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Genetic diversity (intra‑species) is the diversification of alleles of genes in pools of genespool of genespools of genes of the population of a given species.

High genetic diversity makes it possible for species to create various adjustments (adaptationsadaptationadaptations), for example to fight with predators and pathogens (viruses, pathogenic microorganisms, parasites).

There is a continuous evolutionary arms race in nature between the hosts and parasites, and between predators and preys, which is a sign of coevolutioncoevolutioncoevolution. By shuffling within pool of genes and appearing of new mutations in genotypes the adaptations appear which enable specific species to achieve superiority over the enemy species, which is reflected in their better adaptation to living conditions in changing environmental conditions.

„Individuals which are more immune produce more offspring and at least some of the individuals from the offspring inherit genes determining increased immunity. As a consequence, the appearance of mutated genes in a given population is more frequent. Analogically, when it comes to pathogens, new mutations increase the efficacy of infecting the hosts, e.g. by breaking their natural defence mechanisms. Pathogens which acquired the ability to infect the host more efficiently multiply more intensively, and therefore they spread in the host’s population more effectively.

The direct cause of decrease in genetic diversity is the decrease in number of individuals in a population. Genes are transferred from one generation to another randomly. The bigger number of individuals has specific allele, the more probable it is that it will be passed onto next generation and it will be strengthened in a population. However, if a specific allele appears in a population occasionally, there is high probability that it will disappear from the pool of genes. Therefore, only properly high population number guarantees passing diversified genetic material onto the next generations. High number of individuals also mean more chances for the appearance of mutations and obtaining new alleles of genes of adaptational importance.

An important cause of the decrease in genetic diversity is extinction of local subspecies or varieties of wild organisms, as well as the appearance of more and more selected, genetically homogeneous varieties of crop plants and breeds of farm animals. With the extinction of wild varieties, all unique alleles, which were in their genotypes and determined the adaptation to local environmental conditions, disappear.

One of the method of preserving a feature desired by a human is inbreedinginbreedinginbreeding, which means crossbreeding of closely related organisms, resulting in the increase in homozygosity in offspring. Individual offspring are very similar to each other in terms of genes, and in the case of crop plants they are sometimes clones. In this way, the pool of genes is depleted gradually in next generations. The use of inbreeding in plants contributes to increase in yields, but it also leads to a situation when new varieties are more susceptible to the attack of various pathogens. In animals, it may lead to increased meatiness of pigs or milkness of cows, but it also reduces the immunity of these animals to diseases.

Thanks to selective breeding people obtained many varieties and breeds of plants and animals. There are thousands of varieties especially for ornamental plants, e.g. roses, which were crossed and selected due to numerous desired characteristics: size of flowers, their colour, scent, ability to climb on supports, production of many thorns or lack of thorns, tree or miniature type, winter hardiness. Due to that they maintained many alleles of genes. Similarly to roses, the species of domestic dog, represented by many breeds, still maintains high genetic diversity.

Summary

• Genetic diversity enables the adaptation of a species to environmental changes.

• Mutations, by enriching the pool of genes of a population, may give the organisms the advantage reflected by their better accommodation to living conditions in changing environmental conditions.

Homework

Task 2.1

1. Estimate the probability (high – low) that all the people in the world will die because of an epidemic of a new disease. Justify your prediction.

Task 2.2

2. Kakapo is a species of a big, flightless parrot (the heaviest parrot in the world) at risk of extinction. As far back as in the mid‑19th century it inhabited almost half of the area of New Zealand. Currently its territory range is limited to few small islands, and its genetic diversity is poor. Explain what was the probable reason for the impoverishment of pool of genes of this species.

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Ilustracja przedstawia rysunek zielonego ptaka kakapo oraz mapy Nowej Zelandii, określające obszar występowania kakapo do roku 1840 i obecnie. Ptak, przypominający zieloną papużkę nielotkę stoi na ziemi, z korzonkami roślin w dziobie i w pazurach. Pierwsza mapa przedstawia występowanie kakapo na początku dziewiętnastego wieku, kiedy terytorium ptaka rozciągało się prawie na połowie obszaru Nowej Zelandii. Druga mapa ilustruje aktualny zasięg gatunku, ograniczony raptem do kilku małych wysepek Nowej Zelandii.

Keywords

Pool of genes, adaptation, inbreeding, coevolution

Glossary