Evolutionary Processes Flashcards
The 5 Hardy-Weinberg assumptions
Allele frequencies in a population will remain constant assuming:
1. no mutations
2. no gene flow
3. random mating
4. no genetic drift
5. no selection
Is the Hardy-Weinberg realistic?
No the 5 required conditions are rarely (if ever) met. Changes in the frequency of genes are likely.
Deviation from the Hardy-Weinberg equilibrium
Deviations from the Hardy-Weinberg equilibrium (where all 5 assumptions are met) indicate that evolution has taken place.
Microevolution
A change in gene frequency (what traits are common) in one population over time
Genetic Mutation
A cause of microevolution. It is the raw material for evolutionary change (changes DNA) and provides a new combination of alleles
Gene Flow
A cause of microevolution. Movement of alleles between populations. (Seeds are carried into a new population area, or individuals migrate in/out of a population)
A lot of gene flow reduces the differences between different populations.
Nonrandom Mating
A cause of microevolution. When individuals do not choose mates randomly but through assortative mating and sexual selection
Assortative mating
individuals select mates with a similar phenotype and reject those who are different from them.
Sexual Selection
Males compete for the right to reproduce and females choose the male with the best phenotype. (female peacocks choose males with the most colorful tails)
Genetic Drift
A cause of microevolution. Occurs by a random event that causes a disproportionate sampling of genes to be selected. Causes gene pools to become dissimilar from each other, and some alleles are completely lost while some become fixed (unopposed).
Likely to occur after a bottleneck, inbreeding, or when founders start a new population.
Bottleneck effect
A random event prevents a majority of individuals from entering the next generation. (A forest fire takes out half a forest, the next generation is composed of alleles that just happened to survive).
Founder effect
When a new population is started from just a few individuals. The alleles carried by population founders are dictated by chance.
Formerly rare alleles will either occur at a high frequency or not at all.
(The Amish community has many cases of dwarfism and polydactilism, because the founders happened to have those traits).
Natural Selection
Adaptation of a population to the biotic (living) and abiotic (non-living) environment.
The ONLY reason for adaptation, and a major cause of microevolution
4 requires for natural selection
- Variation
- Inheritance
- Differential Adaptiveness
4.Differential Reproduction
Variation
The members of a population differ from one another
Inheritance
Many differences between individuals are heritable genetic differences
Differential Adaptiveness
Some differences in traits affect survivability
Differential Reproduction
Some differences affect likelihood of successful reproduction
Natural Selection results in…
A change in allele frequencies and improved fitness of the population
Polygenic traits
Most traits are polygenic (are made up of many alleles) and therefor result in a normal bell-shaped curve
3 types of selection
Directional, Stabilizing, and Disruptive Selection
Directional Selection
The curve shifts left or right.
If there was a sudden height growth in the population, the bell curve would move to show the new normal (now taller) height
Stabilizing Selection
The peak of the curve increases and tails decrease.
When human babies with low or high birth weights are less likely to survive, you will get many more babies at the average.
Disruptive
The curve splits into two different peaks.
Oysters are either white or black, because both colors equally blend in with the environment. However, middle tones such as grey or brown stick out.
Where is genetic drift the most impactful?
In small populations
