d4.1 (natural selection) Flashcards
reasons for natural selection x2
Not all offspring that are produced will survive and reproduce because of a struggle for resources
Some individuals are more likely to survive and reproduce than others because of their heritable traits
what 3 levels can see variation across a species?
physical, physiological, and behavioral levels
4 ways variation within a species can occur
Mutation: is the original source of variation, with new alleles produced by changes in the DNA
Gene flow: the movement of genes between different groups of organisms
Meiosis: crossing over and independent assortment during the formation of egg and sperm which leads to the creation of new combinations of alleles
Sexual reproduction: random fertilization between egg and sperm of different parents
what type of cells see the most mutations?
highest in bacteria and viruses
rates of mutation largely depend on what?
on reproductive rate
how does processes of meiosis and fertilization cause genetic variation?
shuffles alleles from past mutations into new combinations
however there is an overall trend for more offspring to be produced than can be supported by what?
the resources available in the habitat
2 evolutionary benefits to overproduction of offspring
increases the odds that at least some of the offspring will survive to adulthood, required for continuity of the species.
ensures there is ample genetic variation in the population should the species need to adapt to changing environmental conditions
overproduction of offspring leads to the potential for what type of growth? what does it mean?
exponential growth of a population in which it increases in size each year
why can’t exponential growth of a natural population grow infinitely?
resources in the environment (such as adequate food, shelter, water, and mates) are limited
define logistic growth
in which there is rapid growth at first when the population is small and resources are plentiful, but the growth rate slows as the population size increases and resources begin to be in short supply
competition is the result of what 2 key reasons?
overproduction of offspring and limited resources
definition and example of direct competition (elk)
when one individual directly affects another’s ability to obtain resources
for example, a male elk will use aggression demonstrate dominance and to prevent other males from mating with a female
definition and example of indirect competition (grizzly)
when individuals indirectly compete for resources, such as territory, light, or prey
for example, an individual may deplete a shared resource, such as a grizzly bear catching a salmon so that the salmon can no longer be eaten by bears at different points along the river
impact of a negative selection pressures
decreases the frequency of a trait
impact of a positve selection pressures
increases the frequency of a trait
biotic selection pressures x5
predation
competition
disease
finding and attracting mates
availability of food
abiotic selection pressures x7
temperature
water availability
light availability
oxygen and carbon dioxide concentrations
natural disasters (floods, fires, storms)
pollutants
wind
abiotic selection pressures are often what? what does this mean
density independent, meaning they act the same no matter the population density
define biological fitness, what makes an individual more or less ‘fit’?
a measure of an organism’s ability to survive to reproductive age, find a mate, and produce offspring
individuals are more or less “fit” which means they are more or less likely to survive and reproduce as a result of a selective pressure and their heritable traits
how can the pace of evolutionary change in a population vary from selection pressure?
rapid evolution will occur if the selection pressure is higher
gradual evolution will occur if the selection pressure is lower
state and explain the two major forms of sexual selection as a selection pressure
intersexual selection (one biological sex chooses which individual of the other sex to mate with): females are usually choosier while selecting their partners based on structural and behavioural traits, therefore individuals with the most appealing characteristics are likelier to mate and reproduce successfully, ↑ frequency of the trait in the population over time
intrasexual selection (competition between members of the same sex for access to members of the opposite sex): can be physical combat, displaying strength, and vocalization, responsible for the evolution of secondary sexual characteristics in males (i.e. deer antlers, beetle horns, and large body sizes). individuals with the advantage when fighting off potential competitor are likelier to mate and reproduce successfully, ↑ frequency of the trait in the population over time
sexual selection can result in the development of physical and behavioural traits which do not provide what?
any survival benefits but do help to maximize an individual’s reproductive success
watch a video on models of endler’s investigation of selection in guppy fish. ensure you can answer the following questions:
what is the impact of predators on the number of spots on male guppies? use natural selection to explain the results.
what is the impact of female preference on the number of spots on male guppies? use sexual selection to explain the results.
use the link to the simulator as well https://leosiiman.neocities.org/lab-guppy/guppy-lab
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what did endler’s investigation on selection in guppy fish prove? x3
females prefer to mate with ‘flashier’ males (more orange spots on their tails)
flashier males may also be more visible to predators and be more likely to be eaten
what are the two guppy predators? in what parts of the river do they live? which one is more agressive (how does their diet reflect this)?
rivulus “killifish” = higher elevation (begging of guppy streams), less vicious as they only eat young guppies
pike cichlids = lower elevations (larger deeper stretches of guppy streams), more vicious as they eat 4-5 guppies daily
how did guppies differ in high vs low predation habitats? x3 ways
larger in low predation, smaller in high predation
more colourful in low predation, less colourful in high predation
less babies in low predation, more babies in high predation
why are models used in science? x3
can simplify complex processes/concepts
change the scale of objects/processes that are too big/small to be seen
change the rate of a phenomenon (slow down/speed up)
define allele
different versions of the same gene
define gene pool
the collection of all the genes and the various alleles of those genes within a population
define gene flow
any movement of individuals, and/or the genetic material they carry, from one population to another
what effect does gene flow have within a population?
can introduce new alleles to a population, increasing the genetic variation of that population
what effect does gene flow have across populations?
can make distant populations genetically similar to one another, hence reducing the chance of speciation
define allele frequency
prevalence of a specific allele out of all alleles for a gene in a gene pool
the frequency of the alleles of a gene must equal what?
1
how to calculate allele frequency
dividing the number of times a specific allele is observed in the population by the total number of all alleles for that gene in the population
(see slide 73)
define genetic shift as a change in allele frequency
when a population is altered due to random events, such as natural disasters. the surviving individuals are a sample of the original population and their allele frequencies may be very different than other populations
define founder effect as a change in allele frequency
a type of genetic drift (chance event) that occurs when a small group of migrants—not genetically representative of the population from which they came—establish in a new area. the new population will have different allele frequencies than the original population
define natural selection as a change in allele frequency
different populations may have different selection pressures acting on the alleles within the gene pool, maintaining alleles that provide an advantage and selecting out alleles that negatively impact survival and/or reproduction
define new mutations as a change in allele frequency
new alleles produced by changes in the DNA. any new allele in the gene pool causes a change in the frequency alleles in a population relative to a population in which the mutation did not occur
define neo darwinism
a cohesive theory of evolution that integrates darwin’s idea of natural selection with understandings of genetics and gene pools of populations
what does neo darwinism include x4 elements
the molecular variation in DNA between individuals
with how those variations are inherited through cells
with the differential survival and reproduction of organisms
with the ultimate change a population over time.
visible indicator that a gene is NOT evolving
if allele frequency of a specific gene in a population remains stable over time
what are the 5 processes that can alter allele frequencies
mutation
gene flow
nonrandom mating
genetic drift
selection
the long term effect of a mutation on allele frequencies depends on what?
the allele’s fitness
is gene flow is more likely to have a strong effect on allele frequencies on smaller or larger populations?
smaller
examples of nonrandom mating x3
sexual selection (chosen by genetic traits)
mating with closer neighbours than distant members of population
choosing mates that are most like themselves
what can genetic drift cause in terms of alleles in a population? x2
rare alleles to become more common in a population
some alleles to disappear entirely
what are three patterns of evolutionary change that result from natural selection?
stabilizing selection
disruptive selection
directional selection
(see slides 93 to 96 for visuals)
how does stabilizing selection curve change with natural selection?
reduces phenotypic variation in the population by selecting against the extreme varieties at each end of the phenotypic range (makes the bell curve narrower (reduced phenotypic range))
how does directional selection curve change with natural selection?
favours individuals with phenotypes at one extreme of the phenotypic range. common during periods of environmental change (bell curve shifts in the direction of the selected phenotype)
how does disruptive selection curve change with natural selection?
favours individuals with phenotypes at both extremes of a phenotypic range while removing those with intermediate varieties. (starting bell curve shapes results in what looks like two bell curves side by side and merged in the middle)
6 steps to using the hardy-weinberg equation
find q² (dd/total number)
take the square root of q² to find q.
determine p by subtracting q from 1 (p= 1 - q)
determine p² by multiplying p by itself
determine 2pq by multiplying p time q times 2 (2pq = 2 x p x q)
check that your calculations are correct by checking the values for p and q in the hardy-weinberg equations
in order for a population to be in hardy-weinberg equilibrium, what conditions must be met? x5
the population is large to minimize impact of changes due to chance (genetic drift)
there is random mating between organisms
natural selection is not favouring one phenotype over another
there are no new mutations, so new alleles are not generated
there is no gene flow (emigration or immigration)
how many generations of allele frequencies of a gene are compared to determine if a population is either in hardy-weinberg equilibrium OR is evolving?
at least 2
