Evolution & speciation

Question 1

Define evolution

Answer 1

a change in the allele frequency in response to selection pressure

Question 2

Who first suggested the theory of evolution? What is an example of how natural selection leads to evolution?

Answer 2

• the theory of evolution by natural selection was first suggested by Charles Darwin
• the peppered moth is an example of how natural selection leads to evolution over time

Question 3

Define population?

Answer 3

• all organisms of the same species living with one another in a habitat at the same time

Question 4

What does ‘survival of the fittest’ refer to?

Answer 4

survival of the fittest refers to individuals with characteristics that give them an advantage in surviving over others

Question 5

What does ‘fit’ mean?

Answer 5

fit means well adapted

Question 6

What is natural selection?

Answer 6

Natural selection is a process by which individuals with a favourable phenotype are more likely to survive and pass on their alleles to their offspring so that the advantageous alleles increase in frequency over time

Question 7

What is an allele?

Answer 7

• an allele is an alternative form of a gene that occurs at a specific position on a chromosome

Question 8

What does selection pressure refer to? What can this do to individuals with specific phenotypes?

Answer 8

• selection pressure refers to the environmental factors that affect the chance of survival of an organism
• selection pressures can increase the chance of individuals with a specific phenotype surviving and reproducing over others
• the advantageous alleles that code for the favourable phenotype will be passed on to offspring

Question 9

What are some examples of selection pressures?

Answer 9

• predation
• disease
• competition

Question 10

What does a gene pool consist of?

Answer 10

• a gene pool consists of all the alleles of all the genes present in a (interbreeding) population

Question 11

What does allele frequency mean?

Answer 11

• allele frequency refers to how often different alleles occur in the gene pool of a population

Question 12

What does adaptability refer to?

Answer 12

• certain alleles within a species population can produce features that make an organism better suited to its environment and therefore better able to survive and reproduce
• these features are known as adaptations

Question 13

How does reproductive isolation occur?

Answer 13

• reproductive isolation occurs when changes in the alleles and phenotypes of some individuals in a population prevent them from successfully breeding with other individuals in the population that dont have these changed alleles of phenotypes

Question 14

What are some examples of allele or phenotype changes that can lead to reproductive isolation?

Answer 14

• seasonal changes (become sexually active at different times of the year)
• mechanical changes (may develop changes in its genitalia)
• behavioural changes (may develop changes in their courtship behaviours, they can no longer attract the opposite sex)

Question 15

How can speciation occur?

Answer 15

• speciation can occur when populations of a species become separated from each other by geographical barriers

Question 16

What are some examples of geographical barriers?

Answer 16

• the barrier could be natural like a body of water, or a mountain range
• it could be man-made like a motorway

Question 17

What does interspecific and intraspecific refer to? And how does this relate to variation?

Answer 17

• variation refers to the differences between individuals
• it can be interspecific (between different species) or intraspecific (between individuals of the same species)

Question 18

What can be caused by random mutations?

Answer 18

• sometimes variation can be due to random mutations, which introduce new alleles into a population

Question 19

What can occur due to geographical isolation? What does this lead to?

Answer 19

• speciation can occur due to geographical isolation
• this separates two populations of the same species and as a result no gene exchange can occur between them
• if there are sufficient selection pressures acting to change the gene pools (and allele frequencies) within both these populations, then eventually they will diverge and form separate species

Question 20

What does the Hardy Weinberg principle state?

Answer 20

• The Hardy Weinberg principle states that if certain conditions are met, the allele frequencies of a gene within a population will not change from one generation to the next
• (basically that the allele frequencies will stay the same)

Question 21

What are the conditions that must be met for the Hardy Weinberg principle to be held true?

Answer 21

the conditions are:
- mating must be random
- the population is infinitely large
- there is no migration, mutation or natural selection

Question 22

What does it mean (based off of the Hardy Weinberg principle) if the allele frequencies in a population do change over time?

Answer 22

• if the allele frequencies in a population change over time, then it means that migration, mutation or natural selection has happened

Question 23

What are monohybrid characteristics?

Answer 23

• monohybrid characteristics are characteristics that are determined by one pair of alleles alone

Question 24

Why cant frequencies of characteristics that are dihybrid be predicted using the Hardy Weinberg principle?

Answer 24

• there are too many alleles/ possible combinations
• p and q only cover 2 alleles/ would need extra letters to denote other alleles
• there sill be too many phenotypes/ genotypes to predict with one equation

Question 25

If a mutation occurs, why would the Hardy Weinberg equation be no longer valid?

Answer 25

• mutations are changes in DNA sequences
• so new alleles will be created
• it will no longer be just 2 alleles that determine a characteristic

Question 26

What is the Hardy Weinberg equation? And what do the units stand for?

Answer 26

p2 + 2pq + q2 = 1
- the letter p represents the frequency of the (homozygous) dominant allele (B)
- the letter q represents the frequency of the (homozygous) recessive allele (b)
- the letters together pq represents the heterozygous alleles

Question 27

What has evolution increased?

Answer 27

• evolution by the process of natural selection has increased the variety of life on earth over time