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Mendel's laws

German: Mendelsche Regeln

1 Definition

Mendel's laws describe how the inheritance of characteristics occurs and how its expression is determined by genes. These laws were originally determined by the observation and statistical analysis of Gregor Mendel on pea seeds. Also, the human blood types underlie these laws.

2 Mendel's laws

2.1 Law of uniformity

When you cross individuals of one species that differ homozygously in one feature in which they are homozygous, the descendants are all the same regarding this feature (same genotype). Homozygous means that there is only one allele for the gene.

2.2 Law of splitting

When you cross individual within generation F1, the features of the P- and generation F1 appear in a ratio of 3:1 or 1:2:1. Generation F1 is heterozygous for the gene; there are two types of gametes.

2.3 Law of independence

Alleles of different genes can be inherited independent from each other. When crossing the heterozygous F1 individuals, new combinations of features arise that have not been observed neither in generation P- nor in generation F1.

3 Background

Within the cells of the body, the chromosome appear in pairs. So, a human being has 23 pairs of chromosomes, or 46 individual chromosomes. This is called a diploid set of chromosomes. One set of chromosomes stems from the father, the other one from the mother. Thus, in one cell of the body, the genes for one feature are duplicated. The benefit of recombination consists in the fact that more different combinations of genes can occur. Due to sexual reproduction, there is a high variety of descendants and -therewith - of chances of survival. Additionally, errors or weaknesses of the genes are irregularly distributed among the descendants, so that a compensation for the errors is created when copying the genetic information.

4 Usage

Mendel's laws are applied:

  • in animal breeding
  • in plant cultivation, eg. in the cultivation of hybrids
  • for paternity tests, eg. for proving that certain individuals cannot be considered as parents of a child


Specialties: Genetics

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