"One of the earliest scientists to make big strides in recognizing and understanding DNA variability was Gregor Mendel (1822–1884), an Austrian monk whose work inspired early twentieth-century studies in genetics.
He observed certain flower and seed trait variations in the offspring of peas and other garden plants following his controlled matings.
In some cases, a progressive continuum of flower color could be noticed in the offspring. In other cases, the traits segregated in seemingly predictable statistical outcomes. We now know these to be simple or qualitative traits controlled by a single gene—a very rare occurrence in nature.
These qualitative traits in pea plant flower color were due to a
changed pigmentation-related gene that produced white flowers (no pigment) rather than pigmented purple flowers.
These qualitative traits in pea plant flower color were due to a
Because pea plants, like most animals, have two sets of chromosomes (one from the mother and the other from the father), even if a pea plant had only one good copy of a pigmentation gene, it could still produce purple flowers. If a plant had two copies of the altered gene, white flowers would result.
The key thing about Mendel’s work was that it demonstrated that genes or other chromosomal features could be shuffled around via matings in a population to create a diverse amount of variability. We also now know that nearly all traits in creatures, especially those that facilitate adaptation, are actually controlled by many genes and regulatory elements located across the genome at specific sites called loci (singular, locus). Genetic
differences between loci variants are called alleles.
The potential for trait variability can be quite large due to the many possible allele combinations contributing to a trait. These types of traits are called polygenic (controlled by many genes) or quantitative traits (as compared to qualitative). These polygenic loci or alleles are typically referred to as quantitative trait loci (QTL) and are all interconnected in complex gene regulatory networks. Each locus contributes to different levels of variability in the trait being studied.
Quantitative traits and QTLs can be characterized in two different ways. The original approach was to perform controlled matings of a plant or animal to create a large population of offspring. Each individual was then characterized for visible traits (phenotypes) and had its genome mapped with DNA markers. Traits associated with a specific set of alleles (marker-connected loci) are determined by statistically analyzing the percent variability they contribute to a certain trait.
As genome sequencing became more common and efficient, this mapping strategy was largely replaced and/or supplemented by sequencing the entire genome of a large sample (cohort) of individuals from a population.
The key thing about Mendel’s work was that it demonstrated that genes or other chromosomal features could be shuffled around via matings in a population to create a diverse amount of variability. We also now know that nearly all traits in creatures, especially those that facilitate adaptation, are actually controlled by many genes and regulatory elements located across the genome at specific sites called loci (singular, locus). Genetic
The potential for trait variability can be quite large due to the many possible allele combinations contributing to a trait. These types of traits are called polygenic (controlled by many genes) or quantitative traits (as compared to qualitative). These polygenic loci or alleles are typically referred to as quantitative trait loci (QTL) and are all interconnected in complex gene regulatory networks. Each locus contributes to different levels of variability in the trait being studied.
Quantitative traits and QTLs can be characterized in two different ways. The original approach was to perform controlled matings of a plant or animal to create a large population of offspring. Each individual was then characterized for visible traits (phenotypes) and had its genome mapped with DNA markers. Traits associated with a specific set of alleles (marker-connected loci) are determined by statistically analyzing the percent variability they contribute to a certain trait.
As genome sequencing became more common and efficient, this mapping strategy was largely replaced and/or supplemented by sequencing the entire genome of a large sample (cohort) of individuals from a population.
Traits of interest are then correlated with variations in genome sequence in what are called genome-wide association studies.
In fact, it is now possible to do this with populations from multiple environments. The outcome of such studies reveals both the location and DNA sequence of alleles connected to a variety of traits in organisms inhabiting different environments."
ICR