18.Populations And Evolution Flashcards
What is a population
Group of organisms of same species that occupy a particular space at particular time and ca potentially interbreed
What is gene pool
All alleles of all genes of all individuals in a population at a given time
What is allelic frequency
Number of time the allele occurs within the gene pool
What assumptions are made when using hardy Weinberg
No mutations arise
Population is isolated, no flow into or out
No selection, all alleles likely to be passsed on
Population is large
Mating is random
What are the equations of Hardy Weinberg
When A (dominant) = p
P+q=1.0
P^2 + 2pq + q^2 = 1.0
What are genetic variations due to
Mutations - sudden changes to genes or chromosomes
Meiosis - nucleic division of gametes, new combinations of alleles
Random fertilisation of gametes - sexual reproduction, new combo of alleles, random fertilisation of gametes
How does environmental influence variation
Exerts influence on way the organisms genes are expressed, determines where organisms lie on continuum
What does process of evolution by natural selection depend upon
- organisms producing more offspring than can be supported by the available supply of food light space
- there’s genetic variation within population of all species
- variety of phenotypes that selection operates against
What is role of over production of offspring in natural selection
Populations have evolved high reproductive rates in order to ensure sufficiently large amount of population survives to breed and produce next generation, to compensate for high death rates by predation, food comp, natural disasters
What’s the link between over production and natural selection
When there’s too many offspring for available resources, there’s competition amongst individuals (intraspecific) for limited resources, the greater the numbers the greater the competition, the more individuals die in struggle to survive
What’s role of variation in natural selection
- Larger population
- more genetically varied the individuals
- greater chance that one or more possess combo of alleles that lead to advantageous phenotype
- more likely to breed and pass on allele combinations
- survival will favour those with advantageous alleles
What are the 3 types of selection
Stabilising selection
Directional selection
Disruptive selection
What is stabilising selection
Preserves average phenotype of population by favouring average individuals, favour against the extremes
What is directional selection
Changes phenotypes of population favouring phenotypes that vary in one direction from mean of population, selection for extreme phenotypes
What is disruptive selection
Favours individuals with extreme phenotypes rather than those the phenotypes around the mean of population.
What is speciation
Evolution of new species from existing ones
What is allopatric speciation
When two populations become geographically separated, may be physical barrier, if environmental conditions either side of barrier vary, natural selection will influence two populations differently.
Each will evolve differently due to different conditions
What’s sympatric speciation
Form of speciation that occurs within a population in same area leading to them becoming reproductively separated
What are the 5 forms of isolating mechanisms
Geographical - physical barriers
Ecological - populations inhabit diff habitats in same area, don’t meet
Temporal - breeding seasons don’t coincide
Behavioural - mating mutations that lead to no courting
Mechanical - anatomical differences that prevent mating eg penis can’t fit
Gametic - failure of gametes meeting or biochemical incompatibility
Hybrid sterility - hybrids formed by fusion of two gametes from seater species
What are the effects of each form of selection on evolution
Stabilising-reduces number of extreme phenotypes and so little variation in characteristics so no evolution
Directional-favours new optimum phenotype, therefore evolution to a degree
Disruptive-over many years it will form two different species as they evolve to favour two opposite extreme characteristic
How does natural selection affect allelic frequency
Selection due to environmental factors, Environmental changes affect probability of allele being passed on in population and hence number of times it occurs in gene pool
How do new species form
- Individuals tend to breed within same population but can with other populations
- if one population is separated and undergoes different mutation it will be genetically different
- each populations experience different selection pressures due to different environments
- natural selection leads to change in allelic frequencies
- adaptive radiation-when each populations adapts to local environment
- change in allelic frequencies of each population, each with its one gene pool - different species
