Chromosomal Theory of Inheritance

 

Chromosomal Theory of Inheritance

• The chromosomal theory of inheritance was proposed independently by Walter Sutton and Theodore Boveri in 1902.

• They stated that behavior of chromosomes was parallel to behavior of genes and used chromosome movement to explain Mendel’s laws.

• The hereditary factors are carried in the nucleus.

• Like the Mendelian alleles, chromosomes are also found in pairs.

• The sperm and eggs having haploid sets of chromosomes fuse to re-establish the diploid state.

• Morgan extensively worked on fruit flies, Drosophila melanogaster and provided experimental evidence to support the chromosomal theory of inheritance.

Comparison between the behavior of Genes and Chromosomes

Genes	Chromosomes
Occurs in Pairs.	Occurs in Pairs.
Segregate at the time of gamete formation such that only one of each pair is transmitted to a gamete.	Segregate at gamete formation and only one of each pair is transmitted to a gamete.
It has independent pairs segregate independently of each other.	It has only pairs segregates independently of another pair.

Linkage and Recombination

T.H. Morgan carried out several dihybrid crosses in Drosophila to study the genes that are sex – linked. He observed that when the two genes in a dihybrid cross are located on the same chromosome, the proportion of parental gene combinations in the progeny was much higher than the non-parental or recombination of genes.

• Physical association of genes located on a chromosome is known as linkage.

• In a dihybrid cross, if the two genes are tightly linked or present on the same chromosome, the parental combination is more prevalent than non-parental combinations or recombinants.

• The linkage and recombination are directly dependent on the distance between a pair of genes. More the distance, greater is the probability of recombination.