Evolution - M6 Flashcards
2 types of variation and their causes
Continuous = Genetic + Environment
Discontinuous= Genetic , environment has little or no effect
how to represent continuous data biology
Histogram
how to represent discontinuous data biology
Bar chart
Gene pool =
The sum total of all the genes in a breeding population at any given time
Allele frequency =
The relative frequency of a particular allele in a population
is The frequency with witch an allele occurs in a population related to weather it is dominant or recessive ?
No
Population genetics
The study of the gene pools, and the allele and genotype frequencies of populations of organisms
The environment influences the expression of polygenetic traits ____ than monogenetic traits
More
Stabilising selection
When environment isn’t changing much, indivs with alleles for characteristics towards the middle of the range (e.g: short fur to long fur) are more likely to survive + reproduce.
Thus reducing range of possible phenotypes. keeping allele frequencies constant
maintenance of the intermediate
Stabilising selection is natural selection that keeps allele frequencies relatively constant over generations
This means things stay as they are unless there is a change in the environment
Directional selection
Directional selection is natural selection that produces a gradual change in allele frequencies over several generations
This usually happens when there is a change in environment (and therefore a change in selection pressures) or a new allele has appeared in the population that is advantageous
Process of directional selection
- There is always phenotypic variation within a population
- There is a selection pressure that favours a particular phenotype
- The phenotype is produced by particular alleles
- Individuals with the favoured phenotype are fitter and so more likely to reproduce and pass on the advantageous alleles to their offspring
- Those who do not possess the advantageous allele or phenotype are less likely to survive and pass on their alleles to their offspring
- So over time and several generations the frequency of the advantageous allele increases and the frequency of other alleles decreases
Disruptive selection
When change in environment, indivs with alleles for characteristics of TWO extreme typeS are more likely to survive + reproduce
Howe is evolution via genetic drift different to evolution via natural selection?
Characteristics become more common by chance, rather than (In natural selection) they increasing an organisms likelihood of survival
Process of Evolution via genetic drift
-Indivs in population show variation in their genotypes
-By chance , the allele for one genotype is passed on to the offspring more than others. So the number of indivs with that allele increases
-if by chance , the same allele is passed on more often again and again, it can lead to evolution as the allele becomes more common in the population
Three factors affecting genetic drift
-Population size
-Genetic Bottleneck
-The founder effect
How does Population size effect Genetic drift
-Genetic drift usually has a greater effect on smaller populations where chance has a greater influence
-In larger populations, any chance variations in allele frequency even out across whole population
How does Genetic Bottleneck effect Genetic drift
An event (e.g: natural disaster) causes big reduction in pop. size = reduce gene pool.
Evolution via genetic drift has higher effect here.
-Takes thousands of years for genetic diversity to develop in a population thru slow accumulation
An example of a smaller change to a population size
Gene flow caused by mutation
How does The founder effect effect Genetic drift
-Indivs in a pop. show variation in genotype
-Some indivs start new pop. + by chance have mostly one genotype
-Now further ‘gene flow’ new pop. will grow with reduced genetic variation
-As pop. is small, more heavily influenced by genetic drift than larger pop.
Hardy-Weinberg principle stastes
in a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution
when does Hardy Weinberg principle not apply
any situation which disrupt genetic equilibrium
when assumptions (on other fc) are not applied)
Conditions for Hardy-Weinberg principle to apply
1) No selection (pressure)
2) No mutations
3) Large population size
4) Random mating
No migration
Formula for prediction ALLELE frequency
P + q = 1
Dominant = p
Recessive = q
Formula for prediction GENOTYPE frequency
P^2 + pq + q^2 = 1
P^2 = Homozygous Dominant
pq = heterozygous
q^2 = homozygous recessive
Artificial selection
When humans select individuals in a pop. to breed together to get desirable traits
(selection over many generations leeds to new breeds.)
how are cattle artificially selected
-Farmers select a female with a very high milk yield + male who’s mother had a very high milk yield + breed these two together
-offspring with highest milk yield bred together
-Continued over several generations
outline 2 Problems with Artificial selection
Reducing gene pool
Organism’s health
Artificial selection on Reducing gene pool
-Only animals with similar traits and therefore alleles are bred together therefore decrease number of alleles in gene pool.
= less chance of alleles offering resistance to new diseases being present in the population
When the genetic differences lead to an inability of members of the populations to interbreed and produce fertile offspring, ………. has occurred
speciation
2 types of Speciation
Allopatric speciation
Sympatric speciation
Allele frequency
How often a particular allele occurs within a population
Allopatric speciation
New habitat due to separation
-different selection pressures
-Those with that allele are more likely to survive and reproduce (potentially less favourable in previous habitat)
-Change in allele frequency in gene pool
- no genetic exchange (between separated groups)
-Characteristics are accumulated until a new species is formed
Sympatric speciation
no geographical barrier
Reproductive isolation.
no gene flow occurs between two populations
occurs within same habitat
can occur via:
Ecological separation: different environments in same area (e.g: soil pH)
Behavioural separation: e.g: diff eating which leads to diff attraction to mate, so no reproduction
by mating preferences, Disruptive selection
Commonly caused by a rapid genetic change which causes changes in
-Morphology
-behaviour
-habitat preferences
polyploidy
more than 2 sets of homologous chromosomes
more common in plants
result in
higher yield, improved flavour?, best resistance
(having multiple coppies of same gene reduces risk of recessive mutations causing detrimental effects)
