18 Populations And Evolution

Question 1

What is a population

Answer 1

A group of organisms of the same species that occupies a particular space at a particular time and that can potentially interbreed

Question 2

Allelic frequency

Answer 2

The number of times an allele occurs within the gene pool is referred to as the allelic frequency

Question 3

What is the Hardy-Weinberg principle?

Answer 3

Provides a mathematical equation that can calculate the frequency of alleles of a particular gene in a population

Question 4

Five conditions for hardy Weinberg principle

Answer 4

No mutations arise.
The population is isolated, so no flow of alleles into or out of population.
There is no selection so alleles all equally likely to be passed to next generation.
Population is large.
Mating within population is random.

Question 5

Hardy Weinberg two equations

Answer 5

See card 1

Question 6

How to calculate Hardy Weinberg

Answer 6

See card 2

Question 7

Genetic variation arises as a result of

Answer 7

Mutations, sudden changes to genes and chromosomes can be passed on to next generation, main source of variation.
Meiosis, produces new combo of alleles before passed into gametes.
Random fertilisation of gametes, in sexual reproduction this produces new combo of alleles, which gametes fuses with which at fert is random

Question 8

Environmental influences:

Answer 8

Climatic conditions ( temperature, rainfall, sunlight), soil conditions, pH, and food availability

Question 9

When characteristics of organisms grade into one another forming a continuum, what is this controlled by

Answer 9

This type of variation controlled by many genes, polygenes

Question 10

Bell shaped curve used

Answer 10

Normal distribution curve

Question 11

Selection pressures

Answer 11

Environmental factors that limit the population of a species.
These include predation, disease and competition

Question 12

Process of evolution by means of natural selection depends on…

Answer 12

Organisms produce more offspring than can be supported by available supply.
There is genetic variety within the populations of all species.
A variety of phenotypes that selection operates against.

Question 13

Why do species not increase in size exponentially

Answer 13

High death rate.
High reproductive rates evolved in many species to ensure sufficiently large population survives to breed, compensates for high death rates from predation, competition for food, extremes of temp, natural disasters

Question 14

Intraspecific competition involvement in natural selection

Answer 14

Those individ in population best suited to prevailing conditions more likely to survive than those less well adapted.
These individ more likely to breed and pass on favourable allele combos to next generation, which therefore have different allele frequency from previous one.
The pop will have evolved a combo of alleles that is better adapted to prevailing conditions

Question 15

What is important in survival of species

Answer 15

Wide range of genetically different (and therefor phenotypes) in pop.
Larger pop and more genetically varied, greater chance one of more individuals will hav combo of alleles which lead to advantageous phenotype.

Question 16

Three main types of selection

Answer 16

Stabilising selection,
Directional selection,
Disruptive selection

Question 17

Stabilising selection

Answer 17

Preserves avg phenotype of pop by favouring avg individ, selection against extreme phenotypes, e.g. fur length

Question 18

Directional selection

Answer 18

Favours phenotypes that vary in one direction from mean of pop, selection for one extreme phenotype, there will be selection pressure favouring certain combo of alleles, e.g. antibiotic resistance

Question 19

Disruptive selection

Answer 19

Favours individ with extreme phenotypes rather than those with phenotypes around the mean of the pop e.g. large and small males of some animals, small can sneak up on females, large are fierce competitors

Question 20

Polymorphism

Answer 20

Species that have two or more distinct forms that are genetically distinct but exist within same interbreeding population.

Question 21

Environmental factors do not affect probability of particular mutant allele arising, they affect

Answer 21

The frequency of a mutant allele that is already present in the gene pool

Question 22

Evolution by natural selection is a change

Answer 22

In the allelic frequencies within a population.

Question 23

Speciation is the

Answer 23

Evolution of a new species from an existing one.

Question 24

Members of species separated from one another called

Answer 24

Reproductively separated

Question 25

Most important way in which new species are formed is through

Answer 25

Reproductive separation followed by genetic change due to natural selection.

Question 26

Why do different species evolve from the same original species

Answer 26

Separation.
Different mutations, so genetically different.
Each pop experiences different selection pressures, because environ of each slightly different.
Natural selection leads to changes in allelic frequencies of each pop.
Different phenotypes each combo of alleles produces subjected to selection pressure and will lead to pop adapted to its local environ known as adaptive radiation, and results in changes to allele frequencies.
Each pop different species with own gene pool.

Question 27

Genetic drift

Answer 27

Can take place in small populations. Because few members of small population possess smaller variety of alleles than members of large population. Genetic diversity is less and as these few individ breed, genetic diversity of pop is restricted to those few alleles. Those passed on will quickly affect whole pop as their freq is high. Any mutation to one of these alleles that is selectively favoured will also more quickly affect the whole pop because its freq will be high. Effect of genetic drift greater, more likely to develop into separate species. In large pop effect of mutant allele dilute because freq far less in much larger gene pool.

Question 28

Allopathic speciation

Answer 28

Describes the form of speciation where two populations become geographically separated.
May be result of physical barrier eg. Oceans, rivers, mountain ranges and deserts.
If environmental conditions either side of the barrier vary, then natural selection will influence the two pop differently and each will evolve, may result in reproductive separation and so formation of separate species.

Question 29

Sympatric speciation

Answer 29

Describes form of speciation that results within population in the same area leading to them becoming reproductively separated