Week 4 Flashcards
What are the 2 sources of genetic variation?
Mutations & recombination
species
individuals that can exchange genetic material through interbreeding
gene pool
all the alleles present in all individuals in the species
populations
interbreeding groups of organisms of the same species living in the same geographical area
what are the types of mutations discussed?
- Somatic
- Germ-line
- Neutral
- Deleterious
- Advantageous
Somatic mutation
occurring in the body’s tissues
germ-line mutation
occurring in the reproductive cells and therefore passed on to the next generation
deleterious mutation
harmful effect on the organism, usually in the protein-coding regions, not always eliminated from the gene pool of a species
advantageous mutation
improve the carriers’ changes of survival or reproduction, result in better adaptation
recombination
segregation of homologous chromosomes during meiosis
allele frequencies
the rates of occurrence of alleles in populations
what does it mean for allele frequencies to be fixed?
a population only exhibits one allele at a particular gene
they are fixed for that allele
measure genetic variation using genetics instead of observable traits
many traits are encoded by a large number of genes
the phenotype is a product of both the genotype and the environment
gel electrophoresis helped identify different proteins, and therefore genetic variation
3 ways to measure allele frequencies in populations
- observable traits
- gel electrophoresis
- dna sequencing
Understanding of populations/organisms/species prior to theory of natural selection
adaptations, the exquisite fit of organisms to their environment, were evidence of a God
Species were born into the world already well-adapted by God
Who is Thomas Malthus? What did he write about?
Wrote “Essay on the Principle of Population (1798)
Said natural populations have the ability to increase in size geometrically; populations get larger at an ever-increasing rate.
What did Darwin conclude?
Species are not unchanging; they have evolved over time.
Theory of Natural selection
Natural selection
results in allele frequencies changing from generation to generation according to the allele’s impact on the survival and reproduction of individuals
Rules of Natural selection
- All populations have the ability to grow exponentially
- Limited resources prevent populations from growing exponentially
- Variation exists within a population
- This variation must be heritable
Give an example of heterozygote advantage
Sickle Cell Anemia
AA = Normal blood cells; vulnerable to malaria SA = Some sickled cells, not vulnerable to malaria SS = all sickle cells, not, not vulnerable to malaria
fitness
a measure of the extent to which the individual’s genotype is represented in the next generation
direct fitness
only the genes that you pass to your offspring
indirect fitness
only the genes that you share with your non-offspring relatives
inclusive fitness
all the genes you pass to your offspring and those you share with your non-offspring relatives
modern synthesis
there could be several genes that contribute to a trait
extends Mendel’s theory to include multiple genes per trait that could account for patterns of continuous variation that we see
microevolution
change in allele or genotype frequencies in a population over one or more generations
macroevolution
microevolution over a period of time long enough to allow for substantial phenotypic change
positive selection
natural selection that increases the frequency of a favorable allele
negative selection
natural selection that decreases the frequency of a deleterious allele
balancing selection
a number of selective processes in which multiple alleles are actively maintained in the gene pool of a population
happens when the heterozygotes have a higher frequency than either homozygote
stabilizing selection
maintains the status quo and acts against extremes
the majority of natural selection is stabilizing because most mutations are deleterious and produce an extreme phenotype that is selected against
directional selection
leads to a change in a trait over time, going towards one of the extremes
artificial selection
practiced by humans, a form of directional selection, like natural selection but the competition is removed
disruptive selection
operates in favor of extremes and against intermediate forms
sexual selection
promotes traits that increase an individual’s access to reproductive opportunities, acting in the opposite direction of natural selection
intersexual selection
interactions between females and males,
peacock example:
females prefer male peacocks with larger and more beautifully colorful tails
intersexual selection
interactions between individuals of one sex, males competing with each other to have more power, better land, better fighting skills
migration
movement of individuals from one population to another
the consequence of migration is homogenizing the populations, making them more similar to each other and reducing genetic differences between them
gene flow
the movement of alleles from one population to another
genetic drift
the random change in allele frequencies from generation to generation
> acts more harshly on smaller populations because sampling from generation to generation is more variable in small populations than large
does not lead to adaptations since the alleles whose frequencies are changing as a result of genetic drift do not affect an individual’s ability to survive
if acting alone, genetic drift could still cause changes in the allele frequencies of a population
bottleneck
an originally large population falls to just a few individuals
> results in dramatic changes in allele frequencies
loss of much of the genetic variation that was present in the original population
founder event
a few individuals start a new population
> for example, when some individuals arrive on an island and colonize it
allele frequencies change and genetic variation is lost
Non-random mating
individuals select mates according to their genotype
> certain phenotypes will increase and others will decrease
inbreeding, in which mating occurs between close relatives, will increase the frequency of homozygotes and decrease the amount of heterozygotes without affecting allele frequencies
inbreeding depression
a reduction in the child’s fitness caused by homozygosity of deleterious recessive mutations
> an issue in conservation biology, when endangered species are bred in captivity with just a small number of individuals. the species will lose genetic diversity due to genetic drift
altruism
an act of self-sacrifice that helps another, apparently for the good of others
> contradicts natural selection because altruistic acts decrease fitness and therefore should be selected against
what are solutions to the altruism/natural selection contradiction?
group selection
evolutionarily stable strategy
group selection
the idea that natural selection operates on individuals is a less powerful force than another form of selection that operates on groups
> groups with altruistic individuals work better as a unit
benefitting the group is selected over benefitting the individual
evolutionarily stable strategy
a kind of behavior that cannot be readily driven to extinction by an alternate strategy
> in the case of altruism, this behavior is not an evolutionarily stable strategy because it can be readily driven to extinction by an alternative strategy (selfish behavior)
group selection in general is not a stable strategy because it can be overthrown by more selfish strategies that will increase individual fitness
reciprocal altruism
individuals exchanging favors
> one way altruism can evolve because group selection does not provide a strong explanation for the evolution of altruism
individuals must recognize each other and remember previous interactions
how does relatedness of individuals play a role in the evolution of altruism
if rB>C then altruism can evolve
B = the benefit of the behavior to a recipient r = the degree of relatedness between recipient and donor C = the cost of the behavior to the donor
kin selection
a form of natural selection that favors the spread of alleles that promote behaviors that help close relatives or kin
> a child is worth 0.5, and niece or nephew is worth 0.25, cousins are worth 0.125
in diploid-haploid systems (the women are diploid and the men are haploid), sisters are more closely related to each other than a daughter to a mother
organisms want to do what makes their genetic makeup spread as far as possible
eusocial
species with overlapping generations in a nest, cooperative care of the young, and clear and consistent division of labor between reproduces and non-reproducers
>species receive benefits from living in and defending a nest, like easily communicating with one another about the location of food or resources
EX:
queen bee = reproducer; workers = non-reproducers
Hardy-Weinberg Equilibrium
describes the situation in which evolution does not occur, the absence of evolutionary forces, allele and genotype frequencies do not change
p^2 + 2pq + q^2 = 1
p + q = 1
Hardy-Weinberg Equilibrium requirements
- there can be no difference in the survival and reproductive success of individuals
- populations must not be added to or subtracted from by migration
- there can be no mutation
- the population must be sufficiently large to prevent sampling errors
- individuals must mate at random
selection
the differential success of alleles
Biological species concept
species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups
the most widely accepted definition of a species
limited because it doesn’t account for organisms who do not exchange genetic information and reproduce asexually, such as bacteria
because it depends on reproduction, this concept also excludes species which are extinct and only known about through the fossil record, like dinosaurs
reproductive isolation
members of different species cannot produce offspring
ring species
species with populations that are reproductively but not genetically isolated, they exchange genetic material through other, linking populations
> highlights another shortcoming of the biological species concept
EX: greenish warblers
>the 2 populations on the ends cannot reproduce, but they share genetics because the genes are passed through the populations between them
>they can’t reproduce together but are still sharing genetic material
hybridization
interbreeding between different species
>usually occurs between plants, but sometimes animals
>the biological species concept should classify a willow and an oak tree as one species because they can reproduce and form a hybrid, but we know
>natural selection must work against the hybrid offspring
ecological niche
a complete description of the role the species plays in its environment – its habitat requirements, its nutritional and water needs, and the like
> another way of characterizing a species
its not possible for 2 species with very similar niches to exist in the same space because the competition will inevitably lead to the extinction of one of the species, which gave rise to the ecological species concept
ecological species concept
the idea that there is a one-to-one correspondence between a species and its niche
