Laws of Inheritance



Gregor Mendel (1822-1884) was not only an Augustinian monk, but also a founder of genetics and a teacher of high school students. Although his main field was natural science, he became famous because of his sweet peas research.

The results of Mendel´s research were summarized in the monograph - Experiments with Plant Hybrids. At the beginning was the foundation of an atypical variant of flower, which Mendel planted with the typical one. Their offspring get traits from both of the parents and this was the first step on the genetic way. It took him more than seven years of his life and thousands of experiments in mice, plants and sweet peas, before he finally discovered the law of inheritance.

1) The Law of Segregation
Each of the parents transmits only half of its hereditary factors to offspring. The possible combinations of gametes depends on the number of paternal alleles. E.g. if a parent has two pairs of alleles (dominant – A,B and recessive – a,b), there are four combinations transfer to children (AB,Ab,aB,ab). An offspring receives always just one member of allelic pairs (A or a, B or b).

2) The Law of Independent Assortment
Alleles make up a gene and most of the genes can be assorted independently. Nowadays we know, that the last sentence was true at the time of Mendel, but later was discovered the exception - genetic linkage.

3) The Law of Dominance
Genes work in different variants - called alleles - which can be dominant or recessive and just the dominant ones are expressed in a phenotype. Recessive traits occur only, when no dominant allele is present.

Mendel´s Research
Gregor Mendel followed 7 signs in sweet-peas (Pisum sativum):



Exceptions to Mendel´s Rules

 * 1) Genetic linkage
 * 2) Penetrance
 * 3) Codominant alleles, specific alelic interactions
 * 4) Epigenetics
 * 5) Gonosomal inheritance
 * 6) Extrachromosomal (e.g. mitochondrial) inheritance





Related articles

 * Allele
 * Gene
 * Phenotype
 * Genetic Linkage
 * Genetic Linkage Analysis
 * Extrachromosomal and Non-Mendelian Inheritance