linkage and Recombination
The term linkage and crossing over is introduced by TH Morgan. The physical association of parental genes in a chromosome is called linkage, such genes are called Linked genes and recombination is used to describe non-parental gene combinations. When two genes in a dihybrid cross were situated on the same chromosome, the proportions of parental gene combinations were much higher than in the non-parental type. Linked genes are exceptions to the law of independent assortment (3rd law).
Later Morgan’s student Alfred Sturtevant used the frequency of recombination between genes on the same chromosome as a measure of distance between genes and mapped their position on chromosomes. Genetic maps are used in human genome projects (HGP).
Principles of Inheritance and Variation CBSE Notes for Chapter 4
Inheritance is the term given to the process by which characters are passed from parents to offspring which forms the basis of heredity. Heredity is the process of passing down genetic traits from parents to offspring. The degree of difference in characters between a parent and offspring is called variation. All these are studied under genetics which deals with the study of inheritance and variation of characters passed from parents to offspring. The first proper documented study of this inheritance and variation was done by G.J. Mendel which is why he is considered the father of genetics.
In a living cell, the chromosomes of a particular gene are present in a diploid manner and each one is called an allele. Genotype is the genetic make-up of an organism i.e. the TT or tt. Whereas phenotype is the external morphological appearance or expression of the genotype i.e. TT phenotype will be tall and for tt phenotype will be dwarf.
Table of Content
- Mendel’s Laws of Inheritance
- Inheritance of One Gene
- Inheritance of Two Genes
- Chromosomal Theory of Inheritance
- Linkage and Recombination
- Pleiotropy and Polygenic Inheritance
- Sex Determination
- Mutation
- Pedigree Analysis
- Genetic Disorders
- CBSE Previous Year Question Papers
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