vaiation and evolution

Question 1

what are the two types of variation?

Answer 1

continuous- eg height
discontinuous- eg blood group

Question 2

selection pressure

Answer 2

an environmental factor that can alter the frequency of alleles in a population, when it is limiting

Question 3

natural selection

Answer 3

the increased chance of survival and reproduction of organisms with phenotypes suited to their environment enhancing the transfer of favourable alleles from one generation to the next

Question 4

gene pool

Answer 4

all alleles present in a population at a given time

Question 5

allele frequency

Answer 5

number of times an allele occurs within the gene pool

Question 6

selective advantage

Answer 6

characteristic that enables an organism to survive and reproduce better than other organisms within a population in a given environment

Question 7

factors that can alter allele frequency and cause changes to the gene pool

Answer 7

• genetic drift
• mutations
• natural selection

Question 8

genetic drift

Answer 8

chance variations in allele frequencies in a population
- important evolutionary mechanism in small or isolated populations

Question 9

founder effect

Answer 9

• few individuals become isolated from rest of species and start new population eg colonising a new habitat or island
• founder members are small sample of (original) population
• may have diff gene frequency
• may undergo genetic drift
• may become diff from original population

Question 10

founder effect defn

Answer 10

loss of genetic variation in a new population established by a very small number of individuals from a larger population

Question 11

species

Answer 11

group of individuals with similar characteristics that can interbreed to produce fertile offspring

Question 12

isolation

Answer 12

occurs when a barrier prevents two populations from breeding with one another

Question 13

speciation

Answer 13

evolution of new species from existing ones

Question 14

allopatric speciation- geographical

Answer 14

• population is physically split into separate breeding groups (demes)
• so diff environmental conditions that favour diff individuals within each deme
• after many generations exposed to the diff conditions, allele frequencies change within the demes due to diff mutations
• if barrier removed they have changed so much they can no longer interbreed

Question 15

sympatric speciation- reproductive

Answer 15

• when organisms inhabiting the same area become reproductively isolated into two groups when there are no physical barriers
  examples
• seasonal isolation- diff reproductive cycles
• mechanical - incompatible genitalia
• gametic- failure of pollen grains to germinate on stigma or sperm fail to survive in oviduct

Question 16

natural selection- darwinian evolution based on:

Answer 16

• evolution is the process by which new species are formed from pre existing ones over a long period of time
• there is already variation within the population brought about by mutation
• ___________ with the beneficial alleles have a selective advantage
• these individuals can reproduce more successfully
• can pass on that favourable allele to offspring
• beneficial allele frequency increases within the gene pool

Question 17

hardy weinberg principle

Answer 17

in ideal conditions the allele and genotype frequencies in a population are constant

Question 18

assumptions of hardy weinberg

Answer 18

• population is large (if small chance events can cause large changes in allele frequency) and there is no migration or immigration ( movement would lead to new alleles entering or leaving gene pool)
• random mating between individuals
  and genotypes must have same reproductive success ( ensures there is an equal probability of any allele of a gene being passed to the next generation)
• no mutation