Mendel’s Laws

The basic rules of heredity were first described by Gregor Mendel as a result of his study on pea. He postulated existing of material factors that determine traits. He also assumed (basing on results of experiments) that every organism has two of such factors. They correspond with alleles. Every diploid organism has two alleles laying on homologous chromosomes.

The analysis of his results enabled observing some regularities. Mendel’s law tells us that:

• one randomly chosen allele goes to a gamete
• traits are inherited independently

The first one is true in every case. During meiosis haploid cells originate. Half of them have one of the alleles, half of them the other one, so the chance for an allele to be in a certain gamete is 0.5 (it’s random)

The second law is true only for genes from different chromosomes or the ones that lie far enough on one chromosome that frequency of crossing-over causes nearly independently inheriting. Chromosomes go to gametes as a whole, all the genes on one chromosome are inherited together.