(18) population and evolution

Question 1

define species

Answer 1

a group of similar organisms that can reproduce to give fertile offspring

Question 2

define population

Answer 2

a group of organisms of the same species living in a particular area at a particular time (potential to interbreed)

Question 3

what is a gene pool

Answer 3

complete range of alleles present in a population

Question 4

what is allele frequency

Answer 4

how often an allele occurs in a population (usually given as a % of the total population)

Question 5

how can the hardy weinberg equation be used to predict allele freq (if you know the freq of one allele)

Answer 5

p + q = 1 where p is the freq of the dominant allele and q is the freq of the recessive one

Question 6

what is the equation for predicting the freq of one genotype when you know the frequencies of the others

Answer 6

p^2 + 2pq + q^2 = 1
p^2 = freq of homozygous dominant
2pq = freq of heterozygous genotype
q^2 = freq of homozygous recessive genotype

Question 7

what are the conditions needed for the hardy weinberg principle to apply

Answer 7

1. large population
2. no immigration / emigration
3. no mutations
4. no natural selection
5. random mating

Question 8

what causes genetic variation within a species

Answer 8

individuals of the same species having different alleles of the same genes. this is due to mutations, independent segregation (during meiosis) or random fertilisation

Question 9

what is evolution

Answer 9

change in allele freq over time

Question 10

how does natural selection work

Answer 10

variation means some are more adapted to selection pressures than others. individuals with a phenotype that increases their chances of survival are more likely to reproduce so there will be higher freq of beneficial alleles in gene pool

Question 11

what is stabilising selection

Answer 11

individuals with alleles for characteristics towards middle of range are more likely to survive and reproduce occurs in a non changing environment and reduces possible range of phenotypes

Question 12

what is directional selection

Answer 12

individuals with alleles for a single extreme phenotype are more likely to survive and reproduce usually in response to an environmental change

Question 13

what is disruptive selection

Answer 13

individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce. characteristics towards middle of range are lost and occurs when environment favours more than one phenotype.

Question 14

define speciation

Answer 14

development of a new species from an existing species

Question 15

when does speciation occur

Answer 15

when populations of the same species become reproductively isolated with or without physical separation

Question 16

what is allopatric speciation

Answer 16

when a physical barrier e.g. flood or earthquake divides population causing some individuals to become separated from main population. (geographical isolation)
different alleles would be more advantageous in diff populations.

Question 17

what is sympatric speciation

Answer 17

random mutations can occur within population preventing interbreeding e.g. if a polyploid organism emerges in a diploid population.
seasonal- individuals from same population develop different flowering or mating seasons
mechanical- changes in genitalia prevent mating
behavioural- group of individuals develop courtship rituals that aren’t attractive to main population

Question 18

what is genetic drift

Answer 18

when chance rather than environmental factors dictates who survives and reproduces. eg by chance the allele for one genotype is passed on more frequently than others. change in allele freq between 2 isolated populations could lead to reproductive isolation / speciation

Question 19

why does genetic drift have a greater effect in smaller populations

Answer 19

because chance has a greater influence but in larger populations any chance variations in allele freq tend to even out across the whole population