Population polymorphisms and their causes

• A Population where the gene frequency of the most common allele is less than or equal to 0.99 (99%) is polymorphic for a given trait .
• Of course, this stated value is not an objective limit, but was only determined by agreement.
• It is most convenient to determine the degree of polymorphism using heterozygosity, which is defined as:

$H=1-\sum _{i=1}^{m}x_{i}^{2}$

where m = number of alleles of the monitored gene and x_i = gene frequency of the ith allele (C-H-W applies: x₁+x₂...+x_m=1)

or verbally as the representation of individuals in a population who are heterozygous for a particular locus.

• Example: In the population, the allele representation is p=0.5 and q=0.5.

$H=1-\sum _{i=1}^{m}x_{i}^{2}=1-0,5^{2}-0,5^{2}=1-0,25-0,25=0,5$

This is also the maximum that can be achieved. It is true that the larger m and the more unevenly distributed frequency x, the smaller H is.

The minimum would be for p → 1 and q → 0 (H ≈ 0), where the vast majority of homozygotes would be.

• Heterozygosity can therefore serve us as a good measure between subpopulations of one population.

Stable polymorphism

• gene frequencies do not change;
• e.g. population in C-H-W equilibrium, or polymorphism maintained by the frequency of heterozygotes, or mutations and back mutations.

Transitive polymorphism

• In a population, when due to selection one allele is gradually replaced by another, as is the case, for example, with selection against homozygotes.

Links

Related Articles

• Castle-Hardy-Weinberg Equilibrium
• Nucleic acid polymorphisms
• Selection
• Population

Source

• ŠTEFÁNEK, Jiří. Medicína, nemoci, studium na 1. LF UK [online]. [cit. 11/02/2010]. <https://www.stefajir.cz/>.