Topic 7B - Populations and Evolution DVY *

Question 1

what is a species?

Answer 1

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

Question 2

what is a population?

Answer 2

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

Question 3

what is the gene pool?

Answer 3

the complete range of alleles present in a population

Question 4

what is allele frequency?

Answer 4

how often an allele occurs in a population

Question 5

what is the hardy-Weinberg principle?

Answer 5

a mathematical model that predicts that the frequencies of alleles in a population won’t change from 1 generation to the next

Question 6

what are the conditions of the Hardy-Weinberg principle?

Answer 6

large population
no immigration or emigration (no gene flow)
no mutations
no natural selection
random mating

Question 7

what is the Hardy-Weinberg equation used for?

Answer 7

to calculate the frequency of particular alleles, genotypes and phenotypes within populations.
test whether HW principle applies to particular alleles in particular populations - if frequencies do change there are factors influencing them

Question 8

what is the Hardy-Weinberg equation?

Answer 8

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

Question 9

Hardy-Weinberg equation, how to calculate p from q?

Answer 9

p + q =1

Question 10

what is variation?

Answer 10

the difference that exists between individuals

Question 11

how is there genetic variation within a species?

Answer 11

different alleles of the same genes

this means individuals in a population can show a wide range of different phenotypes

Question 12

how is genetic variation brought about in a species?

Answer 12

mutation - production of new alleles
crossing over and independent segregation in meiosis because of random fertilisation of gametes
Differences in environment

Question 13

How is evolution caused?

Answer 13

Genetic variation - when the frequency of an allele in a population changes over time
and natural selection

Question 14

what is natural selection?

Answer 14

selection pressures create a struggle for survival
due to variation, some are better adapted to selection pressures
individuals with advantageous phenotype more likely to survive, reproduce, pass on genes
greater proportion of next generation inherit beneficial alleles
more likely to survive, reproduce, pass on genes
frequency of beneficial alleles in gene pool increases

Question 15

what are selection pressures?

Answer 15

predation, disease and competition

Question 16

what are the different types of selection?

Answer 16

stabilising
directional
disruptive

Question 17

what is stabilising selection?

Answer 17

where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
reduces the range of possible phenotypes

Question 18

when does stabilising selection occur?

Answer 18

occurs when environment isn’t changing

Question 19

what is directional selection?

Answer 19

where individuals with alleles for a single phenotype are more likely to survive and reproduce.

Question 20

when does directional selection occur?

Answer 20

in response to an environmental change

Question 21

what is disruptive selection?

Answer 21

where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce.
opposite of stabilising selection because characteristics towards middle of range are lost

Question 22

when does disruptive selection occur?

Answer 22

when the environment favours more than one phenotype

Question 23

what is speciation?

Answer 23

the development of a new species from an existing species

this can be caused by disruptive isolation

Question 24

when does speciation occur?

Answer 24

when populations of the same species become reproductively isolated - changes in allele frequency can cause changes in phenotype, which mean they can no longer interbreed to produce fertile offspring

Question 25

what is geographical isolation?

Answer 25

when a physical barrier divides a population of a species, causing some individuals to become separated from the main population.
this leads to allopatric speciation

Question 26

what is sympatric speciation?

Answer 26

when a population becomes reproductively isolated without any physical separation

Question 27

what happens in allopatric speciation?

Answer 27

geographically separated populations experience slightly different conditions e.g. different climate
different selection pressures, so different changes in allele frequencies
differences accumulate in gene pools, causing changes in phenotype frequencies
eventually different populations can’t interbreed to produce fertile offspring they are reproductively isolated
2 groups have become separate species

Question 28

how do separated populations experience different changes in allele frequencies?

Answer 28

different alleles will be more advantageous in different populations
directional selection acts on alleles
allele frequencies change as mutations occur independently in each population
genetic drift may also affect alleles frequencies

Question 29

why don’t species need to be geographically isolated to be reproductively isolated?

Answer 29

random mutations could occur within a population, preventing members of that population breeding with other members of the species

Question 30

why does reproductive isolation occur?

Answer 30

because changes in alleles and phenotypes in some individuals prevent them from breeding successfully with individuals without these changes

Question 31

what changes can cause reproductive isolation?

Answer 31

seasonal - individuals from same population develop different flowering or mating seasons, or become sexually active at different times of year
mechanical - changes in genitalia prevent successfully mating
behavioral - a group of individuals develop courtship rituals that aren’t attractive to the main population

Question 32

what happens in evolution by genetic drift?

Answer 32

individuals within a population show variation in their genotypes
by chance, the allele for 1 genotype is passed on to offspring more often than others
so number of individuals with the allele increases
changes in allele frequency in 2 isolated populations could eventually lead to reproductive isolation and speciation

Question 33

does evolution happen by natural selection or genetic drift?

Answer 33

they can work alongside each other but genetic drift usually has greater effect in smaller populations where chance has greater influence
in larger populations, any chance variations in allele frequency tend to even out across whole population

Question 34

how does the environment influence the way the organisms genes are expressed?

Answer 34

the gene sets the limits for variation

e.g. plant height is dependent on the availability of resources for growth

Question 35

why is DNA/introns compared when finding out how closely related 2 organisms are?

Answer 35

humans have more introns than exons

introns are compared to find a DNA fingerprint to see how closely related 2 people are

Question 36

what caused the exponential growth of the human population?

Answer 36

better farming techniques can provide food for a larger population
better standards of living
medical care
immunisation programmes
medical discoveries

Question 37

how to calculate percentage population growth?

Answer 37

population change during time period/ population at stat of period X 100