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Chromosomal Theory of Inheritance

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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 Mendelā€™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 ā€“ 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.

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