3.7.3 evolution may lead to speciation

Question 1

Wide range of variation caused by

Answer 1

Genetic factors
- mutations: change in DNA base sequence > new allele
- meiosis: crossing over, independent segregation

Environmental factors: climate wahever

Question 2

Evolution

Answer 2

Change in allele frequency in a population over time

1. variation within a pop due to mutations
2. Selection pressure e.g. comp > struggle for survival
3. Some organisms have phenotypes providing selective adv (due to favourable alleles)
4. Organisms more likely to survive and reproduce, passing favourable allele to next gen
5. Allele frequencies in gene pool change over time

Question 3

Directional selection

Answer 3

Selection pressure acts on one side of the mean

Mean shifts in direction of favourable allele (new mean)

Question 4

Stabilising selection

Answer 4

Selective pressure acts against two extremes of characteristic

Individuals with extreme phenotype less likely to survive > SD smaller over time

Mean stays the same

Question 5

Disruptive selection

Answer 5

Selection against the mean

Population becomes phenotypically divided > favours both extremes of phenotypes

Could result in 2 diff species

Question 6

Speciation

Answer 6

Development of a new species from existing species

Reproductive separation of 2 populations can result in accumulation of differences in gene pools

New species arise when these genetic differences lead to an inability of members of populations to interbreed and produce fertile offspring

Question 7

Allopatric speciation

Answer 7

Geographic isolation - separate gene pools, no interbreeding

Mutations create genetic variation in each pop

Different selection pressures (e.g. predation) acts on each pop

Adapted organisms survive and breed

Change in allele frequency

Question 8

Sympatric speciation

Answer 8

In same area

Genetic variation in pop due to mutations

Results in mechanism that makes individuals reproductively isolated (gene flow is restricted)

Different selection pressures occur > change in allele frequency within gene pools

Members of diff populations cannot interbreed > new species

Question 9

Genetic drift

Answer 9

Mechanism of evolution in which allele frequencies of a population change over generations due to chance

Strongest effects in small populations as chance has a greater influence

Unlike natural selection, doesnt take into account how favourable or harmful an allele is

Major effects when a pop is sharply reduced in size (bottleneck effect) or when a small, new colony forms from a main pop (founder effect)