3.7.3 Evolution May Lead To Speciation Flashcards
What factors cause individuals in a population to show variation in phenotype
Genetic and environmental factors
What causes genetic variation
Mutations, main source of variation, sudden change in genes, may or may not be passed on
Meiosis, produced new combinations of alleles before they pass into gametes, all are different
Random fertilisation of gametes, any gamete from one parent can fuse with any gamete from the other parent, new combinations of alleles, adds to variety of offspring
Sexual reproduction uses all 3 methods
What are environmental factors
Climate conditions like rainfall sunlight and temp
Soil conditions
pH
Food availability
Variation is mainly due to a combination of genetic differences and environmental influences
What are selection pressures give examples
Environmental factors which limit the population of a species
Predation
Disease
Competition
Process of the evolution by natural selection
Species have high death rates due to predation, competition and disease, so increased their reproductive rate to produce the next generation.
Too many offspring lead to infraspecific competition
Organisms best suited to the environmental conditions are more likely to survive, more likely to breed, pass on favourable alleles to next generation
New generation have a different allele frequency from previous generation
What’s stabilising selection and its effect
Preserves the average phenotypes of a population
Occurs when environmental conditions are constant over a long period of time
Eg human birth weight, babies with extreme weights are more likely to die
Standard distribution curve becomes tall and skinny as more organisms are the closer to the mean
What’s directional selection and its effect
Changes phenotypes of a population by favouring one extreme phenotype
If environmental conditions change, optimum value for survival will too, individuals at either extreme will posses alleles with a new optimum phenotype
Eg antibiotic resistance in bacteria
Normal distribution curve translated left or right
What’s disruptive selection and its effect
Favours individuals with both extremes
Brings about evolutionary change
Environmental factors take two distinct forms
Eg temp might be 5° in winter and 20° in summer, two seperate species
Normal distribution curve forms two peaks at the extreme ends (McDonald arches)
What’s evolution
Change in allele frequencies in a population
What’s a species
Group of individuals with common ancestry (share same genes but different alleles) and are able to breed to produce fertile offspring
What’s speciation
Evolution of a new species from existing ones
What’s reproductive separation
Changes in alleles and phenotypes of some individuals preventing them from breeding with others in the population
How does a new species arise
Reproductive separation, a population becomes separated from other populations
Undergoes different mutations, each population becomes genetically different from the others
Each population experiences different selection pressures due to different environments
Natural selection leads to changes in allele frequency of the populations
Phenotypes are due to different alleles and selection pressures
Each population is adapted to environment, new species are formed as each population can no longer interbreed with eachother
What’s genetic drift
Occurs in small populations, less variety in alleles, not an equal chance of all alleles being passed on, alleles passed on have a high allele frequency, mutations will affect the population, greater effects of genetic drift, more likely to develop into seperate species
In a large population effects of mutation will be diluted due to a lower allele frequency bc of a larger gene pool
What are two types of speciation
Allopatric
Sympatric
What’s allopatric speciation
Two populations become geographically seperated
Environmental conditions each side of the barrier vary, natural selection influences the two populations differently, adapt to local conditions, reproductive separation, seperate species are formed
What’s sympatric speciation
Populations in the same area leading to reproductive separation
Individuals favour different habitats in the same area or have different behaviour, reproductive separation, mutations, unable to interbreed forming new species
