populations and evolutions

gene pool

all the alleles in a population

population

organisms of one species in a habitat/ecosystem

community

organisms of all species in a habitat/ecosystem

abiotic factors definition

non-living factors

how can resistance appear in an isolated population of organisms

mutation

how could you determine if two organisms from different populations belongs to the same species

breed together

• if fertile offspring: then same species

evolution

• variation present in original population

• mutation occurs

• individuals with advantageous alleles become better adapted for survival and are more likely to survive and reproduce

  • greater reproductive success

• pass on allele to offspring

• frequency of allele increases in offspring and next generation

  • takes many generations for favourable allele to become the most common allele

  • allele frequency changes

allopatric speciation

• geographical isolation

• gene pools are separate and no interbreeding

• variation present in population, due to mutation

• different selection pressures and differential reproductive success leads to change in allele frequency & gene pools over time

sympatric speciation

• speciation occurs in the same habitat/environment/population

• mutation occurs

• mutation causes difference in reproductive/mating habits (usually mentioned in the questioned)

• reproductive isolation (e.g. different breading seasons)

  • no interbreeding

  • gene pools remain separate

  • no gene flow

• change in frequency of alleles

  • different alleles passed on

• eventually become different species & unable to produce fertile offspring

  • divergence of gene pools

  • gene pools become increasingly different until they cannot interbreed to produce fertile offspring

Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium.

1. frequent use of antibiotic kills bacteria & creates selection pressure

2. bacteria with mutation have selective advantage over others

3. these bacteria are more likely to survive and reproduce than other types of bacteria, allowing them to pass on advantageous alleles in greater numbers

4. frequency of advantageous alleles increases in subsequent generations

5. frequency of resistant types of bacteria increase in subsequent generations

directional selection

• dominant allele confers advantage

  • dominant allele more likely to survive and reproduce

• recessive allele confers disadvantage

stabilising selection

only few organisms survive at the extreme

• most survive from middle of the range

what does the Hardy-Weinberg principle predict?

that the frequency of alleles will stay constant/the same, provided that theres no mutation

5 assumptions that must be made when using the hardy-weinberg equation

1. no selective advantage

2. large population

3. random mating

4. no mutation

5. no immigration/emigration

A population of summer squash plants produced only green and yellow fruit. The percentage of plants producing yellow fruit in this population was 36%.

Use the Hardy-Weinberg equation to calculate the percentage of plants that were heterozygous for gene B.

• yellow fruits are produced either with genotype aaBb or aaBB

  • since we dont know which one the yellow fruit in the question has, we should take a look at the green fruits that were produced instead, since we know for a fact that they were produced with a genotype aabb

• green fruit = 1-0.36 = 0.64

• p²= 0.64

• p = 0.8

• p+q=1

• q=0.2

• heterozygous: 2pq

• 2×0.8.0.2 = 0.32 × 100

• answer: 32%

give 4 conditions necessary for results from mark-release-recapture investigations to be valid.

1. no migration/immigration

2. no reproduction

3. large enough sample size

4. marking doesn’t increase vulnerability to predation

capture-recapture method

• capture/collect sample

• mark and release

• ensure that method of marking doesn’t:

  1. harm lizard

  2. makes it more visible to predators

• leave sufficient time for lizards to randomly distribute in island, before collecting a second sample

• population = number in first sample x number in second sample / number of marked lizards in 2nd sample

how succession occurs

• colonisation by pioneer species

• change in the environment, which enables the other species to survive and colonise

• change in biodiversity

• stability increases

  • becomes a less hostile environment

  • climax community