10 - Variation and Evolution (C2)

Question 1

What are the 4 types of selection pressures?

Answer 1

• Environment e.g. drought
• Intraspecific competition e.g. for food
• Interspecific competition e.g. predation
• Human factors e.g. deforestation

Question 2

What are 2 examples of natural selection?

Answer 2

• Camouflage

- Mimicry (e.g. hover flies looking like wasps)

Question 3

What is discontinuous variation?

Answer 3

Characteristics that are clear-cut and controlled by a single gene

Question 4

What is continuous variation?

Answer 4

• Characteristic within a population that shows a gradation from one extreme to another
• Controlled by a number of genes

Question 5

What is the definition of a gene pool?

Answer 5

The total of all alleles for all of the genes in a population

Question 6

What can selection pressures affect?

Answer 6

• The frequency of alleles within the gene pool

- The survival of different phenotypes in a population

Question 7

What does the Hardy-Weinberg equation measure?

Answer 7

Allele frequency

Question 8

What does the Hardy-Weinberg principle state?

Answer 8

That the frequencies of dominant and recessive alleles and genotypes will remain constant if certain conditions remain true

Question 9

What conditions must be true in the Hardy-Weinberg principle?

Answer 9

• Large population
• No selection for or against any phenotype
• Random mating throughout population
• No mutations
• Population is isolated e.g. no immigration or emigration

Question 10

What is the Hardy-Weinberg equation and what do the letters stand for?

Answer 10

p2 + 2pq + q2 = 1
p = frequency of dominant allele
q = frequency of recessive allele
p + q = 1
p2 = frequency of homozygous dominant
2pq = frequency of heterozygous
q2 = frequency of homozygous recessive

Question 11

What can cause speciation?

Answer 11

• Genetic drift in isolated population
• The founder effect of disproportionate allele frequencies in small populations
• Natural selection

Question 12

When does allopatric speciation occur?

Answer 12

When populations occupy different environments

Question 13

When does sympatric speciation occur?

Answer 13

When populations are reproductively isolated within the same environment

Question 14

When does behavioural isolation occur?

Answer 14

When 2 different species or populations evolve courtship displays which are essential for successful mating

Question 15

When does ecological isolation occur?

Answer 15

When 2 species or populations occupy different habitats within the same environment

Question 16

When does geographical isolation occur?

Answer 16

When 2 populations occupy 2 different environments which are separated by some physical barrier

Question 17

When does morphological isolation occur?

Answer 17

When the reproductive structures are physically incompatible

Question 18

When does seasonal isolation occur?

Answer 18

When 2 or more species or populations live within the same area but are reproductively active at different times

Question 19

Why is a mule infertile?

Answer 19

It has 63 chromosomes which is an odd number so they can’t form homologous pairs in prophase 1 of meiosis

Question 20

Why could a male human (46 chromosomes) not breed with a female lion (46 chromosomes)?

Answer 20

They have species specific binding proteins on their sperm and oocyte which don’t correspond

Question 21

What is the bottleneck effect?

Answer 21

Where the population size is dramatically reduced by a catastrophic event

Question 22

What is the founder effect?

Answer 22

Where a small number of individuals colonise a new area

Question 23

What things can change allele frequencies?

Answer 23

• Genetic drift
• Mate selection
• Gene flow
• Natural selection
• Geographical barriers
• Mutations
• Immigration

Question 24

What is variation caused by?

Answer 24

• Mutation
• Random fertilisation of gametes
• Independent assortment of chromosomes in meiosis
• Crossing over between homologous chromosomes is meiosis
• Environmental influence on gene expression (epigenetics)

Question 25

What is the definition of variation?

Answer 25

The differences between organisms of the same specie

Question 26

What is the definition of a selection pressure?

Answer 26

An environmental factor that can alter the frequency of alleles in a population, when it is limiting

Question 27

What is the definition of genetic drift?

Answer 27

Chance variations in allele frequencies in a population

Question 28

What is the definition of evolution?

Answer 28

A change in the average phenotype of a population

Question 29

What are the 3 types of natural selection?

Answer 29

• Stabilising selection - the average phenotype causes the greatest advantage
• Directional selection - an extreme phenotype becomes advantageous
• Disruptive selection - average phenotype is disadvantageous, a lower and higher value have advantages

Question 30

What are 2 types of reproductive isolation?

Answer 30

• Pre-zygotic - gametes are prevented from fusing so zygote never forms
• Post-zygotic - gametes fuse and zygote forms, but it i s sterile as the species don’t merge

Question 31

What is a hybrid?

Answer 31

The offspring of a cross between members of different species