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It is a complex trait because multiple genetic and environmental factors impact the phenotype. [13] [14] The phenotype before the threshold is referred to as normal or absent, and after the threshold as lethal or present. These traits are often examined in a medical context, because many diseases exhibit this pattern or similar. [9]
Convergent evolution—the repeated evolution of similar traits in multiple lineages which all ancestrally lack the trait—is rife in nature, as illustrated by the examples below. The ultimate cause of convergence is usually a similar evolutionary biome , as similar environments will select for similar traits in any species occupying the same ...
Directional selection for both traits during the same time period would increase the positive correlation between the traits, while selection on only one trait would decrease the positive correlation between the two traits. Eventually, traits that underwent directional selection simultaneously were linked by a single gene, resulting in pleiotropy.
Cave paintings (such as this one from France) represent a benchmark in the evolutionary history of human cognition. Victorian naturalist Charles Darwin was the first to propose the out-of-Africa hypothesis for the peopling of the world, [40] but the story of prehistoric human migration is now understood to be much more complex thanks to twenty-first-century advances in genomic sequencing.
This chart illustrates three patterns one might see when studying the influence of genes and environment on traits in individuals. Trait A shows a high sibling correlation, but little heritability (i.e. high shared environmental variance c 2; low heritability h 2). Trait B shows a high heritability since the correlation of trait rises sharply ...
Many traits are produced by the interaction of several genes. Traits controlled by two or more genes are said to be polygenic traits. Polygenic means "many genes" are necessary for the organism to develop the trait. For example, at least three genes are involved in making the reddish-brown pigment in the eyes of fruit flies. Polygenic traits ...
Heritability can be univariate – examining a single trait – or multivariate – examining the genetic and environmental associations between multiple traits at once. This allows a test of the genetic overlap between different phenotypes: for instance hair color and eye color .
Analysis on quantitative trait locus effects has been used to examine the impact of directional selection in phenotypic diversification. QTL is a region of a gene that corresponds to a specific phenotypic trait, and the measuring the statistical frequencies of the traits can be helpful in analyzing phenotypic trends. [9]