Topic 7 - Populations and Evolution Flashcards
(41 cards)
what is a population
a group of organisms of the same species living in a particular area at a particular time.
what is a gene pool
the complete range of alleles in a population
what is allele frequency
how often an allele occurs in a population
what does the Hardy-Weinberg principle predict
- allele frequencies wont change from one generation to the next
- if it is a large population..
- no immigration
- no emigration
- no mutations
- no natural selection
- random mating
in the Hardy Weinberg principle, what does p^2 stand for
frequency of homozygous dominant genotype
in the Hardy Weinberg principle, what does 2pq stand for
frequency of heterozygous genotype
in the Hardy Weinberg principle, what does q^2 stand for
frequency of homozygous recessive genotype
what is the hardy weinberg equation
p^2 + 2pq + q^2 = 1
what is genetic variation
all the different alleles of genes in a population
what is the main source of genetic variation
mutation
what is evolution
the change in allele frequncy over time
what is disruptive selection
- individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce
- e.g. birds with large beaks are specialised for large seeds. birds with small beaks are specialised for small seeds
what is speciation
the development of a new species from an existing species
when does speciation occurs
- when a population of the same species becomes reproductively isolated
- by a physical barrier - allopatric
- by a reproductive barrier - sympatric
how does allopatric speciation work
- population is geographically separated
- the population willl experience different selection pressures
- random mutations will occur
- different alleles will be more advantageous in different populations
- allele is passed onto offspring
- this changes the allele frequency which leads to different phenotypes frequencies
- eventually the populations will change so much that they will no longer be able to interbreed and produce fertile offspring - reproductively isolated
why does sympatric speciation occur
- seasonal - develop different flowering or mating seasons
- mechanical - changes in genitalia prevent successful mating
- behavioural - develop a courtship ritual that are not attractive
- this all leads to reproductive isolation
how does sympatric speciation occur
- in the same area
- random mutation results in a new phenotype
- passed down to offspring
- allele frequency increases
- causing reproductive isolation
- eventually they become different species
- cannot produce fertile offspring
what are selection pressures
external factors that impact reproductive success of an individual
what is the genetic drift
- individuals within a population show variation in their genotypes
- by chance the allele for one genotype is passed on to offspring more often
- so the number of individuals with the alleles increases
- changes in the allele frequency in two isolated populations could eventually lead to reproductive isolation and separation
- this causes evolution
what is a community
populations of different species living in the same habitat at the same time
what is an ecosystem
a community and all the non living conditions in the habitat
what is a niche
the role of a species in a habitat, e.g. what it eats, where it feeds
why is it good that different species in an ecosystem have different niche
- they dont have to compete for food
- so they can both survive and reproduce
what are examples of abiotic factors
- light
- water
- space
- temperarure
- chemical composition
