7B Populations and evolution

Question 1

What is a species?

Answer 1

Group of similar offspring that can reproduce to give fertile offspring

Question 2

What is a population?

Answer 2

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 the allele frequency?

Answer 4

How often an allele occurs in a population

Question 5

What is the need for the Hardy Weinberg principle?

Answer 5

Mathematical model that predicts the frequencies of alleles in one population wont change from one generation to the next

Question 6

What conditions are needed for hardy Weinberg?

Answer 6

• large pop
• no mutations, no immigration/emigration or natural selection
• random mating

Question 7

What is the equation for allele frequency?

Answer 7

P+Q = 1

p = frequency of dominant allele
q = frequency of recessive allele

Question 8

What is the equation for genotype frequency and how does it help?

Answer 8

P^2 + 2PQ + q^2 = 1

p2 = homozygous dominant genotype
2pq= homozygous genotype
q2 = homoezygous recessive genotype

These genotype frequencies can be used to work out phenotype frequencies if you know how genotype relates to phenotype

Question 9

What is variation?

Answer 9

Differences that exist between individuals

Question 10

How can genetic variation arise?

Answer 10

• meiosis
• crossing over of chromatids
• independent segregation
• random fertilisation of gametes

Question 11

What is evolution?

Answer 11

The frequency of an allele in a pop. changes over time

Question 12

What is natural selection ?

Answer 12

This is where selection pressures (predatation, disease, competition) create a striggle for survival
The variation between individuals mean some are better adapted to others
There is different levels of survival and reproductive success in a population
Those with a phenotype that are most likley to survive will reproduce and pass on their genes
A greater population of the next generation will inherit the beheficial alleles
Frequency of beneficial allele in gene pool increases from generation to generation

Question 13

What are the types of natural selection?

Answer 13

Stabilising - individuals with allelles for characteristics towards the middle of the range are more likely to survive and reproduce and occurs when environment isnt changing eg birth weight

Directional - Alleles for a single extreme phenotype are
more likely to survive and reproduce in repsonse to an environmental change eg speed

Distruptive - Individuals will extreme phenotypes are more likely to survive and reproduce so characteristics towards the middle range are lost

Question 14

What is speciation?

Answer 14

The development of new species from an existing species that occurs when populations of the same species become reproductively isolated ( they can no longer interbreed to produce fertile offspring)

Question 15

What are the 2 types of speciation?

Answer 15

Allopatric
Sympatric

Question 16

What is allopatric speciation?

Answer 16

This is where populations are geographically separated by a physical barrier that can cause each population to experince different selection pressures leading to changes in allele frequency

Question 17

What will allopatric speciation lead to ?

Answer 17

Changes in phenotypic frequencies so that both populations will no longer be bale to breed with one another to produce fertile offspring

Question 18

What is sympatric speciation?

Answer 18

Random mutations within a pop prevent indivisuals carrying the mutation from breeding with each others that dont carry mutation

Question 19

What are the mechanisms of reproductive isolation?

Answer 19

Seasonal changes - flowering seasons, mating seasons
Mechanical changes - changes in size, shape or function of genitalia
Behavioural changes - courtship rituals

Question 20

What is genetic drift?

Answer 20

This is where chance dictates which alleles are passed

Question 21

How does genetic drift work?

Answer 21

1. individuals within a population show variation in their genotypes
2. The allele for one genotype is passed on to more offspring then the others so the number of individuals with the allele increases
3. If by chance the same allele is passed on more often again and again it can lead to evolution as the alleles becomes more common in the population

Question 22

How does genetic drift and population size link?

Answer 22

Genetic drift has a greater effect on smaller populations where chance has a greater influence but in later populations any chance factors tend to even out across the whole population