Mendel’s laws are fundamental laws of heredity (genetics). Heredity is the transmission of traits and characteristics from parents to subsequent generations. The Augustinian priest, teacher and geneticist Johann Gregor Mendel (1822 – 1884) was the first researcher to methodically investigate the rules of heredity and is known as the “founder of heredity”. He was unaware of the existence of genes and chromosomes. He conducted his experiments on peas and beans. Three laws resulted from his crossing experiments, which were published in 1865 under the title: “Experiments on Plant Hybrids”.
Uniformity Law
If one crosses two individuals of a species that differ in a characteristic for which they are homozygous, the offspring in the first daughter generation (F1- generation) are the same among themselves (uniform) with respect to this characteristic.
Example: The eye color brown (B) is dominant to the eye color blue (b). If one parent is homozygous for the eye color brown (BB) and the other parent is homozygous for the eye color blue (bb), you have in the F1- generation only offspring with brown eyes. However, they are heterozygous (Bb) for the trait eye color brown.
Cleavage Law
If you cross the individuals of the F1- generation among themselves, then the individuals of the F2- generation are no longer equal, but split according to certain numerical ratios. In dominant-recessive inheritance, one obtains a ratio dominant to recessive of 3:1.
Example: Both parents are heterozygous for the eye color brown (Bb). With four children in the F2 generation, three have brown eyes and one has blue eyes. One child is homozygous for the eye color brown, two are heterozygous. The child with blue eyes is homozygous for the eye color trait.
Independence Law
If one crosses individuals of the same species that differ in several traits in a homozygous manner, the law of uniformity and the law of cleavage apply to each trait. In addition to the trait combinations of the parents, new trait combinations appear in the F2- generation.
Small Encyclopedia of Genetics
- Dominant: (lat. ruling); characteristic-determining.
- DNA: deoxyribonucleic acid, storage form of genetic material.
- Gene: hereditary factor, hereditary plant
- Heterozygous: heterozygous
- Homozygous: homozygous
- Recessive: (lat. go back); inferior to the dominant gene.
