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bio 225 chp 4
| Question | Answer |
|---|---|
| how is natural selection and sexual selection different? | natural selection stresses the aspect of surviving to reproduce, while sexual selection stresses access to mates. (evolution only sees phenotype). |
| what are the conditions for natural selection to occur? | 1. more offspring born than can survive 2. individuals vary within a species 3. some of that variation is inherited 4. differences in fitness are due to some of that variation |
| what did Charles Darwin and his cousin Francis Galton first do? | they were the first ones to use the term survival of the fittest, and was referring to a population and survival was a continuation of population. Fitness refers to the organisms in relation to their environment. |
| what's absolute fitness? | absolute fitness (W) is the number of offspring produced over a lifetime and is calculated with W = Ps x F. Ps is the probability of survival and F is fecundity. the problem is that variation in fitness among individuals isn't accounted for. |
| what's fitness components? | fitness components is the elements of an organism's life cycle and sees how each stage affects their fitness. in animals it would include survivorship from zygote to maturity, the ability to find mates, fecundity, and fertilization success. |
| what's relative fitness? | relative fitness is the fitness of different states divided by a standard, the different states are different genotypes. |
| what's adaptation? | adaptations are states of a trait that increase the average fitness of a population. They increase survival probabilities or reproductive success or both compared to other character states. |
| what's a selection coefficient? | 1-W and measures the strength of selection. closer to 0 means little selection, close to 1 means those genotypes don't survive or reproduce. |
| what can natural selection drive? | it can drive allele frequencies to fixation. when allele frequencies are fixed there's only one allele in the population so genetic variation has been lost, but natural selection can also preserve genetic variation. |
| what is underdominance and overdominance? | underdominance is when there is a codominant relationship among alleles and the heterozygote has the disadvantage (lower fitness). overdominance leads to equilibrium of p=0.5 and preserves genetic diversity, heterozygote advantage (higher fitness). |
| what's density dependent selection? | the selection coefficient is not constant, but varies based on allele frequency. there is an inverse relationship between the selection coefficient and density resulting in strong selection against the allele when common and weaker selection. |
| what is pleiotropy and linkage? | pleiotropy is multiple traits from one gene, linkage is when one loci are on the same chromosome. the closer the genes are together the more likely they will be inherited together. loci that are closer together are less likely to crossover during meiosis1 |
| what's a polygenic trait? | polygenetic traits are determined by multiple genes, examples of polygenic traits in humans include height and skin color. many polygenic traits are continuous. |
| what's stabilizing selection? | selection against the extremes and the mean phenotype has the highest fitness. |
| what's directional selection? | when a phenotype other than the mean has the highest fitness. one extreme has a higher fitness. the mean phenotype will shift. |
| what's balancing selection? | when all genotypes have equal fitness (heterozygous advantage). no natural selection. |
| what's disruptive selection? | when phenotypes that are away from the mean have the highest fitness (not always extremes). |
| what's wrong with perfection? | perfection is not an idea and not quantifiable. since 95% of all species that ever lived are now extinct, it shows that natural selection can't lead to perfection, but instead extinction. |
| what are evolutionary trade offs? | the constraints on a trait by the conditions on another trait. ex: a tree can't grow faster without growing weaker. a common trade off is between reproduction and survivorship. |
| what's an evolutionary stable strategy? | a combination of trade offs that have higher fitness than alternatives. one can have fewer but larger offspring or many smaller offspring. each of these can be stable but also may not be.more offspring are required to offset lower survivorship. |
| what's heritability and genetic penetrance? | the consistency of the expression of the genotype. complete penetrance is when different genotypes are consistently represented by the some phenotypes natural selection can only be effective when the connection between them are consistent. |
Created by:
sarsar