Types of Selection

Question 1

What are the environmental factors that limit a population called?

Answer 1

Selection pressures.

Question 2

Give 3 examples of selection pressures.

Answer 2

Predation, disease, competition.

Question 3

What is a gene pool?

Answer 3

The total number of all alleles of all genes of all individuals within a particular area at a given time.

Question 4

What is natural selection?

Answer 4

Individuals with advantageous genes for survival live and reproduce with each other. This means that offspring produced will have desirable traits and survive. Weaker animals with less desirable traits die out, so these alleles are removed from the gene pool.

Question 5

What 2 things are populations with little genetic variation more vulnerable to?

Answer 5

Disease and climate change.

Question 6

Why are larger populations more likely to survive?

Answer 6

They have a larger gene pool, meaning that they are more varied. This means a variety of genes can be passed on to suit whatever condition the organism lives in

Question 7

For example, if a food source is limited, how will this affect population size?

Answer 7

Limited food means organisms who that do not contain the ‘best’ alleles to help with competing die out, so population decreases.

Question 8

Name 3 types of selection (not natural).

Answer 8

Stabilising
Disruptive
Directional

Question 9

Define stabilising selection.

Answer 9

A type of selection that keeps allele frequency relatively constant over several generations.

Question 10

What type of characteristics will stabilising selection eliminate?
Use the example of birth weights.

Answer 10

Extremes. For example very high or very low birth weights are selected against, leading to the average birth weight being the most common.

Question 11

Describe the shape of a graph that represents stabilising selection.

Answer 11

A bell shaped curve, where the extremes on both ends are very low.

Question 12

For stabilising selection, if the environmental conditions were to fluctuate, how does this impact survival of the species?

Answer 12

If the environment were to change and match extremes, this means that organisms with extreme alleles are adapted for survival.

Question 13

For organisms with extreme alleles, using stabilising selection, how are they selected against?

Answer 13

When environmental conditions are constant, organisms with the allele to match these ‘average’ conditions reproduce with each other. This is because organisms with extreme alleles die out as they are not adapted to survive this condition.

Question 14

Define directional selection?

Answer 14

A type of natural selection that produces a gradual change in allele frequencies over several generations.

Question 15

Why does directional selection happen?

Answer 15

There may be a change in the environment or a new allele that appears in the population that is advantageous.

Question 16

On a graph, which side would directional phenotypes favour?

Answer 16

It favours one extreme phenotype on one side of the mean.

Question 17

Describe how directional selection happens over time.

Answer 17

Organisms that adapt to a new environmental conditions, such as higher temperature, survive, reproduce and pass on their alleles adapted to this condition onto offspring. Over generations, this allele becomes more prominent in the population.

Question 17

What does disruptive selection do to 2 different types of alleles?

Answer 17

Maintains high frequencies of both of the different ones.

Question 18

Which alleles does disruptive selection favour?

Answer 18

Extreme phenotypes at the expense of the intermediate phenotypes.

Question 19

What is polymorphism and how does disruptive selection lead to it?

Answer 19

It is the continued existence of 2 or more distinct phenotypes in a species.
Disruptive selection leads to this by making the extreme phenotypes most prominent in a population

Question 20

How can humanity act as a selection pressure?
Use the example of antibiotic resistance.

Answer 20

Man made things can change the alleles of species which increases their chances of survival.
For example, bacteria are becoming resistant to antibiotics because they are developing new alleles that enables that enables them to survive the new conditions.

Question 21

What is artificial selection?

Answer 21

Where farmers choose which animals breed together so offspring with desired traits can be produced.

Question 22

Why do farmers use artificial selection?

Answer 22

It can lead to high yields.

Question 23

Give a drawback of artificial selection.
This drawback can lead to increased risk of disease.

Answer 23

It can lead to inbreeding, which causes reduced genetic diversity. This can increase the risk of disease.