CHAPTER 20 REVIEW STUDYGUIDE
20.1- Genetic variation and evolution
∙ Darwin proposed natural selection as a mechanism for evolution ∙ Natural Selection- produces evolutionary change when individuals in a population possess certain inherited characteristics and produce more viable offspring than individuals lacking such characteristics
o Result of natural selection- populations evolve and become better adapted to their environments
o Natural selection leads to a change in allele frequencies because it favors individuals with certain alleles
∙ Lamarck formed the idea of inheritance of acquired characteristics, and said that changes that organisms experienced during their lives was passed on to their offspring
o Proven wrong by Darwin, who proved that variation was not created by experiences (like giraffes’ necks being long to reach trees), but it is instead the result of preexisting genetic differences among individuals.
Key point for Darwins theory- natural selection or genetically based variation leads to evolutionary change
∙ Changes in allele frequencies can be due to:
o Natural selection
o Mutations occurring repeatedly
o Migration and genetic drift
o Gene flow
o Nonrandom mating
∙ Genetic variation in a population is necessary for evolution to occur because natural selection occurs when some individuals are better suited for their environment than others. This means that these individuals will live longer and pass these traits on. Thus, genetic variation provides the means necessary for natural selection to act upon, thereby leading to evolution
If you want to learn more check out What is the role of the celestial sphere on the earth axis?
∙ Allele frequencies will not change and evolution will NOT occur if: o No mutation takes places
o No migration or emigration happens- leading to no genetic drift o Mating is random, which mates are not chosen based on their genes o Population size is large
o There is no natural selection
20.3- five agents of evolutionary change
∙ Mutation is the ultimate source of genetic variation and is what makes evolution possible
∙ Natural selection has no effect on mutation
∙ Very rare
2. Gene flow
∙ Occurs when alleles move between populations Don't forget about the age old question of What is the meaning of institutions in competing theories?
∙ A powerful agent of change
∙ Is successful if an individual newly arrives to a preexisting population with different allele frequencies than the organisms that are already there and mates successfully
o Allele frequency of the original receiving population may be altered over time
∙ Pollen carried by insects and seeds that blow in the wind are other examples
3. Nonrandom mating
∙ self fertilization
∙ allele frequency is not altered. Thus, it results in a decreased allele variability and diversity
∙ shifts allele frequencies
4. Genetic Drift We also discuss several other topics like Which isolation is the prevention of interbreeding due to differences in physiology?
∙ alters allele frequencies in small populations
∙ are statistical accidents. Allele frequencies my change by chance alone ∙ random fluctuation of allele frequencies increases as population size decreases
∙ bottlenose effect
o can happen after a catastrophe
o gametes of only a small number of individuals form the next generation, the alleles they exhibit are different than the
parents. Thus, the next generation is comprised of only a few individuals, which decreases genetic diversity
o EX: the northern elephant seal was hunted nearly to extinction. At some point, only 1 population remained with about 20 seals. At this point, genetic variation is lost. They are now protected and their numbers have climbed, but genetic variation will only be recovered if mutations arise
∙ genetic drift leads to the loss of alleles in isolated populations and is included as a bottlenose effect
A. Founder Effect
∙ when one or a few individuals disperse and become the founders of a new, isolated population that is a distance away from the populations origin
∙ some alleles may be lost from the new population, and others may change drastically in allele frequency Don't forget about the age old question of How do you convert prefixes?
B. Bottlenose effect
∙ Populations may go through some event that causes their populations to be greatly reduced in size
∙ If there are few surviving individuals, there will be a random genetic sample of the original population, which results in a loss of genetic diversity
∙ With natural selection, environmental conditions determine which individuals produce the most successful offspring
∙ Variation must exist
∙ Variation must result in differences in the number of offspring surviving in the next generation
∙ Variation must have a genetic basis
CHAPTER 22 REVIEW STUDYGUIDE
22.1 Biological species concept and the nature of species
∙ The biological species concept focuses on the ability to exchange genes ∙ Defines a species as groups of actually or potentially interbreeding natural populations that are reproductively isolated from other groups
∙ Says a species is composed populations whose members can mate with each other successfully IF they came in contact.
∙ Populations that do not mate with each other and don’t produce viable offspring are reproductively isolated and are thus considered to be separate species If you want to learn more check out When did we begin to see the emergence of written philosophies of child rearing in europe?
Don't forget about the age old question of What is the most profitable level of output for a monopolist?
∙ Some species that are separate population can interbreed successfully, but they don’t do so under natural conditions
∙ Reproductive isolating mechanisms (PREZYGOTIC)
o Ecological isolation- species are in the same area, but occupy different habitats and rarely encounter each other long enough to mate
o Behavioral isolation- different species have different mating rituals o Temporal isolation- species reproduce in different seasons or at different times of the day
o Mechanical isolation- structural differences between reproductive organs prevents successful mating
Lock and key
o Prevention of gamete fusion- sperm cant reach the egg properly or the egg of one species is toxic to the sperm of a different species
∙ Reproductive isolating mechanisms (POSTZYGOTIC)
o Hybrid inviability- breeding of two species that are similar that results in a sterile, hybrid offspring
o Post zygotic reproductive isolating mechanisms prevent the normal development into reproducing adults
22.3- the role of genetic drift and natural selection in speciation
∙ Populations may diverge for completely random reasons.
o EX: Genetic drift in small populations, founder effects, and population bottlenecks may lead to changes in allele frequency and genetic diversity that cause reproductive isolation
∙ Any two isolated populations can experience genetic drift over a period of time, even large populations. This may affect traits that are responsible for reproductive isolation and cause speciation
∙ Adaptation can lead to speciation.
o EX: one population of flies adapts to wet habitats and another adapts to dry habitats, natural selection will occur for the differences in traits. These differences can cause ecological and behavioral isolation ∙ Selection can also act directly on mating behavior