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9.4. Chromosomal theory of heredity

Chromosomal theory of heredity

The Mendel 's laws were rediscovered after 1900, when he began to develop modern genetics. In 1902, Sutton, and in 1903, Boveri, posited that chromosomes were the carriers of heredity.

Since chromosomes contain hereditary elements or genes, we can assume that when they are separated in meiosis each one passes into a different cell, which would fulfill Mendel's first law.

Knowledge of chromosomes and cell reproduction (mitosis and meiosis) occurred before other scientists, such as Hugo de Vries, rediscovered Mendel's laws in the early 20th century.

The chromosomal theory of inheritance arises by relating the scientific knowledge of the cell with the experiments carried out by Mendel. Its main postulates are:

  • The genes that determine the hereditary factors of the phenotype are located on the chromosomes.
  • Each gene occupies a specific place or locus  (in the plural it is loci) within a specific chromosome.
  • Genes (or their loci) are arranged linearly along each chromosome.
  • Allele genes (or antagonistic factors) are found at the same locus of the homologous chromosome pair, so that in diploid organisms each trait is governed by a pair of allele genes.

The genetic phenomenon of inheritance corresponds to a cytological phenomenon of exchange of chromosomal segments in meiosis (recombination).

Homologous chromosomes contain identical sets of loci, and genes that occupy homologous loci are antagonistic alleles or factors.

Genes that are very close within the same chromosome tend to be inherited together (linked genes).