Evolution Lecture 3 Flashcards
(37 cards)
How many genes do animals and plants have in their genome?
Tens of thousands
Locus
Where the two alleles are.
Population
Localised group of interbreeding and interacting individuals (sexual species). Each species is made up of one to many populations (that can interbreed when
they meet). Members of on population is more closely related than a different population. Typically they are separated by distance.
Who are species in a population move likely to breed with?
Other people in the population, but occasionally won’t (interbreeding). Typically the frequency of the alleles between the populations are different.
Gene Pool
All alleles at all gene loci in all individuals. Shows the total genetic variability or potential in a population.
Fixed alleles
Whole population is homozygous at locus.
Polymorphic loci
2+ alleles in population, each present at some frequency. They can be present equally or one is rare and one is common. Most populations have
thousands of polymorphic loci. This is where we have genetic variation and where natural selection happens.
Source of genetic variation?
Mutation and gene duplication.
Mutations
New alleles arise by mutation in existing alleles.
(A single mutation can result in a new allele). This is a change in a base pair.
How can mutations impact the environment?
Most mutations don’t meaningfully affect fitness
a ‘neutral variation’ (neutral alleles). It doesn’t matter if you have the mutation or not. The most it could do is change the phenotype.
Some reduce fitness: harmful alleles (a.k.a. ‘deleterious’ mutations/alleles). Because organisms reflect many generations of past selection, their phenotypes are ones best suited for there environment, so most new mutations are at least slightly harmful.
*A very few increase fitness: beneficial alleles. These are the least likely to occur (eg. warfarin rats)
In animals what happens to. the mutations?
They mostly occur in somatic called and aren’t passed on to the offspring.
Why does HIV get more mutations?
It has an RNA genome which causes more mutations because it lacks a RNA repair mechanism in host cells. This means single drug treatments are unlikely to be effective against HIV, but a mix of medications is likely to work better.
Gene Duplication
Duplication of smaller pieces of DNA may not be harmful, these can get passed on to generations, allowing mutations to accumulate. Resulting in an expanded genome with new genes that may take on new functions.
How could gene flow be introduced?
By other population, which made the mutation.
Microevolution
Change in the frequencies of alleles over generations. At the extreme, ‘change’ can mean fixation of an allele, or loss (extinction) of an allele. It’s evolution on a small scale.
How to calculate genotype frequencies?
of individuals with the genotype / # of total organisms
P and q in allele frequencies?
If possible p is dominant and q is recessive.
Hardy-Weinberg Principle
Describes expected relationships between allele and genotype frequencies when there is no evolution under certain assumptions. If we compare what we calculated with what occurred and they are equal, this suggests the population isn’t evolving. In populations that are not evolving, allele and genotype frequencies will remain constant from each generation.
What must occur for evolution to occur?
An individual must differ genetically, the presence of genetic variation does not guarantee that a population will evolve.
Random mating
Taking two random alleles out of the population pool, sticking them together to get the combination of alleles in any new individual in that population.
The math Hardy-Weinberg Principle
p2 + 2pq + q2 = 1.
p2, q2 = Expected frequencies of the two homozygote genotypes
2pq = Expected frequency of heterozygotes
Using Hardy-Weinberg principle?
1) Estimating allele and genotype frequencies. e.g. Prevalence of carriers (heterozygotes) of recessive genetic disorders. This is done by using just one of the frequency of one of the homozygous genotypes.
2) Populations with genotype frequencies that conform to the equation are said to be in Hardy-Weinberg equilibrium at that locus. Look at population genotype frequencies to see if they are actually in Hardy-Weinberg equilibrium
Assumptions of Hardy-Weinberg
It’s how we can have population where the genotype and allele frequencies don’t correspond.
1)No net mutations
2) Random mating
3) No natural selection
4) Very large (infinite) population size
5) No migration (no loss or more coming in of a individuals from a population).
Violation of these assumptions usually signals evolutionary change
Example of non-random mating?
How plants can be both mother and father. This is called stealthing, this leading to lower frequencies of heterozygotes.
