18.Populations And Evolution

Question 1

What is a population

Answer 1

Group of organisms of same species that occupy a particular space at particular time and ca potentially interbreed

Question 2

What is gene pool

Answer 2

All alleles of all genes of all individuals in a population at a given time

Question 3

What is allelic frequency

Answer 3

Number of time the allele occurs within the gene pool

Question 4

What assumptions are made when using hardy Weinberg

Answer 4

No mutations arise
Population is isolated, no flow into or out
No selection, all alleles likely to be passsed on
Population is large
Mating is random

Question 5

What are the equations of Hardy Weinberg

When A (dominant) = p

Answer 5

P+q=1.0

P^2 + 2pq + q^2 = 1.0

Question 6

What are genetic variations due to

Answer 6

Mutations - sudden changes to genes or chromosomes
Meiosis - nucleic division of gametes, new combinations of alleles
Random fertilisation of gametes - sexual reproduction, new combo of alleles, random fertilisation of gametes

Question 7

How does environmental influence variation

Answer 7

Exerts influence on way the organisms genes are expressed, determines where organisms lie on continuum

Question 8

What does process of evolution by natural selection depend upon

Answer 8

• organisms producing more offspring than can be supported by the available supply of food light space
• there’s genetic variation within population of all species
• variety of phenotypes that selection operates against

Question 9

What is role of over production of offspring in natural selection

Answer 9

Populations have evolved high reproductive rates in order to ensure sufficiently large amount of population survives to breed and produce next generation, to compensate for high death rates by predation, food comp, natural disasters

Question 10

What’s the link between over production and natural selection

Answer 10

When there’s too many offspring for available resources, there’s competition amongst individuals (intraspecific) for limited resources, the greater the numbers the greater the competition, the more individuals die in struggle to survive

Question 11

What’s role of variation in natural selection

Answer 11

• Larger population
• more genetically varied the individuals
• greater chance that one or more possess combo of alleles that lead to advantageous phenotype
• more likely to breed and pass on allele combinations
• survival will favour those with advantageous alleles

Question 12

What are the 3 types of selection

Answer 12

Stabilising selection
Directional selection
Disruptive selection

Question 13

What is stabilising selection

Answer 13

Preserves average phenotype of population by favouring average individuals, favour against the extremes

Question 14

What is directional selection

Answer 14

Changes phenotypes of population favouring phenotypes that vary in one direction from mean of population, selection for extreme phenotypes

Question 15

What is disruptive selection

Answer 15

Favours individuals with extreme phenotypes rather than those the phenotypes around the mean of population.

Question 16

What is speciation

Answer 16

Evolution of new species from existing ones

Question 17

What is allopatric speciation

Answer 17

When two populations become geographically separated, may be physical barrier, if environmental conditions either side of barrier vary, natural selection will influence two populations differently.
Each will evolve differently due to different conditions

Question 18

What’s sympatric speciation

Answer 18

Form of speciation that occurs within a population in same area leading to them becoming reproductively separated

Question 19

What are the 5 forms of isolating mechanisms

Answer 19

Geographical - physical barriers
Ecological - populations inhabit diff habitats in same area, don’t meet
Temporal - breeding seasons don’t coincide
Behavioural - mating mutations that lead to no courting
Mechanical - anatomical differences that prevent mating eg penis can’t fit
Gametic - failure of gametes meeting or biochemical incompatibility
Hybrid sterility - hybrids formed by fusion of two gametes from seater species

Question 20

What are the effects of each form of selection on evolution

Answer 20

Stabilising-reduces number of extreme phenotypes and so little variation in characteristics so no evolution

Directional-favours new optimum phenotype, therefore evolution to a degree

Disruptive-over many years it will form two different species as they evolve to favour two opposite extreme characteristic

Question 21

How does natural selection affect allelic frequency

Answer 21

Selection due to environmental factors, Environmental changes affect probability of allele being passed on in population and hence number of times it occurs in gene pool

Question 22

How do new species form

Answer 22

• Individuals tend to breed within same population but can with other populations
• if one population is separated and undergoes different mutation it will be genetically different
• each populations experience different selection pressures due to different environments
• natural selection leads to change in allelic frequencies
• adaptive radiation-when each populations adapts to local environment
• change in allelic frequencies of each population, each with its one gene pool - different species