7 Genetics: 18 Populations and Evolution

Question 1

What can species exist as?

Answer 1

One or more populations.

Question 2

What is the definition of a population?

Answer 2

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

Question 3

What is the definition of a gene pool?

Answer 3

The complete range of alleles present in a population.

Question 4

What is allele frequency?

Answer 4

How often an allele occurs in a population.

Question 5

What does the Hardy-Weinberg principle predict?

Answer 5

Allele frequencies will not change from generation to generation.

Question 6

Under what conditions does the Hardy-Weinberg principle apply?

Answer 6

• large population
• no immigration or emigration
• no mutations
• no natural selection
• random mating

Question 7

What can be calculated using the Hardy-Weinberg equations?

Answer 7

The frequency of alleles, genotypes, and phenotypes within popultions.

Question 8

What are the Hardy-Weinberg equations?

What do the variables stand for?

Answer 8

p^2 + 2pq + q^2 = 1
p + q = 1

p - frequency of dominant allele
p^2 - frequency of homozygous dominant genotype

q - frequency of recessive allele
q^2 - frequency of homozygous recessive allele

2pq - frequency of heterozygous genotype

Question 9

What can individuals within a population show?

Answer 9

A wide range of variation in phenotype.

Question 10

What is variation in phenotype due to?

Answer 10

Genetic and environmental factors.

Question 11

What is the primary source of genetic variation?

Answer 11

Mutation.

Question 12

What produces further genetic variation?

Answer 12

Meiosis and the random fertilisation of gametes during sexual reproduction.

Question 13

What is natural selection caused by?

Answer 13

Predation, disease, and competition for the means of survival result in differential survival and reproduction.

Question 14

What is the basis of natural selection?

Answer 14

Organisms with phenotypes providing selective advantages are likely to produce more offspring and pass on their favourable alleles to the next generation.

Question 15

What is the effect of differential reproductive success (natural selection) on the allele frequencies within a gene pool?

Answer 15

The frequency of beneficial alleles in the gene pool increases from generation to generation.

Question 16

What is stabilising selection and its effect?

Answer 16

Individuals with alleles for characteristics towards the mean of the range are more likely to survive and reproduce.

Occurs when the environment isn’t changing.

Reduces the range of possible phenotypes.

Allele frequency for average characteristic increases.

Question 17

What is directional selection and its effect?

Answer 17

Individuals with alleles for a single extreme phenotype are more likely to survive and reproduce.

In response to an environmental change.

Allele frequency for extreme characteristic increases.

Question 18

What is disruptive selection and its effect?

Answer 18

Individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce.

Characteristics towards the middle of the range are lost.

Occurs when the environment favours more than one phenotype.

Allele frequencies for both extreme characteristics increases.

Question 19

What is evolution?

In terms of alleles.

Answer 19

A change in the allele frequencies in a population.

Question 20

What can reproductive seperation of two populations result in?

Answer 20

The accumulation of difference in their gene pools.

Question 21

How do new species arise?

Answer 21

When the genetic differences between two populations lead to an inability to interbreed and produce fertile offspring.

Question 22

What is the process of allopatric speciation?

Answer 22

1. Populations that are geographically isolated will experience different selection pressures/ environmental conditions.
2. Different alleles will be more advantageous and so will increase in frequency.
3. The changes in allele frequency will lead to differences accumulating in the gene pools.
4. Eventually, the genetic differences will lead to an inability for members of the populations to interbreed and produce fertile offspring.
5. The populations have become different species.

Question 23

What is the process of sympatric speciation?

Answer 23

1. Populations become reproductively isolated.
2. The two groups can’t interbreed and produce fertile offspring.
3. They become two different species.

Question 24

What are the causes of reproductive isolation?

Answer 24

Random mutations.
Seasonal - individuals within the same population develop different flowering/ mating seasons.
Mechanical - changes in genitalia prevent successful mating.
Behavioural - a group of individuals develop courtship rituals that aren’t attractive to the main population.

Question 25

What does genetic drift do?

Answer 25

It causes changes in allele frequency in small populations.
Could lead to reproductive isolation and speciation.

Question 26

What is genetic drift?

Answer 26

When chance dictates which individuals survive, breed, and pass on their alleles.
(e.g. by chance, one allele for one genotype is passed on to offspring more often than others)

Question 27

Why is genetic drift only important in small populations?

Answer 27

Chance has a greater effect in small populations.
Chance variations in allele frequency tends to even out in large populations.

Question 28

How has evolutionary change over a long period of time resulted in a great diversity of species?

Answer 28

The original population of organisms divided and evolved into separate species. This process has been repeated over a long period to create millions of new species.