Genetics and Evolution

In species that reproduce sexually, the behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation…

Mutations are base for all genetic diversity but meiosis and fertilization mix it well. Meiosis through random orientation of homologous chromosomes pairs in meiosis I metaphase gives a huge assortment number (2²³ in Humans). This number is in fact greater due to crossing-overs (chromatids exchange between homologous chromosomes) during meiosis prophase I.

Random fertilization between two of so many male and female gametes increases again genetic possibilities.

Those genes pools are selected randomly through genetic drift and also natural selection if an allele gives an advantage or disadvantage to its carrier.

Mutations and mixing due to meiosis and fertilization are not sufficient to explain the biodiversity around us. Life diversification can be achieved by other means, which involve genome alteration… or not!

Some genes are not inherited from the parents. They result from a transfer of a distinct species gene, even a pretty far species. Those horizontal transfers are originally accidents and often linked with viruses but they can bring a new phenotype to the species that receives new DNA.

In plants, hybridizations between species are frequent. Most of the time, the individuals that result from those hybridizations are sterile (chromosomes from the two parents aren’t homologous and cannot pair up so meiosis can’t be achieved). However, abnormalities in cell division may happen and double the number of chromosomes. That phenomenon, known as polyploidization, leads to a possible meiosis with a twice-higher number of chromosomes and brings new fertile polyploid species.

In vertebrates, emergence of new behavior may happen without genome alteration. This new behavior can then be learnt by other members of the group mimicking the first individual to do so. Afterwards this behavior shall be taught throughout generations.