{"id":9574,"date":"2026-06-01T21:33:48","date_gmt":"2026-06-01T21:33:48","guid":{"rendered":"https:\/\/kapdec.com\/help\/?p=9574"},"modified":"2026-06-01T21:33:48","modified_gmt":"2026-06-01T21:33:48","slug":"population-genetics","status":"publish","type":"post","link":"https:\/\/kapdec.com\/help\/population-genetics\/","title":{"rendered":"Population Genetics"},"content":{"rendered":"<h2><strong>Unit : Natural selection<\/strong><\/h2>\n<h3><strong>Chapter: Population genetics<\/strong><\/h3>\n<p><strong><em>Reference:<\/em><\/strong> <em>Population genetics, Gene frequency, Genotype frequency, Hardy-Weinberg principle, Factors leading to frequency change, Mutations, Recombination of genes, Genetic drift, Founder effect, Bottleneck effect, Gene migration (gene flow), Natural selection, Importance of population genetics<\/em><\/p>\n<p><strong><em>&nbsp;<\/em>Learning objectives<\/strong><\/p>\n<ul>\n<li>To understand the evolutionary factors responsible for showing variations in a population<\/li>\n<\/ul>\n<p><a name=\"_Hlk133595359\"><strong>Population genetics<\/strong><\/a> is the study of genetic variation within and among populations and the evolutionary factors that explain this variation.<\/p>\n<p><a name=\"_Hlk133595378\"><strong>Gene frequency<\/strong><\/a> can be defined as the fraction or percentage of a population that carries allele (i.e., one type of a gene variant) at a particular locus. It is also more appropriately known as allele frequency.<\/p>\n<p><strong>Genotype frequency<\/strong> in a population is the number of individuals with a given genotype divided by the total number of individuals in the population. In population genetics, the genotype frequency is the frequency or proportion (i.e., 0 &lt; f &lt; 1) of genotypes in a population.<\/p>\n<p><strong>Hardy-Weinberg principle<\/strong><\/p>\n<ul>\n<li>Coined by G. H. Hardy and W. Weinberg, which describes the genetic structure of evolving population.<\/li>\n<li>Mutations introduce new genes into species resulting a change in gene frequencies.<\/li>\n<li>Gene frequency is defined as the frequency with which a particular allele occurs in the population.<\/li>\n<\/ul>\n<p>According to Hardy-Weinberg principle allele frequencies in a population are stable and is constant from generation to generation i.e., the gene pool remains constant, called genetic equilibrium.<\/p>\n<p>According to this principle a population is only at equilibrium when there is-<\/p>\n<ul>\n<li>No mutation<\/li>\n<li>No natural or artificial selection<\/li>\n<li>No gene flow (no gene migration)<\/li>\n<li>No genetic drift<\/li>\n<li>No genetic recombination<\/li>\n<\/ul>\n<p>Individual frequency for may be named as P, q. etc. in a diploid organism p and q represent the frequency of allele A and a. the frequency of AA individuals in a population is p<sup>2<\/sup>. This can be stated in another way, i.e., the probability that an allele A with a frequency of p appears on both the chromosome of a diploid individual is the product of the probabilities i.e., p<sup>2<\/sup>. Similarly, of aa is q<sup>2<\/sup>, of Aa is 2 pq. Thus, is a binomial expansion of (p+q)<sup>2<\/sup>. It is possible to calculate all allele and genotype frequencies using the expressions allele frequency p+q = 1 and genotype frequency p<sup>2<\/sup>+2pq+q<sup>2<\/sup>=1<\/p>\n<p><strong>Factors leading to frequency change<\/strong>:<\/p>\n<p>When the frequency of alleles changes in a population, it means the population has evolved.<\/p>\n<p>Genetic equilibrium and population heterogeneity are influenced by five factors. These elements are referred to as evolutionary agents.<\/p>\n<p>These are the following: mutations, genetic recombination, gene flow or gene migration, genetic drift, natural selection.<\/p>\n<p><strong>Mutations:<\/strong><\/p>\n<ul>\n<li>These are massive, rapid alterations in the genetic material that are passed down down the generations.<\/li>\n<li>Mutations are random.<\/li>\n<li>Many mutations are either harmful or harmless.<\/li>\n<li>The rate of mutation is quite low.<\/li>\n<li>Mutations add new genes and alleles to a gene pool, as well as generating and maintaining population variations.<\/li>\n<li>The accumulation of mutations over a lengthy period can lead to speciation.<\/li>\n<\/ul>\n<p><strong>Recombination of genes:<\/strong><\/p>\n<ul>\n<li>Sexually reproducing organisms and those with gametogenesis followed by fertilisation have more opportunities for recombination.<\/li>\n<li>Even though only existing characters are reshuffled and no new genes are produced, recombination causes redistribution of distinguishing traits across individuals in a population.<\/li>\n<li>In many organisms, different combinations result in genetic and phenotypic variation. As a result, recombination acts as an evolutionary catalyst.<\/li>\n<\/ul>\n<p><strong>Genetic drift:<\/strong><\/p>\n<p>It is the occurrence of chance variations in the frequency of alleles, resulting in a random change in allele frequency. Two forms of genetic drift are the founder effect and the bottleneck effect.<\/p>\n<p><strong>1. Founder effect<\/strong><\/p>\n<p>When a small group of individuals breaks away from a larger population and creates its own population in a separate location, rare alleles could be overrepresented in this newly &quot;founded&quot; population. If this new population is isolated and interbreeds, then the resulting population could have a high frequency of certain traits.<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Example:<\/strong> The Afrikaner (Dutch) population that settled in South Africa had an abnormally high count of Huntington&#39;s Disease, because the first Dutch settlers had a high frequency of the gene (compared to the original Dutch population).<\/p>\n<p><strong>2. Bottleneck effect<\/strong><\/p>\n<p>The bottleneck effect occurs when a random event, such as a natural disaster, unselectively reduces the size of a population. The resulting population is much less genetically diverse than the original population. Some alleles may become eliminated and some may become overrepresented.<\/p>\n<p><strong>Example:<\/strong> After the northern elephant seal almost went extinct as a result of extensive hunting, the seal was placed under government protection. Since then, the population has grown, but all the descendants have little genetic variation since so few elephant seals remained.<\/p>\n<p><strong>Gene migration (gene flow):<\/strong><\/p>\n<ul>\n<li>A modest quantity of immigration can result in substantial changes in allele frequencies if two populations are genetically quite dissimilar.<\/li>\n<li>If migrating individuals contact with members of the local population, a process known as hybridization, many novel alleles may be introduced into the host population&#39;s gene pool.<\/li>\n<li>This is known as gene migration, and gene flow refers to the addition or removal of alleles as people arrive or leave a group from another location.<\/li>\n<li>When gene flow is allowed, the differences across gene pools are reduced, and the distinctiveness of populations is reduced.<\/li>\n<\/ul>\n<p><strong>Natural selection:<\/strong><\/p>\n<p>Natural selection is the process through which nature favours substantially more fitted individuals from a heterogeneous population over the less adapted individuals.<\/p>\n<p><strong>Importance of population genetics<\/strong><\/p>\n<ul>\n<li>Population genetics seeks to understand how and why the frequencies of alleles and genotypes change over time within and between populations.<\/li>\n<li>It is the branch of biology that provides the deepest and clearest understanding of how evolutionary change occurs.<\/li>\n<\/ul>\n<p><strong>Solved examples<\/strong><\/p>\n<p><strong>Example 1<\/strong>.A gene pool consists of&#8212;&#8211;<\/p>\n<p>a) all the alleles selected by natural selection<\/p>\n<p>b) all the alleles present in a population<\/p>\n<p>c) the entire genome of a sexually reproducing organism<\/p>\n<p>d) the frequencies of the alleles for a gene locus within a population<\/p>\n<p><strong>Solution 1:<\/strong> b. A gene pool consists of all the alleles present in a population<\/p>\n<p><strong>Example 2<\/strong>. <a name=\"_Hlk133595314\">The effect that is produced when an insect carries pollen grains from one population to another is called<\/a><\/p>\n<p>a) gene flow b) random mating c) mutation d) genetic drift<\/p>\n<p><strong>Solution 2:<\/strong> a. The effect that is produced when an insect carries pollen grains from one population to another is called gene flow.<\/p>\n<p><strong>Summary<\/strong><\/p>\n<ul>\n<li>Population genetics is the study of genetic variation within and among populations and the evolutionary factors that explain this variation.<\/li>\n<li>Gene frequency can be defined as the fraction or percentage of a population that carries allele at a particular locus.<\/li>\n<li>Genotype frequency in a population is the number of individuals with a given genotype divided by the total number of individuals in the population.<\/li>\n<li>Genetic equilibrium and population heterogeneity are influenced by five factors.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Unit : Natural selection Chapter: Population genetics Reference: Population genetics, Gene frequency, Genotype frequency, Hardy-Weinberg principle, Factors leading to frequency change, Mutations, Recombination of genes, Genetic drift, Founder effect, Bottleneck effect, Gene migration (gene flow), Natural selection, Importance of population genetics &nbsp;Learning objectives To understand the evolutionary factors responsible for showing variations in a population [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[629],"tags":[],"class_list":["post-9574","post","type-post","status-publish","format-standard","hentry","category-ap-biology"],"_links":{"self":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/posts\/9574","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/comments?post=9574"}],"version-history":[{"count":0,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/posts\/9574\/revisions"}],"wp:attachment":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/media?parent=9574"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/categories?post=9574"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/tags?post=9574"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}