Changes in Population Genetics and other Mechanisms in Evolution Flashcards
Ways in which populations change, thus violation HW assumptions:
Bottlenecks
(One of the most frequent causes of HW assumption)
Where a gene pool is significantly reduced for some reason and a relatively small allele diversity remains
Ex. A population has the following alleles in it at one locus: A,a, B, b, C, c, D, d, E, e. If something happens that eliminates dome of the alleles at that locus (fire destroys the part of the pop. with those alleles, the members w 1 or 2 specific alleles migrate away, etc.) the population is left with a smaller diversity of alleles in the gene pool. This lower allele diversity may make a population more subject to environmental stressors.
Cheetah Bottleneck Example
- It is thought that cheetahs have gone through 2 bottlenecks in their history.
- These bottlenecks caused them to have non-random mating and small population sizes.
- As a result, their populations are experiencing severe genetic problems and are declining significantly.
Genetic Drift
- The constant changing of allele frequencies in a population over time, due to random mating.
1. Genetic Drift is random
2. Any change in allele frequency is due to chance.
3. Allele frequencies are constantly drifting up and down over time.
4. Allele changes are not adaptive
5. Drift is most infuential in small populations
6. Drift can lead to the fixation or loss of alleles
7. Genetic drift does not increase allele frequency distribution in a population. (Drift cannot increase the diversity of alleles in a population, it only changes the relative abundance of existing alleles within a population)
Random Mating Effects on Gene Frequency
Random mating changes how frequently an allele is found in a population. For example, a pop consisting of allele A at .6 and allele a at .4 in which many of the aa individuals do not mate will have the A allele at a higher frequency. in the next generation, by chance some of the individuals die off, and now there is A allele at a higher frequency in the population’s gene pool.
Gene Flow
* The movement of individuals and their alleles from one population to another
* Typically results in equilibrating allele frequencies between populations. (Flow makes the populations look more alike genetically)
* Gene flow into a pop is one of two ways in which allele frequency distribution increases.
* May cause a decline in allele diversity in the pop that the individuals are emigrating from.
the other way to increase allele diversity is mutation
Non-random mating
random mate selection is not the norm in insects, vertebrates, + others
includes assortative mating, Inbreeding, and Sexual Selection
even in organisms that broadcast gametes, population mixing is not entirely homogenous
-ex. grasses are pollinated by wind carrying pollen from plant to plant, a particular plant is more likely to be pollinated by a plant nearby
this is not random with respect to the entire interbreeding population
Assortative Mating
includes assortative and disassortative mating
Assortative Mating- An individual is more likely to mate with another that is similar in phenotype to itself
Disassortative Mating- An individual is more likely to mate with another that has a different phenotype from itself
examples: people, plants, blister beetles, wolves
Inbreeding
-The mating of individuals that share a recent common ancestor- recent is relative to the organism in question and the intent to introduce novel alleles into the offspring, or maintain allele frequency distributions the way they are.
ex: Cheetahs are almost identical genetically to the point that almost any mating between two of them might be considered inbreeding (even if the two mates and their ancestral lines have been separated for many generations). But an ancestral line of pea plants may be able to inbreed parent to offspring for multiple generations without seeing much of an effect.
Inbreeding Depression
-The loss of fitness as homozygosity in resulting offspring, future generations, as the population increases and heterozygosity decreases.
-Evolution does not occur here since allele frequency does not change (only the genotypes change).
Sexual Selection
seen in pea-fowl and guppies
seen in female choice and male-male competition
- A special case of natural selection that favors individuals with traits that increase their ability to obtain mates.
Acts on males more because femals are typically the higher investment sex. Since females invest so much in their offspring, they are choosy w their mates. Males invest little and should be willing to mate with any female. So, females of many species look less showy/large.
Female Choice
females will often choose mates with good alleles, but how?
- Males that have a healthybody can afford to have bright feathers/beaks, long tails, colorful bodies, etc.
- Those that are not healthy spend their energy in body maintenance instead.
- So, females choose mates that look a certain way… but they may choose mates on other criteria like a willingness to provide resources, care for young, defend territories, etc.
Male-Male Competition
-Sometimes males compete for mates.
-Typically the biggest and strongest are the ones that get the mates
-This may be interpreted as females choosing those mates, however, the traits that are being selected for are sorted out by the males (NOT FEMALES)
