12.4 Selection

Question 1

an organism’s characteristics (phenotype) is determined by…

Answer 1

the genotype (all the alleles an organism has) and its interaction with the environment

Question 2

an allele is…

Answer 2

a different version of the same gene

Question 3

genetic diversity (gene pool) definition

Answer 3

the number of different alleles of genes in a population

Question 4

mutations introduce…

Answer 4

new alleles to populations

Question 5

any mutation could provide a…

Answer 5

• selective advantage
• neutral (does nothing)
• selective disadvantage

Question 6

natural selection definition

Answer 6

process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population

Question 7

what are the means of survival

Answer 7

predation, disease and competition

Question 8

what do the means of survival result in

Answer 8

differential survival and reproductive success (natural selection)

Question 9

variation exists…

Answer 9

within a population (caused by mutation)

Question 10

better adapted individuals are…

Answer 10

more likely to survive and reproduce (differential reproductive success)

Question 11

increased survival chance =

Answer 11

increased reproductive success

Question 12

better adapted organisms are…

Answer 12

more likely to pass on their alleles

Question 13

less well adapted organisms are…

Answer 13

less likely to pass on their alleles

Question 14

organisms are therefore subject to…

Answer 14

selection pressure due to the environment they live in (must always mention what the selection pressure is in the environment)

Question 15

selection pressures determine…

Answer 15

the spread of an allele within the gene pool

Question 16

selection pressures can be either…

Answer 16

Biotic or abiotic

Question 17

examples of biotic factors

Answer 17

• number of predators
• number of prey available
• pathogens
• number of mates
• lack of food availability

Question 18

examples of abiotic factors

Answer 18

• pH of water / soil
• temperature / frost / flooding
• humidity
• light intensity
• salinity of water (salt concentration)

Question 19

how is a new allele made

Answer 19

through mutation of DNA sequence

Question 20

why is there a wide range of variation within a population

Answer 20

due to mutation of genes

Question 21

example of normal distribution in a population

Answer 21

• norm distribution of fur colour in wild mice
• mice have different alleles causing a variation in their phenotype showing fur colours ranging from light to dark in the population
• environment changes which effects how well the mice is camouflaged when hiding from predators

Question 22

3 types of selection

Answer 22

• stabilising selection
• directional selection
• disruptive selection

Question 23

stabilising selection example where the environment of the mice is flushed with soil and mud. how would this effect the mice population

Answer 23

• selection against both extremes (light and dark fur).
• only mean phenotype will have reproductive success (brown mice)
• alleles for mean phenotype are passed on to future generations in greater numbers.
• over time frequency of mean alleles coding for mean phenotypes increases
• alleles coding for both extreme phenotypes decrease

Question 24

directional selection example where the environment changes to dark ash following a recent eruption. how would this effect the mice population

Answer 24

• selection for only 1 extreme (darker fur)
• individuals with advantageous allele have increased reproductive success (mice with darker fur)
• alleles for 1 extreme are passed onto future generations in greater numbers
• over time, frequency of this extreme allele, coding for extreme phenotype (darker fur) increases
• alleles coding for the other extreme phenotype decreases within the population (light fur)

Question 25

evolution by natural selection is a change in the…

Answer 25

allelic frequencies within the population

Question 26

explain how selection occurs in living organisms

Answer 26

1 [names example] variation due to mutation
2 different environmental / abiotic / biotic conditions / selection pressures
3 selection for different advantageous, features / characteristics / mutation / allele
4 differential reproductive success / (selected) organisms survive and reproduce
5 leads to a change in allelic frequency
6 occurs over a long period of time

Question 27

examples of selection from the spec with type of selection

Answer 27

1 birth weight in humans - stabilising
2 antibiotic resistance in bacteria - directional

Question 28

stages of selection - birth weight in humans - stabilising

Answer 28

1 selection against both extremes, low birthweight and high birthweight
2 the mean phenotype of medium birthweight is more likely to survive and reproduce successfully
3 alleles for medium phenotype are passed onto future generations in greater numbers
4 overtime, frequency of the allele coding for medium birthweight increases
5 alleles for both extreme phenotypes, high and low birthweight, decreases

Question 29

stages of selection - antibiotic resistance in bacteria - directional

Answer 29

1 variation due to mutation to create new advantageous alleles that give antibiotic resistance
2 selection for advantageous phenotype of antibiotic resistance and against non-resistant bacteria if antibiotics are taken
3 antibiotic resistant bacteria are more likely to survive and reproduce
4 alleles for antibiotic resistance is passed onto future generations
5 overtime, the frequency of the allele coding for antibiotic resistance increases
6 increase in antibiotic resistant bacteria in the population

Question 30

stages of directional selection - formation of antibiotic resistance in bacteria

Answer 30

1 mutation in bacterial cells change in the DNA base sequence forms a new allele for a protein that blocks affect of the antibiotic
2 selection pressure is the presence of specific antibiotics in culture medium
3 selection for (the advantageous allele) is the bacteria that isnt killed by this antibiotic
4 differential reproductive success is the bacteria that have the beneficial / mutant allele that can still replicate by binary fission
5 allelic frequency is the beneficial / mutant allele increases over time
6 consequence is antibiotic resistance is these bacteria means this antibiotic is now ineffective
7 antibiotic has no effect on human cells as this antibiotic only blocks bacteria from replicating; human cells have different proteins that are not affected by this specific antibiotic