Selection

Front 1

Why aren't all alleles equally likely to be passed on?

Back 1

Some organisms may have characteristics that improve their chances of survival

Front 2

What can affect the allelic frequency?

Back 2

Success of reproduction of individuals

Front 3

Describe the process of natural selection

Back 3

All organisms produce more offspring that can be supported by resources such as food and space etc

Even though there's loads of offspring populations can stay the same

Intraspecific competition between organisms of the same species to survive

There is a gene pool within this species

Some will have certain alleles that can help them survive

Those that have these alleles are more likely to produce more offspring

So alleles with the most competitive advantage are most likely to be passed on

Over a long period of time those organisms that have the advantageous allele will increase

Front 4

What makes an allele advantageous?

Back 4

Depends upon environmental conditions

Front 5

What are the 3 different types of selection?

Back 5

Directional, stabilising and disruptive

Front 6

When does directional selection occur?

Back 6

There has been a change in the environmental conditions

Front 7

When does stabilising selection occur?

Back 7

Environmental conditions have remained the same

Front 8

What type of selection favours certain individuals that vary in one direction of the mean?

Back 8

Directional

Front 9

What type of selection favours average individuals closer to the mean?

Back 9

Stabilising

Front 10

Lake Malawi in East Africa contains around 400 different species of cichlids which are small, brightly coloured fish. All these species have evolved from a common ancestor.

Describe one way in which scientists could find out whether cichlids from two different populations belong to the same species

Back 10

See if they can interbreed and produce fertile offspring if they can then same species

Front 11

In a investigation, the tolerance to copper ions of the grass Agrostia tenuis was determined. Samples were taken of plants growing in waste from a copper mine and from nearby areas just outside the mine. The mean copper tolerance of plants from the mine waste was found to be four times higher than that of plants in the surrounding area.

Explain how natural selection could produce a copper -tolerant population in the mine waste

Back 11

Variation present in original population

Copper tolerant individuals more likely to survive

There reproduce and pass on genes to next generation/offspring

Increase in frequency of copper tolerance alleles

Front 12

Explain how emigration / immigration is important in maintaining genetic variability in lemmings populations which have large fluctuations in size

Back 12

Smaller populations have fewer different alleles

Smaller gene pool

Migrants bring in new alleles and increase gene pool

Front 13

A large ocean bay in Northern Canada was formed by melting of glaciers. One species of lemmings inhabits the eastern side and other species of lemming inhabits the western side. Before the glaciers melted there was only one species of lemming present . Explain how two species of lemming evolved from the original species

Back 13

Geographical isolation of populations

Variations present in populations

Different environmental conditions

Different selection pressures

Change in allele Frequency and gene pool

Two populations so unable to interbreed to produce fertile offspring

Front 14

What type of natural selection took place of both species after they had colonised island 3? Explain your answer (3)

Back 14

Directional selection

Selection for one extreme

Whole distribution is shifted towards favoured extreme

Front 15

Some antibiotics bind with specific receptors in the plasma membranes of bacteria. The structure of these receptors is determined genetically. Bacteria can become resident to an antibiotic because a gene mutation results in altered receptor.

Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium.

Back 15

Frequent use of antibiotics creates selection pressure as antibiotic kills bacteria

Bacteria with mutation have selective advantage over others

They survive and reproduce other types

Pass on advantageous allele

Frequency you of advantageous allele increases in next generations

Frequency of resistant types increase in next generations

Front 16

Define selection

Back 16

Process by which organisms what are better adapted to their environment survive and breed, while those less well adapted fail to do so

Front 17

Describe the difference between stabilising and directional selection

Back 17

Stabilising - individuals with alleles for a characteristic towards the middle of the range are more likely to survive, reproduce and pass on their alleles

Directional - individuals with alleles for a characteristics at the extreme end of the range are more likely to survive, reproduce and pass on their alleles