Question

Define the following: (a) polygenic, (b) additive alleles, (c) monozygotic and dizygotic twins, (d) heritability, and (e) QTL.

Short answer

Question: Define the following terms related to genetics: (a) polygenic, (b) additive alleles, (c) monozygotic and dizygotic twins, (d) heritability, and (e) QTL (Quantitative Trait Loci).

Step-by-step solution

(a) Polygenic

Polygenic refers to a trait or characteristic that is determined by the interaction of multiple genes, each of which individually contributes to the expression of the trait. These multiple genes together influence the trait, rather than being controlled by a single gene.

(b) Additive Alleles

Additive alleles are the different forms (variants) of a gene that have a cumulative or additive effect on a quantitative trait. The effect of each allele adds up, contributing to the overall phenotype of an individual. This is in contrast to non-additive effects, such as dominance or epistasis, where the influence of one allele may overshadow or interact with another allele's effect.

(c) Monozygotic and Dizygotic Twins

Monozygotic twins are identical twins that develop from a single fertilized egg (zygote) that splits into two embryos. These twins have nearly identical genetic makeup, as they share the same genes inherited from their parents. Dizygotic twins, also known as fraternal twins, develop from two separate fertilized eggs (zygotes) and have different genetic constitutions. These twins share only about 50% of their genes, just like regular siblings.

(d) Heritability

Heritability is a measure of the proportion of variation or differences in a particular trait among individuals within a population that can be attributed to genetic factors. It is expressed as a value between 0 and 1, where 0 indicates that none of the variation is due to genetics, and 1 denotes that all variation is due to genetic factors. It is important to note that heritability estimates apply to populations and not to individual organisms.

(e) QTL (Quantitative Trait Loci)

Quantitative Trait Loci (QTL) are specific regions of DNA where genetic variations are associated with the expression of a quantitative trait, such as height, weight, or blood pressure. QTLs may encompass multiple genes that contribute to the trait's variation. The mapping and identification of QTLs help in understanding the genetic basis of complex traits and diseases, which are influenced by multiple genes and environmental factors.