TERMS FOR TEST 3 Flashcards
adaptation
an inherited trait that makes an organism more fit in it;s abiotic (non-living) and biotic (living) environment, and that has risen as a result of the direct action of natural selection for its primary function.
antagonistic pleiotropy
A hypothosis that proposes that the genes that code for beneficial effects also codes for deleterious effects in other contexts
coevolution
When evolutionary change in one species can affect selective conditions for a second species.
differential reproductive success
One of the three conditions of natural selection. Individuals with certain traits are more successful than others at surviving and reproducing in their environment.
exaptation
A trait that serves one purpose today but evolved under different conditions and served a different condition in the past.
gene duplication
an extra copy of a working gene is formed. Once an organism has two copies of one gene, one of the gene copies might change to a new function, while the other can remain unchanged and thus perserve the original function.
gene sharing
a protein that serves one function in one part of the body is recruited to perform a new and different function in a second location.
inheritance
One of the three conditions of natural selection. Some differences in poulations are inherited by offspring from their parents.
life history strategy
the schedule and manner of investment in survivorship and reproduction of an individual in a lifetime.
marker gene
a gene used in nuclear biology to determine if a nucleic acid sequence has been successfully inserted into an organism’s DNA.
norm of reaction
Genes produce a trait that that may differ according to the context of a set of environmental conditions.
pleiotropic genes
when genes affect more than one characteristic.
trade-off
EX: :Larger offspring may survive with higher probabilities but because such offspring require more resources during thier in utero development than do smaller offspring, fewer larger offspring will be produced.
variation
One of the three conditions of natural selection. Individuals in a population differ from one another,
selection coefficient
to quantify the strength of natural selection, a parameter called the selection coefficitent is used, labeled s to describe the fitness reduction of one type.
frequency-independent selection
fitness associated with a trait is not directly dependent on the frequency of the trait in a population.
directional selection
one allele is constantly favored against the other allele. IE selection drives allele frequencies in a single direction toward an increasing frequency of the favored allele.
Fixation
when an allele becomes fixed (impossible according to the hardy-Weinberg model for an infinite population size.
Over dominance
also known as heterozygote advantage, check page 221 for more info
Frequency-dependent selection
when the costs and benefits associated with a trait depend on its frequency in the population. Can be positive or negative, positive means the fitness associated with a trait increases as the frequency of the trait increases in the populations. With negative, the fitness associated with a trait decreases as the frequency of the trait increases in the population. under negative frequency-dependent selection, each phenotype is favored when it is rare.
Fecundity
the number of offspring produced
Wright-Fisher model
a way to think about small populations in a quantitive way. Basically a small version of the Hardy-Weinberg model. Check page 246
Genetic drift
the process of random fluctuation in allele frequencies due to sampling effects of finite populations.
The Three consequences of genetic drift
In a finite population, allele frequencies fluctuate over time, even in the absence of natural selection.
Some alleles are fixed, others are lost, and th fraction of heterozygotes int he population decreases over time
Separate populations diverge in their allele frequencies and in terms of which alleles are present.
selectively neutral
no difference in fitness between alleles
observed heterozygosity
used to measure the amount of variation in a population. A fraction of the individuals in the population that are heterozygous at the given location.
expected heterozygosity
the fraction of heterosygotes expected under the Hardy Weinberg model, given the allele frequencies of the population.
population bottleneck
When populations become very small, even for a short time, allele frequencies change dramatically. The sampling that occurs during the reduction of population size and because of the accelerated pace of genetic drift in a small population.
Founder Effect
the change in allele frequencies that result from sampling effects that occur when a small number of individuals from a large population initially colonize a new area and found a new population. Genes of founders usually only represent a subset of the genes present in the mainland population and so te allele frequencies ofin the founders may deviate by chance from those in the large population. Extremely rare alleles that are extremely rare may become common.
Substitutions
when a new allele arises by mutation and is subsequently fixed in the population. The substitution rate is defined as the rate at which new 3alleles become fixed int he population.
Neutral theory
proposed that at a molecular level of DNA sequence:
1 Most of the variation present within a population is selectively neutral.
2 most of the changes in dna or amnio acid sequence over time - and thus many of the molecular differences between related species - are selectively neutral.
3 Most of the genetic variation within a population is neutral and thus not subject to natural selection.
Pseudogenes
non-functional and typically untranslated segments of DNA that arise from previously functional genes.
Particularly very informative about evolutionary history as they are derived fro, homologous genes and subject to neutral drift.
Molecular clock
The fact that substitutions occur in the population at the same rate that neutral mutations arise in an individual.
Substitution rates at different loci do not depend of population size or other demographic parameters, neutral mutations arise at similar rates in different taxa and should also be fixed at similar rates.
Nearly neutral theory
posits that most substitutions are, if not exactly neutral, only mildly deleterious. Therefor population size plays a critical role in determining the balance between drift and selection.
Heterozygosity in Genetic Drift
When an allele heads towards fixation, less alleles are available to make heterozygous pairs
Name the three different types of selection and how they work
Directional
Heading towards one homozygous pair
Stabilizing
Heading towards one heterozygous pair
Diversifying
Disruptive selection separating from heterozygous pair to separate homozygous pairs
Examples:
Longest tail length has highest fitness, directional
Average tail length has highest fitness stabilizing
CHANGES TO ENVIRONMENT
usually induces directive selection followed by stabilizing
Positive dependent selection
More rare greater the fitness
IE left or right mouthed fish example.
Negative frequency selection
More common greater the fitness
IE butterfly example
Genetic Drift
Not due to natural selection, due to sampling error. Can affect allele frequencies that are affected by natural selection. Genetic drift does not result in adaptation. Only natura selection does.
Absolute fitness equation
better fitness over worse fitness
