7.2-3 Populations, Evolution and Selection

Question 1

What is a population?

Answer 1

A group of organisms of the same species

In a particular space at a particular time that can potentially interbreed

Question 2

What is a gene pool?

Answer 2

The total number of alleles present in a population

Question 3

What is allelic frequency?

Answer 3

The proportion if a certain allele in a gene pool

Question 4

What is the Hardy-weinberg equation used for?

Answer 4

To estimate the frequency of alleles in a population

To see whether a change in allelic frequency is occurring

Question 5

What does the Hardy-Weinberg principle predict?

Answer 5

The proportion of dominant and recessive alleles in a population remain constant

From one generation to the next

Question 6

What is assumed in the Hardy-weinberg equation?

Answer 6

No mutations occur
No movement of alleles - population is isolated
Large breeding population
All alleles have an equal chance to be passed on to the next generation (no selection)
Mating is random

Question 7

What are the formulas for the Hardy-weinberg principle?

Answer 7

p + q = 1.0

And

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

Question 8

What do the p’s and q’s represent in the Hardy-weinberg equations?

Answer 8

p = frequency of the dominant allele (eg A)

q = frequency of the recessive allele (eg a)

p^2 = frequency of homozygous dominant (eg AA)

2pq = frequency of heterozygous (eg Aa)

q^2 = frequency of homozygous recessive (eg aa)

Question 9

Why are there variations in alleles of genes?

Answer 9

Random fertilisation
Meiosis
Mutation

Environmental influences

Question 10

What is the niche of a species?

Answer 10

It’s role within the environment

Therefore species with the same niche compete with each other to survive

Question 11

What is the idea of natural selection?

Answer 11

The better adapted species survive

Question 12

What has Darwin suggested about large numbers of offspring?

Answer 12

So there is greater intraspecific competition

So only the best alleles survive, to reproduce and pass on to the next generation

Question 13

What is best in a changing environment?

Answer 13

Variation in genotypes and phenotypes increases the chance a species will survive

Question 14

What do you include in natural selection?

Answer 14

Variation
Mutation 
Environmental change
Competition 
Survival
Reproduction 
Alleles

(Frequency of alleles changing leads to evolution)

Question 15

What is selection?

Answer 15

Choosing the individuals that are better adapted to their environment are more likely to survive and breed

Question 17

What are the types of selection?

Answer 17

Directional
Stabilising
Disruptive

Question 18

What is directional selection?

Answer 18

Selection that favours a phenotype best suited to a changing environment at one extreme of the population

This results in changes to the characteristics of a population as these individuals are more likely to survive and breed - pass on their alleles

The ‘mean’ will therefore shift

Question 19

What is stabilising selection?

Answer 19

Selection against both extremes (eliminating extreme phenotypes) associated with non-changing/stable environments over many years

Those closest to the mean are more likely to pass their alleles on - maintaining favourable characteristics = a successful species

The range and distribution becomes smaller and narrower

Question 20

What is disruptive selection?

Answer 20

Both extremes of the normal distribution are favoured over the mean

Question 21

What is speciation?

Answer 21

New species arise after a population becomes separated and cannot interbreed

Question 22

What are the two type of speciation?

Answer 22

Allopatric - caused by a physical barrier

Sympatric - chromosomal error

Question 23

Describe allopatric speciation?

Answer 23

A population is geographically separated
Genetic variation
Natural selection leads to the frequency of alleles have changed
The two populations are so different they can’t successfully breed

= separate species

Question 24

What is one other way evolution occurs? Who does this greatly affect?

Answer 24

Genetic drift
Chance dictates which alleles are passed on

Greatly affects a small population

Question 25

Describe sympatric speciation?

Answer 25

A species inhabits the same geographical region

But due to a chromosomal error during cell division it could lead to reproductive isolation

Eg mechanically (penis doesn’t fit the vagina)
Or courtship behaviour is no longer recognised