Module 6 Section 3 - Evolution Flashcards
What is a gene pool?
The complete range of alleles present in a population is called the gene pool.
What is allele frequency?
How often an allele occurs in a population
What is the process for natural selection?
1) individuals within a population vary because they have different alleles. New alleles are generated by mutations in genes.
2) predation, disease and competition (selection pressures) create a struggle for survival.
3) due to individuals being different, some are better adapted to the selection pressures than others.
4) individuals with advantageous alleles are more likely to survive and reproduce and pass on the advantageous allele than individuals with other alleles.
5) this means a greater proportion of the next generation inherit the advantageous allele.
How does selection occur in a stable environment?
When the environment isn’t changing much, individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. This is called stabilising selection and it reduces the range of possible phenotypes.
How does selection occur in a changing environment?
When there is a changing environment, individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce. This is called directional selection.
How does evolution occur via genetic drift?
1) Individuals within a population show variation in their genotypes.
2) by chance, the allele for one genotype is passed on to the offspring more often than others. So the number of individuals with the allele increases.
3) if by chance the same allele is passed on more often again ans again, it can lead to evolution as the allele becomes more common in the population.
4) this is more likely to happen in smaller populations, where chance has a greater influence.
What is a genetic bottleneck?
A genetic bottleneck is an event (such as a natural disaster) that causes a big reduction in a population’s size, leading a reduction in a gene pool. Evolution by genetic drift has a greater effect is there’s a genetic bottleneck.
What is the founder effect?
The founder effect described what happens when a few organisms from a population start a new population and there’s only a small number of different alleles in the initial gene pool.
How does the founder effect work?
1) Individuals within a population show variation in their genotypes.
2) some of these individuals start a new population. By chance these individuals most have one particular genotype.
3) without further “gene flow”, the new population will grow with reduced genetic variation. As the population is small, it’s more heavily influenced by genetic drift, than a larger population.
4) the founder effect can occur as a result of migration leading to geographical seperation or a new colony is separated from the original population.
What is the hardy- Weinberg principle?
It is a mathematical model which predicts that the frequencies of alleles in a population won’t change from one generation to the next, under certain conditions.
What are the conditions for the the hardy Weinberg principle?
1) it has to be a large population where there’s no immigration, emigration, mutations of natural selection.
2) there needs to random mating, all possible genotypes can breed with all others.
What is the equation for allele frequency?
p + q= 1
p= the frequency of the dominant allele
q=the frequency of the recessive allele
What is the equation for genotype frequency?
p^2 + 2pq + q^2= 1
p^2= frequency of homozygous dominant genotype.
2pq= frequency of heterozygous genotype.
q^2= frequency of homozygous recessive genotype.
What is artificial selection?
Artificial selection is when humans select individuals in a population to breed together to get desirable traits.
How to breed for desirable traits in cattle?
1) farmers select a female with a very high milk yield and a male whose mother had a very high milk yield and breed these two together.
2) then they select the offspring with the highest milk yields and breed them together.
3) this is continued over several generations until a very high milk-yielding cow is produced.
What are positive characteristics in dairy cows?
A high milk quality
A long lactation period.
Large udders
Resistance to mastitis
A calm temperament
How to breed plants for a high yield?
1) Wheat plants with a high wheat yield are bred together.
2) the offspring with the highest yields are then bred together
3) this is continued over several generations to produce a plant that has a very high yield.
What are positive characteristics of wheat?
A higher tolerance of the cold and other wheat varieties
Short stalks
Uniform stalk heights
What are the problems with artificial selection?
1) reducing the gene pool
2) health problems for organisms
3) ethical issues
How does artificial selection reduce the gene pool + problems?
Artificial selection means that only organisms with similar traits and similar alleles are bred together. This leads to a reduction in the number of alleles in a gene pools.
A reduced gene pool could cause problems in the future eg if a new disease appears, there’s a lower chance of resistance to the disease being present in the alleles. Artificial selection also means that potentially useful alleles are lost from the population.
This means it’s important to maintain resources of genetic material for use in the future, for example preserving the original “wild type” organisms that haven’t undergone any artificial selection.
Why is it important to maintain viable wild populations of crop plant species?
1) need for genetic variation
2) genetic resource / gene bank
3) source of useful alleles
4) can be cross bred with crop varieties
5) allows introduction of different traits
6) unknown future requirements
7) potentially useful in changing climate
8) prevention of inbreeding depression
9) prevent dwindling gene pool
10) source of replacement if cultivated population is in danger
How does artificial selection have ethical issues?
1) many people don’t think it’s fair to keep artificially selecting traits in dogs that cause them health problems.
2) it’s also immoral to neglect breeds that do not have the same desirable traits that are being bred.
What is a species?
A group of similar organisms that can reproduce to give fertile offspring
What is speciation?
The development of a new species
What is allopatric speciation?
Populations can become reproductively isolated though a combination of geographical isolation and natural selection.
How does geographical isolation cause a species to become reproductively isolated?
1) Geographical isolation happens when a physical barrier eg a flood, divides a population of a species, causing some individuals to become seperated from the main population of a species.
2) populations that are geographically isolated experience slightly different conditions eg different climates, so different characteristics will become more common due to natural selection because there are different selection pressures.
3) the alleles that are more advantageous on each side will become more frequent , which will lead to changes in phenotype frequencies.
4) eventually, individuals from different populations will have changed so much that they won’t be able to breed with one another to produce fertile offspring. Therefore they are reproductively isolated and become two seperate species.
How does reproductive isolation occur?
1) seasonal changes- individuals from the same population develop different flowering or mating seasons, or become sexually active at different times of the year.
2) mechanical changes- changes in genitalia prevent successful mating
3) behavioural changes- a group of individuals develop courtship rituals that aren’t attractive to the main population.
What is sympatric speciation?
Speciation due to reproductive mechanisms, without geographical isolation
How can sympatric speciation lead to reproductive isolation?
Random mutations could occur within a population causing seasonal, mechanical or behavioural chnages, preventing members of that population breeding with other members of the species.
What conditions must be present for speciation to occur?
1) reproductively isolated
2) time
3) genetic diversity/mutation
4)directional/natural selection
5) environment different from other population
