Mechanisms Of Change

Question 1

What is a gene pool

Answer 1

The sum of genes in a population at a particular time

Question 2

What is the allele frequency

Answer 2

Proportion of particular allele in a population at a particular time

Question 3

What is the definition of genome

Answer 3

All the DNA of an individual

Question 4

What is the definition of Hardy-Weinberg equilibrium

Answer 4

Amount of genetic variation in population will remain constant from one generation to the next in the absence of disturbing factors

Question 5

What is the Hardy-Weinberg equation for allele frequency

Answer 5

p + q = 1

Where p is the dominant and q is the recessive

Question 6

What is the Hardy-Weinberg equation for genotype frequency

Answer 6

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

p^2 = AA, 2pq = Aa, q^2 = aa

Question 7

Why is a population genetically variable

Answer 7

Mutation
Meiosis
Sexual reproduction

Question 8

Why do meiosis and sexual reproduction cause genetic variation

Answer 8

Independent assortment
Crossing over
Random process

Question 9

What is variability persevered by

Answer 9

Diploidy

Heterozygotes shelter rare recessive alleles

Question 10

Describe a population bottleneck

Answer 10

Event drastically reduces the size of a population
Decrease in gene pool so many alleles lost
Low level of genetic diversity
Face higher level of genetic drift

Question 11

Describe genetic drift

Answer 11

Random fluctuations of gene variants
Alleles increase and decrease by chance over time
Continues until allele lost of only one allele present
Decrease in genetic diversity
Can cause new population to be genetically distinct from original

Question 12

Describe the conditions for Hardy-Weinberg equilibrium (5)

Answer 12

Large breeding population 
Random mating
No change in allergic frequency due to mutation 
No immigration or emigration
No natural selection

Question 13

What are the problems with the Hardy-Weinberg equilibrium

Answer 13

Describes ideal state

Disruptive forces commonly occur in nature and this equilibrium rarely applies in reality

Question 14

What is a point mutation

Answer 14

Mutation that affects one base

Substitution or deletion of a single base

Question 15

Describe substitution mutation

Answer 15

One base replaced by another

May mean diff polypeptide

Question 16

Describe deletion mutation

Answer 16

One base deleted
So all triplets altered
Frame shift
Protein may be shortened if stop codon produced earlier

Question 17

What causes chromosome mutation

Answer 17

Chromosomes fail to separate during meiosis

Question 18

Describe aneuploidy

Answer 18

One chromosome only fails to separate

Eg Down’s syndrome and turners syndrome

Question 19

Describe polyploidy

Answer 19

Whole set of chromosomes fail to separate

Individual has 3+ sets of chromosomes rather than 2

Question 20

Describe how mutagens cause mutation

Answer 20

Chemicals which react with bases and changes their characteristics thus causing them to pair wrongly
May be incorporated into DNA
May take place of base
May slip between nucleotides

Question 21

How can radiation cause mutation

Answer 21

Can damage DNA

Alter base structure or backbone

Question 22

Describe selection

Answer 22

Process operating on genetic variation in a population

Leads to the differential perpetuation of alleles to subsequent generations involving both survival and reproduction

Question 23

Describe survival of the fittest

Answer 23

Alleles that are better adapted survive and reproduce more successfully

Question 24

What is meant by the phrase struggle for existence

Answer 24

Competition for resources

Question 25

What is meant by an organisms “fitness”

Answer 25

Measure if features that allow the organism to be adapted to its environment

Question 26

What are the key points if selection (6)

Answer 26

Acts on a population
Environmentally dependent
Basis of variation must be genetic
Edits genetically inheritable features
Selection favours fittest
Differential reproductive success - better adapted more likely to survive

Question 27

Describe stabilising selection

Answer 27

Environmental conditions largely unchanging
Acts against extremes
Does not lead to evolution
Maintains adaptive norm

Question 28

Draw the graphical change in stabilising selection

Answer 28

See notes

Question 29

Describe directional selection

Answer 29

Changing environment conditions
Some extremes have a selective advantage
They survive and reproduce
Change in genetic composition of population
Leads to evolution

Question 30

Draw the graphical change for directional selection

Answer 30

See notes

Question 31

What does polymorphism mean

Answer 31

Presence of 2 or more distinct forms in a population

Question 32

What is apostatic selection

Answer 32

Different forms maintained

Predator hunts most common

Question 33

What does speciation mean

Answer 33

Evolution of a new species from ancestral species

Question 34

What is a species

Answer 34

Group of organisms which can interbreed to produce fertile offspring
They are reproductively isolated from other species

Question 35

What is allopatric speciation

Answer 35

Evolution of a new species

Due to geographical isolation

Question 36

Describe the process of allopatric speciation

Answer 36

1. Ancestral species expands to new locations
   Regular gene flow in gene pool
2. Physical barrier isolates populations geographically
   Gene flow with ancestral population prevented
3. 2 populations subject to different selection pressures
4. 2 populations diverge genetically
   If still capable of interbreeding then it is not a new species
   Of they can no longer interbreed then a new species has evolved

Question 37

What happens during interspecific competition

Answer 37

One species eliminates the other
Or
Both evolve further so there is niche divergence