Mr G bio 4 Gene pools, selection and speciation

Question 1

what is allele frequency?

Answer 1

how often an allele occurs in a population- normally given as a percentage of the whole pop

Question 2

what is a gene pool?

Answer 2

all the alleles in a population

Question 3

what conditions is Hardy weinberg true under?

Answer 3

-large population
-no immigration or emigration
-no mutations
-no natural selection
-random mating

Question 4

what does the H-W principle predict?

Answer 4

the frequency of alleles will stay constant from one generation to the next providing no mutation/ selection etc

Question 5

what are the H-W equations used to estimate?

Answer 5

the frequency of particular alleles, genotypes and phenotypes within a population

Question 6

what are the H-W equations?

Answer 6

p + q = 1
p^2 + 2pq + q^2 = 1

Question 7

what is variation and what is it caused by?

Answer 7

the differences between individuals caused by genetic +/or environmental factors

Question 8

what is the main source of genetic variation?

Answer 8

mutation or crossing over of chromatids, independent assortment and random fertilisation of gametes

Question 9

what is evolution?

Answer 9

where the frequency of an allele in a population changes over time which occurs by genetic drift or natural selection

Question 10

what is natural selection?

Answer 10

organisms face selection pressures- affect their chance at surviving and members of same species have diff alleles so some better adapted to survive and and reproduce and pass on the favourable alleles so frequency of beneficial alleles increases

Question 11

what are the 3 types of natural selection?

Answer 11

-stabilising
-directional
-disruptive

Question 12

what is stabilising selection?

Answer 12

-individuals with alleles for charactersistics towards he middle of the range are more likely to survive and reproduce
-selective pressure at both ends of the distribution
-reduces the range of possible phenotypes by eliminating extremes
-occurs when environment is changing

Question 13

what is directional selection?

Answer 13

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

Question 14

what is disruptive selection?

Answer 14

-individuals with alleles from extreme phenotypes more likely to survive and reproduce
-opposite to stabilising as chracteristics towards middle of range are lost
-occurs when the environment favours more than one phenotype

Question 15

what is speciation?

Answer 15

-development of a new species from an existing species
-occurs when populations of the same species become reproductively isolated

Question 16

what does reproductively isolated mean?

Answer 16

changes in allele frequency causes changes in phenotype, which means they can no longer interbreed to produce fertile offspring

Question 17

what is allopatric speciation?

Answer 17

-new species is created when populations are isolated to geographical barriers
-diff selection pressures
-mutations lead to variation which leads to changes in allele frequencies
-no gene flow so populations become reproductively isolated from each other
-cannot reproduce and produce fertile offspring

Question 18

how does a change in allele frequency occur during allopatric speciation?

Answer 18

-variation occurs due to mutations producing different alleles that will be more advantageous in diff populations so there is differential reproductive success
-genetic drift

Question 19

why do changes in allele frequency lead to speciation?

Answer 19

differences in gene pools so changes in phenotype frequencies and eventually phenotypes will be so diff that will be reproductively isolated so new species have been formed

Question 20

in what 3 ways does reproductive isolation prevent breeding?

Answer 20

-seasonal changes
-mechanical changes
-behavioural changes

Question 21

how does seasonal/ temporal isolation prevent breeding?

Answer 21

individuals develop diff flowering or mating seasons or become sexually active at diff times of the year, orgnaisms dont breed as arent reproductively active as same time

Question 22

how does mechanical isolation prevent breeding?

Answer 22

changes in the size or function of genitalia can prevent successful mating, preventing individuals from producing fertile offspring

Question 23

how does behavioural isolation prevent breeding?

Answer 23

a group of individuals may, for example, develop diff courtship rituals that arent attractive to the rest of species

Question 24

what is sympatric speciation?

Answer 24

-occurs when random mutation within a population prevents individuals that carry mutations from reproducing with individuals that dont carry mutation
-occurs in same population (no geographical isolation)

Question 25

what is evolution by genetic drift?

Answer 25

instead of environmental factors affecting which individuals survive, reproduce and pass on alleles, chance dictates which alleles are passed on

Question 26

what is the process of genetic drift?

Answer 26

-individuals within a population show variation in their genotypes -by chance, the allele for one genotype is passed on to more offspring than the others- so no. of individuals with the allele increases -if by chance allele passed on more often again + again then can lead to evolution

Question 27

how does genetic drift lead to speciation?

Answer 27

can lead to differences in allele frequency between 2 isolated populations and if enough differences build up over time then could lead to reproductive isolation and speciation

Question 28

does genetic drift tend to affect smaller or larger populations more? and why?

Answer 28

usually greater effect in smaller populations where chance has greater influence as in larger pops chance tends to even out

Question 29

what impact does genetic drift have on genetic diversity?

Answer 29

causes it to decrease

Question 30

what are the 2 types of genetic drift?

Answer 30

-genetic bottlenecks -the founder effect

Question 30

what is a genetic bottleneck?

Answer 30

-an event causes a big reduction in a population -reduces no. of diff alleles in a gene pool and so reduces allele frequency and genetic diversity -survivors reproduce and larger pop created from a few individuals

Question 31

what is the founder effect?

Answer 31

few organsims from a population start a new colony and only a small no. of diff alleles in initial gene pool -allele frequency in new pop may be very diff to original pop -sometimes leads to higher incidence of genetic disease