The genotype is the genetic character of a cell, organism or an individual and it is referenced with certain characteristics being considered. The genotype of an organism is usually the inherited instructions that it carries within its genetic code. Genetic variation in populations can be analyzed and quantified by the frequency of alleles [same genes or same genetic locus]. Population genetics is determined by two great and imperative calculations and these are the genotype frequencies and allele frequencies. Genotype frequency in a population is the number of individuals with a given genotype that is divided by the total number of individuals in the population.
Genotype frequency is the proportion of the genotypes in a population. Although the allele and genotype proportions relate, there are differences to hold in your fingertips especially if conducting research on genetic variation in populations. Genotype frequency has also been effective and it guarantees a bright future when it comes to genomic profiling and making it easy to predict someone is having a disease or a birth disorder. Testing of different gene variants for prediction of diseases such as Type 2 diabetes or coronary heart disease will become easier. More so, genotype frequency can also aid in determining ethnic diversity.
Genotyping is the process of revealing the genotype an individual with a biological assay. The techniques involved include Polymerase chain reaction [PCR], DNA fragment analysis, allele specific oligonucleotide , DNA sequencing, nucleic acid hybridization and DNA microarrays or beads. DNA fragment analysis is a technique that can be used to ascertain certain disease causing genetic abnormalities such as microsatellite instability [MSI], aneuploidy, or loss of heterozygosity [LOH].
When determining genotype or allele frequency, keep in mind that the sum is always less than or equal to one [it is less than or equal to 100%]. The Hardy-Weinberg principle or law is useful in describing the relationship between genotype frequencies and allele frequencies especially when a population is not evolving. There are several factors that are known to affect genotype frequency and they include;
- Selective sexual selection- There are certain genotypes and phenotypes that get choose by mates. The alleles of the chosen mates increase in frequency while the alleles that are not chosen will decrease.
- Differential migration- Here if a certain phenotype moves out of an area, the frequency of those alleles will decrease while those that stay in a chosen area will increase.
- Assortative mating- This is a kind of mating that affects genotype frequencies expected under the Hardy-Weinberg equilibrium. This is because when an individual mate favorably with other individuals that are phenotypically similar, this leads to an overabundance of homozygous individuals occurs since similar phenotypes are likely to share akin genotypes. When mating of similar phenotypes takes place more frequently than random mating, the possibility of offspring receiving two copies of an identical allele increase perturbing the Hardy-Weinberg outlooks.
- Natural selection- certain phenotypes survive and those alleles increase in frequency whereas the alleles of the unsuccessful ones decrease.
- Isolation [Founder effect] – This is a form of genetic drift that affects genotype frequency. Here, if a small group of individuals is separated from main group, they may have a different frequency of alleles in the gene group. As population grows, these frequencies may differ from the main group.
Genotype frequencies and gene frequency are related variables and thus affected by similar factors. Besides the aforementioned factors affecting genotype frequencies, mutation and random genetic drift are the other notable factors. Genotype frequencies are easy to measure and the simplest case is working on a case where you have one genetic locus with two alleles and three genotypes. To learn more on representations of the genotype frequencies, the De Finetti diagram can aid as it is useful in population genetics presentations.
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