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Children are similar to their parents. Siblings also have many common features. In addition to the similarities, each member of the family has individual characteristics that do not appear among his relatives. When all human populations are observed, it can be seen that within some of them people are more similar to each other than in others. For example, the ethnic Swedes are very homogeneous. A population much more diverse than the Swedish population is, for example, the population of the United States of America, which was formed by the Native Americans and emigrants from all continents. This diversity of traits within the population and, more broadly, the species – is called genetic variabilitygenetic variationgenetic variability. Therefore, we will say that the variability in the population of Swedes is smaller than in the population of Americans.

There are several reasons why even closely related organisms show genetic variation, that is, they differ from each other by some features. These are:

• independent spread of chromosomes to gametes; take into account only three pairs of chromosomes; during the meiotic division, there are 4 gametes, but there are 8 possible combinations of allocation of only 3 chromosomes; in the case of people who have 23 pairs of chromosomes, theoretically every man and every woman can produce more than 8 million types of gametes;

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Ilustracja przedstawia schematycznie sposób losowego rozchodzenia się różnych chromosomów do gamet. U góry dwie gamety: ojca i matki. Każda ma po 3 chromosomy: długi, średni i krótki. U ojca oznaczone kolorem fioletowym, u matki zielonym. Z połączenia gamet postaje potomek, który ma 3 pary chromosomów. Po mejozie jego gamety mogą mieć 8 różnych zestawów chromosomów. 2 gamety maja takie same zestawy, jak rodzice. W innych chromosomy są losowo pomieszane. Na przykład długi i średni od ojca, krótki od matki. Albo długi ojca, średni i krótki matki. Na ilustracji zamieszczono napisy: Father's gamete, mother's gamete, somatic descendent cell, 3 pairs of homologous , chromosomes, gamete 1, possible, combinations of chromosomes in the offspring gametes

• genetic recombinationgene mutationgenetic recombination, taking place during the meiotic division; it is based on the fact that homologous chromosomes separeiting into the gametes, which within the pairs exchanged genetic material among themselves, so they differ from the chromosomes of the previous generation; such a process of exchanging genetic material occurs with each meiotic division;

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Ilustracja przestawia schematycznie wymianę fragmentówchromosomów w trakcie mejozy. Chromosomy w kształcie litery X, niebieski i czerwony. Para chromosomów u góry wymienia długi fragment jednego z ramion. Powstałe chromosomy są czerwono – niebieskie. Para u dołu wymienia krótki fragment na końcu jednego z ramion. Powstałe chromosomy mają tylko kropkę innego koloru w miejscu wymiany.

• random combination of gametes is an extra factor of genetic variability, causing that a couple of parents can have offspring with different genotypes;

• mutationsmutationmutations occurring in the sex cells.

Features subject to genetic variation are inherited. Due to variability, the individuals forming the species differ from each other. Because individuals have different characteristics, the chance that some of these individuals will survive the changing environmental conditions is greater than if all individuals were the same. Individuals better adapted to the new conditions give their offspring traits that allowed them to survive. Therefore, despite the death of individual individuals, the species still exists.

Summary

• The source of genetic variability is the process of gamete formation, random merging with each other and mutations.

Keywords

genetic variation, random joining of gametes, chromosomes

Glossary