5. On the Wild Side (4)

Question 1

Natural Selection

Answer 1

the process by which organisms that are better adapted to their environment survive, reproduce, and pass on their advantageous alleles, causing advantageous characteristics to increase in frequency within a population

Question 2

Stages of natural selection

Answer 2

• Natural selection can only take place if variation is present
• Variation results from small differences in DNA base sequences between individual organisms within a population
• Selection pressures are environmental factors that influence survival chances
• ‘survival of the fittest ‘variation present= some individuals will have characteristics that make them better adapted for survival
• these fitter individuals more likely to reproduce, pass on alleles for advantageous characteristics

-number of individuals in population with this characteristic increase in frequency

Question 3

Where do the sources of variation come from?

Answer 3

Mutation, Meiosis, Random fertilisation during sexual reproduction

Question 4

Types of environmental factors that act as selection pressures

Answer 4

predation, competition for food, and disease

Question 5

Evidence of evolution

Answer 5

Fossil records, antibiotic resistance, molecular evidence, evidence from gene/ protein sequences

Question 6

Fossil records

Answer 6

for transitional species, showing how one species could evolve into another

Question 7

Antibiotic resistance

Answer 7

 If a bacterial infection is treated with an antibiotic, a bacterial individual with a random mutation for antibiotic resistance is likely to survive and reproduce

 The antibiotic acts as a selection pressure

 The bacterial cell with the resistance mutation will pass on the mutation and cause antibiotic resistance to increase in frequency in the population
(evolution by natural selection)

Question 8

Molecular evidence

Answer 8

 DNA and proteins show similarities between species that indicate evolution of species from a common ancestor

Question 9

Evidence from gene sequences

Answer 9

o Similar base sequences = indicates common ancestry
o The level of similarity between base sequences of equivalent genes can give a measure of how long ago two species diverged from each other during speciation

Question 10

Genomics

Answer 10

DNA sequencing to determine the sequence of bases that make up a gene

Question 11

Gene similarity and divergence time

Answer 11

 Genes with very similar base sequences are likely to have diverged recently
 Genes with very different base sequences are likely to have diverged a long time ago
 Species that share a recent common ancestor are more… closely related

Question 12

Evidence from protein sequences

Answer 12

• In proteomics it is possible to sequence proteins; this determines the order of amino acids in the primary structure of a protein
• This is used to determine evolutionary relationships in the same way as DNA sequences (amino acid sequences can indicate gene sequencing)
• indicator of common ancestry/ how long ago two species diverged from each other

Question 13

proteomics

Answer 13

study of proteins

Question 14

How are theories validated by the scientific community

Answer 14

-Reading scientific journals
- peer review: checking if results are valid and analysed properly
- repetition to check that their results are reliable
- Attending scientific conferences for discussions

Question 15

Speciation process

Answer 15

• the development of new species from pre-existing species over time
• two populations of the same species are isolated from each other in some way
• there can no longer be an exchange of genes/ gene flow between the two populations

Question 16

What might Isolation of populations may occur as a result of

Answer 16

• allopatric speciation- Geographical isolation
• sympatric speciation - Random mutations that prevent them from interbreeding with each other

Question 17

How does genetic drift affect allele frequencies:

Answer 17

• Populations that are isolated from each other may face different selection pressures in their environment

The different environmental conditions for the two populations might mean that different alleles are advantageous ( natural selection)

Allele frequencies change as a result as disadvantage alleles don’t survive/ pass on characteristics.

Question 18

What is speciation?

Answer 18

the two populations begin to differ physiologically, behaviourally and morphologically to such an extent that they can no longer interbreed to produce fertile offspring; speciation has occurred

Question 19

Allopatric speciation

Answer 19

• speciation occurs as a result of geographical isolation caused by geographical borders
• No gene flow is taking place The two populations experience different environments, so different alleles become advantageous
• Allele frequencies in the gene pools of the two populations may change in different ways due to
  Different selection pressures acting on them and the accumulation of random changes resulting from genetic drift

Question 20

Changing allele frequencies will lead to what?

Answer 20

changes in the phenotypes of the two populations

Question 21

Sympatric speciation

Answer 21

• Sympatric speciation takes place with no geographical barrier - i.e. seasonal changes, mechanical changes, behavioural changes.
• The populations may still live in the same habitat but they are isolated from each other in the sense that they do not interbreed

Question 22

Seasonal changes

Answer 22

• their reproductive (mating/ flowering) timings no longer match up

Question 23

Mechanical changes

Answer 23

Some individuals in a population may develop changes in their genitalia that prevent them from mating successfully

Question 24

Behavioural changes

Answer 24

Change in courtship behaviours meaning they can no longer attract individuals of the opposite sex for mating