Genetic diversity and natural selection

Question 1

What leads to the vast genetic diversity we find on earth?

Answer 1

Differences in DNA

Question 2

How do organisms of the same species differ?

Answer 2

In their combination of alleles

Question 3

What is genetic diversity described as?

Answer 3

The total number of different alleles in a population

Question 4

What is a population?

Answer 4

A group of individuals of the same species that live in the same place and can interbreed

Question 5

How is the genetic diversity of a species increased?

Answer 5

The greater the number of different alleles that all members of a species possess

Question 6

What does a greater genetic diversity mean for the survival of a population?

Answer 6

The more likely that some individuals will survive an environmental change

Question 7

What happens if there is a wider range of alleles in a population?

Answer 7

A greater probability that some individual will possess a characteristic that suits it to the new environmental conditions

Question 8

What is a factor that enables natural selection to occur?

Answer 8

Genetic diversity

Question 9

Why are not all alleles of population equally likely to be passed on?

Answer 9

As only certain individuals are reproductively successful and so pass on their alleles

Question 10

What affects allele frequency in a population?

Answer 10

Differences between the reproductive success of individuals

Question 11

What is found within any population of a species in regards to genes?

Answer 11

A gene pool containing a wide variety of alleles

Question 12

What happens within a gene pool of a population?

Answer 12

Random mutations of alleles

Question 13

What may random mutations of alleles in a gene pool result in?

Answer 13

• A new allele of gene
• In most cases will be harmful
• In certain environments, the new allele might give its possessor an advantage over other individuals

Question 14

What could be the advantages of having a new allele of a gene in a given population?

Answer 14

• Individuals will be better adapted and more likely to survive and obtain available resources
• So have a better chance of breeding successfully and passing on allele to next generation

Question 15

What happens if individuals pass on ‘advantageous’ alleles?

Answer 15

The next generation will have it and are more likely to survive and reproduce

Question 16

What will happen over many generations if a mutation of an allele occurs and it is passed on?

Answer 16

• Number of individuals with the new allele will increase at the expense of the individuals with the less ‘advantageous’ allele
• The frequency of the new allele in the population increases

Question 17

What is selection?

Answer 17

The process by which organisms that are better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to

Question 18

What ware the two ways selection may favour?

Answer 18

• Individuals that vary in one direction from the mean of the population
• Average individuals

Question 19

What is selection that favours individuals in one direction called?

Answer 19

Directional selection

Question 20

What does directional selection do?

Answer 20

Changes characteristics of the population

Question 21

What is selection that favours average individuals called?

Answer 21

Stabilising selection

Question 22

What does stabilising selection do?

Answer 22

Preserves the characteristic of a population

Question 23

What are most characteristics influenced by?

Answer 23

More than one gene - polygene

Question 24

Which characteristics are more influenced by the environment?

Answer 24

Ones determined by polygenes rather than ones determined by single genes

Question 25

What does the effect of the environment on polygenes produce?

Answer 25

Individuals in a population that vary about the mean (when you plot this distribution, you get a normal distribution curve)

Question 26

Which phenotypes will survive if the environmental conditions change?

Answer 26

Ones that are best suited to the new conditions

Question 27

Where on the normal distirbution curve will be the phenotypes that are more likely to survive if the environmental conditions change?

Answer 27

To the left or the right

Question 28

What will happen if the environemental conditions change, and the phenotype is on the left or right of the normal distribution curve?

Answer 28

- More likley to survive and breed - So, will contribute more offspring (and the alleles the offspring possess) to the next generation than other individuals

Question 29

What will happen to the normal distribution curve in directional selection?

Answer 29

Over many generations, the mean will move in the direction of the individuals that are more suited to the new conditions

Question 30

What is an example of directional selection?

Answer 30

Development of antibiotic resistance in bacteria

Question 31

What happened shortly after the discovery of antibiotics?

Answer 31

- Became clear that the effectiveness of some antibitoics at killing bacteria was reduced - Was found that these populations had developed resistance to bacteria

Question 32

What was the resistance due to when the effectiveness of antibiotics in killing bacteria was reduced?

Answer 32

A chance mutation within the bacteria

Question 33

What is an example of antibiotic resistant bacteria(directional selection)?

Answer 33

Resistance to penicillin

Question 34

How did the resistance to penicillin begin in bacteria?

Answer 34

- Spontaneous mutation occured in the allele of a gene in the bacterium - Enabled it to make a new protein that broke down penicillin before it could kill the bacterium

Question 35

What situation did the bacterium that mutated to form resistance to penicillin happen to be in?

Answer 35

- One where penicllin was used as a treatment - In these circumstances, the mutations gave the bacterium an advantage as they used the protein to break down the antibiotic - So, it survived while the rest of the bacteria population were killed by it

Question 36

What happened to the bacterium that survived the penicillin due to its random mutation?

Answer 36

Divided by binary fission to build up a small population of penicillin-resistant bacteria

Question 37

What was the penicillin-reistant bacteria population able to do?

Answer 37

- More able to survive and multiply in the presence of penicillin - Population increased at the expense of non-resistant bacteria - Frequency of the allele that enabled production of protein increased in population

Question 38

What happened to the normal distribution curve of the penicillin-resistant bacteria?

Answer 38

Shifted in direction of a population having a greater resistance to penicillin

Question 39

Do bacteria mutate due to the presence of antibiotics?

Answer 39

No - they occur randomly and rarely

Question 40

What is the total number of mutations like in bacteria?

Answer 40

Large given there are so many bacteria

Question 41

Do all mutations in bacteria have advantages?

Answer 41

- No and most will be harmful, causing some bacterium to die - Very occasionally a mutation will be advantageous and even that depends on the circumstances

Question 42

What will happen with the continued use of antibiotics in terms of bacteria?

Answer 42

Greater chance that the mutant population will out-compete and replace the original population

Question 43

If the environmental conditions remain stable, where on the normal distribution curve will the phenotypes most likely to favoured be?

Answer 43

Closest to the mean

Question 44

What are the individuals closest to the mean in stabilising selection more likely to do?

Answer 44

Pass on their alleles to the next generation

Question 45

Which individuals are less likely to pass on their alleles in stabilsing selection?

Answer 45

Those with phenotypes at the extremes of the normal distribution curve

Question 46

What does stabilsing selection tend to do to the phenotypes at the extremes?

Answer 46

Eliminate them and with it the capacity for evolutionary change

Question 47

What is an example of stabilsing selection?

Answer 47

Human birth weights

Question 48

How is human birth weights an example of stabilsing selection?

Answer 48

- Body mass at birth of babies was found over a 12 year period and infant mortality rate was also recorded - There is a much greater risk of infant death when the birth weight is outside the range of 2.5-4 kg - This is stabilising selection as mortality rate is greater at 2 extremes so the population's characteristics are preserved rather than changed

Question 49

What is disruptive selection?

Answer 49

It favours extreme phenotypes at the expense of intermediate phenotypes

Question 50

When does disruptive selection occur?

Answer 50

When an environmental factor (e.g. temperature) takes two or more distinct forms

Question 51

What is an example of disruptive selection?

Answer 51

If temperature alternated between cold in winter (favouring long fur length) and hot in summer (favouring short fur length)

Question 52

What does the difference in temperature in winter and summer lead to? (fur length on foxes)

Answer 52

Could lead to 2 separate species of the mammal - one with long fur and active in winter, the other wish short fur and active in summer

Question 53

What kind of adaptations can natural selection result in?

Answer 53

- Anatomical (shorter ears and thicker fur in arctic foxes) - Physiological (oxidising of fat rather than carbs in kangaroo rats) - Behavioural (autumn migration of swallows from UK in winter)