Chapter 7 - Beyond Alleles Flashcards
What is a polygenic trait?
A trait influenced by many genetic loci, such as interaction between alleles or interaction with the environment.
Discrete genes can cause continuous variation through…
genes at many loci environment.
Genetic + environmental influences =
Continuous distribution!
How do we measure variation?
Variance, which measures the dispersion within a population. Genetic variance is the raw material for selection.
What are the components for phenotypic variation?
Vp (total phenotypic variance) = Vg (variance due to genetics) + Ve (Variance due to environmental differences)
What are the components of variance?
They are quantitative traits controlled by many loci. We study this to understand how traits evolve through a simplified model.
Who were the mutationists?
When G.M’s law of inheritance was rediscovered in 1900, people were impressed by the power of single mutations.
Who were the biometricians?
The opposite of mutationists, they were impressed by the continuous variation in traits they saw within populations. They rejected Mendalian genetics, believing that discrete genes cannot explain continuous variation we see in natural selection.
Who was Thomas Hunt Morgan?
He wanted to show that, as a saltationist, he could create a new species in the lab via mutation. However, rather than proving this, he noticed that mutations increased variance rather than producing a new species.
How was conflict resolved between Mendelians and biometricians?
They were reconciled via models in pop genetics. Ronald Fisher combined the theory of many small discrete genes creating continuous variation and gave birth to Quantitative genetics.
Natural selection changes _ in a population, resulting in _.
allele frequencies, evolution.
How do we know that evolution of continuous traits via natural selection fits with particulate inheritance of individual mutations?
Fisher, Haldane, and Wright proved it.
Who was Sewell Wright?
He was the co-founder of population egenetics, and invented inbreeding co-efficient and the idea of an adaptive landscape.
What was the “Modern Synthesis”?
An effort to combine field studies, paleontology, pop. genetics into a coherent whole.
What is Kimura’s Neutral Theory?
The idea that substitutions at a neutral loci occur at a steady rate that can be used as a molecular clock.
The rate of subs is expected to be constant in big and small populations, so evolution is a constant thing across lineages.
He finally concluded that evolution at many loci must be occuring under genetic drift, not selection.
