Migration, genetic drift and non-random mating are factors which can cause changes in the allele and genotype frequencies present in a population. These changes are seen over generations and result in evolution.
Migration can be represented as either immigration or emigration. Immigration is defined as the movement of individuals into a country which is not their location of origin. Conversely emigration is classified as moving from one country with the desire to settle in another. Basically, emigration and immigration mean the same thing, but immigration is used when considering movement from the country of origin. Migration can cause new genetic variation to enter into a population and these can alter allele and genotype frequencies over subsequent generations.
Random mating is possible when all individuals within a population have an equal chance of mating with any other individual of the same species. However, non-random mating often occurs and thus, not all individuals have the same probability of mating. Non-random mating may take place because of active mate choice or inbreeding. Inbreeding tends to occur especially in endangered animal populations where the mating pool is small. Active mate choice can be either assortative or disassortative.
1. Assortative mating takes place when individuals with the same or similar phenotypes mate with each other more frequently than would be probable under random mating.
2. Disassortative mating is when there is higher than likely mating between less similar individuals than would be thought under random mating.
Genetic drift is a random event which causes changes in the allele frequencies in a population as a result of sampling error. The effects of genetic drift are stronger in smaller populations because certain genes can reach fixation at a faster rate. This can in turn lead to a decrease in genetic diversity.
Migration, genetic drift and non-random mating are three different factors which can all cause changes in the allele frequencies present in a population. Over time certain alleles will reach fixation faster than others as a result of natural selection.
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