2.2 a) Evolution - Drift and Selection

Question 1

What is evolution?

Answer 1

Evolution is the change over time in the proportion of individuals in a population differing in one or more inherited traits

Question 2

During evolution, changes in ___ ___ occur through random and non-random processes.

Answer 2

allele frequency

Question 3

Name the random and non-random processes which change the frequency of alleles during evolution.

Answer 3

random: genetic drift
non-random: natural selection and sexual selection.

Question 4

What does natural selection act on?

Answer 4

genetic variation in populations

Question 5

Variation in traits arises as a result of ___.

Answer 5

mutations

Question 6

Mutations are the original source of…

Answer 6

New DNA sequences

Question 7

New sequences of DNA that are a result of mutations can be ___ ___.

Answer 7

novel alleles

Question 8

What are novel alleles?

Answer 8

alleles that are new to a population and arise through mutations

Question 9

Most mutations are ___ or ___, but some are…

Answer 9

harmful or neutral, beneficial to the fitness of an individual

Question 10

When discussing natural selection, what is the first thing you should mention?

Answer 10

organisms produce more offspring than the environment can support

Question 11

What is natural selection?

Answer 11

when individuals with variation which makes them better suited to their environment tend to survive longer, allowing them to pass on their beneficial alleles to the next generation

Question 12

Natural selection results in…

Answer 12

the non-random decrease in deleterious alleles and increase in beneficial alleles

Question 13

What is sexual selection?

Answer 13

the non-random processes involving the selection of alleles which increase an individual’s chances of mating and producing offspring (survival of the hottest)

Question 14

What may sexual selection lead to?

Answer 14

sexual dimorphism

Question 15

What is sexual dimorphism?

Answer 15

when males and females of the same species look different

Question 16

Sexual selection can be down to… or…

Answer 16

male-male rivalry or female choice

Question 17

What is male-male rivalry?

Answer 17

when males fight for access to females. large size or weaponry increases access to females

Question 18

What is female choice?

Answer 18

when females assess the fitness of males for mating

Question 19

What is genetic drift?

Answer 19

genetic drift is when chance events cause unpredictable fluctuations in allele frequencies

Question 20

Genetic drift is more important in ___ ___ as alleles are more likely to be…

Answer 20

small populations, lost from the gene pool.

Question 21

Which two effects involve genetic drift?

Answer 21

the bottleneck effect
the founder effect

Question 22

What is a population bottleneck? (aka the bottleneck effect)

Answer 22

when the size of a population is reduced for at least one generation. alleles may be lost

Question 23

Describe the founder effect.

Answer 23

The founder effect is when a few individuals are isolated from the larger population (eg by flying to an island). These few members breed and create a new population with a gene pool that does not represent the original population

Question 24

How does genetic drift alter gene pools?

Answer 24

it changes the frequency of different alleles (by reducing/removing the some alleles, the frequency of all alleles changes)

Question 25

As a result of genetic drift, some alleles may be ___ or ___ represented.

Answer 25

over or under

Question 26

When selection pressures are strong, the…

Answer 26

rate of evolution can be rapid

Question 27

What are selection pressures?

Answer 27

the environmental factors that influence which individuals in a population pass on their genes

Question 28

Selection pressures can be ___ or ___.

Answer 28

biotic or abiotic

Question 29

Name four biotic selection pressures.

Answer 29

competition, predation, disease, parasitism

Question 30

Name five abiotic selection pressures.

Answer 30

temperature, light intensity, pH, humidity, salinity

Question 31

What does the Hardy-Weinberg (HW) principle state?

Answer 31

in absence of evolutionary influences, the allele and genotype frequencies in a population will remain constant over generations

Question 32

What are the five conditions for maintaining the HW equilibrium?
(aka what must we assume in order for the HW principle to work?)

Answer 32

1. there is no gene flow (through immigration or emigration)
2. no natural selection
3. mating is random
4. no mutations
5. the population is large

Question 33

What can the HW principle be used to determine?

Answer 33

whether or not a change in allele frequency is occurring over time

Question 34

HW can be used to calculate ___, ___ and ___ frequency in a population.

Answer 34

allele, phenotype and genotype

Question 35

What is the HW equation?
What other equation can you not live without?

Answer 35

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

p + q = 1.

Question 36

What do p and q represent in the HW equation?

Answer 36

the frequency of the dominant (p) and recessive (q) allele

Question 37

What does p^2, 2pq and q^2 represent in the HW equation?

Answer 37

p^2 = frequency of the homozygous dominant genotype
2pq = frequency of the heterozygous genotype
q^2 = frequency of the homozygous recessive genotype

Question 38

How do you answer HW questions?

Answer 38

1. FInd the frequency of whatever allele/genotype they’re telling u about (x), by doing x / total population.
2. If they are asking about genotype, then x/total population will equal p^2. If they are asking about allele frequency, then x/total population would equal p. Assume they will ask about the frequency of either of the homozygous genotypes (dominant or recessive). If they do, then find p by taking the square root of p^2
3. Once you have found p, use the equation ‘p + q = 1’ to find the frequency of the other allele (q).
4. sub in the values of p and q to the equation ‘p^2 + 2pq + q^2 = 1’. It should equal one
5. assuming ‘p^2 + 2pq + q^2 = 1’ is true, then you can find the frequency of whichever of the 3 genotypes they’re asking about.

Question 39

Natural selection is when individuals with ___ which makes them better suited to their ___ tend to survive ___, allowing them to pass on their ___ ___ to the next generation

Answer 39

variation, environment, longer, beneficial alleles

Question 40

Evolution is the change over time in the ___ of ___ in a population differing in one or more ___ traits.

Answer 40

proportion, individuals, inherited

Question 41

Selection pressures are ___ factors that influence which ___ in a population pass on their ___.

Answer 41

environmental, individuals, genes

Question 42

The HW principle States that, in absence of ___ influences, the ___ and ___ frequencies in a population will remain constant over ___.

Answer 42

evolutionary, allele, genotype, generations

Question 43

2022 P2 Q9.a):
Explain why genetic drift is likely to have occurred in the gene pool of Big Mountain Rockhorn sheep

Answer 43

Genetic bottleneck/founder effect
(1)
(causing) unpredictable/random changes in allele frequencies/gene pool.
OR
alleles lost/misrepresented/overrepresented/under-represented. (1)

*sometimes all they want is a definition, and you don’t have to link it to anything in the question