7: GENETICS - EVOLUTION + SPECIATION

Question 1

What is evolution?

Answer 1

change in the frequency of an allele in a population over time

Question 2

What are the 5 key processes that can result in evolution?

Answer 2

• genetic drift
• assortative (non-random) mating
• mutation
• gene flow
• natural selection

Question 3

What is a selection pressure?

Answer 3

a factor that affects an organisms chance of survival (eg: predation, disease, competition)

Question 4

What are the 3 types of natural selection?

Answer 4

• stabilising selection
• directional selection
• disruptive selection

Question 5

What is disruptive selection?

Answer 5

• natural selection where individuals with alleles for both extremes are likely to survive and reproduce
• characteristics in the middle of the range are lost
• occurs when the environment favours more than 1 phenotype
• occurs when environmental conditions fluctuate/selection pressures are variable

Question 6

What is genetic drift?

Answer 6

instead of environmental factors affecting which individuals survive, breed and pass on their alleles, chance dictates which alleles are passed on

Question 7

Describe the process of genetic drift

Answer 7

• individuals within a population show variation in their genotypes
• by chance, the allele for 1 genotype is passed on to more offspring than the others so the no. of individuals with the allele increases
• if by chance the same allele is passed on more often again and again, it can lead to evolution as the freq of the allele in the population increases

Question 8

Why is a larger gene pool more beneficial than a small gene pool?

Answer 8

• larger gene pool increases survival as a population
• small population results in reduced fitness so it increases risk of extinction

Question 9

Why does genetic drift have a greater influence in smaller populations than in larger ones?

Answer 9

• chance has greater influence in smaller populations
• genetic drift tends to cause decrease in genetic diversity, so species is less likely to have selective advantage for any future changes in environment

Question 10

What is speciation?

Answer 10

• the development of a new species from an existing species
• occurs when populations of the same species become reproductively isolated

Question 11

What is reproductive isolation?

Answer 11

• when populations cannot interbreed to produce fertile offspring
• occurs because changes in alleles, genotypes and phenotypes prevent individuals with these changes from successfully breeding with individuals without them

Question 12

What 4 things can lead to reproductive isolation?

Answer 12

• geographical isolation
• seasonal changes (individuals can develop different flowering/mating seasons/become sexually active at different times of the year meaning that they can’t breed together as they aren’t reproductively active at the same time)
• mechanical changes (changes in the size/shape/function of genitalia/reproductive organs can prevent successful mating)
• behavioural changes (a group of individuals may for example develop courtship rituals that aren’t attractive to the rest of the species which prevents individuals from breeding together even if they could do so successfully)

Question 13

What are the 2 types of speciation?

Answer 13

• allopatric speciation
• sympatric speciation

Question 14

What is allopatric speciation?

Answer 14

• speciation that occurs when a population becomes geographically isolated by a physical barrier resulting in reproductive isolation
• populations experience different selection pressures
• natural selection occurs independently in each population
• different changes in allele frequencies occur in each population
• eventually individuals from the different populations will be so different that they won’t be able to reproduce to give fertile offspring

Question 15

What is sympatric speciation?

Answer 15

• speciation that occurs when a population becomes reproductively isolated without any physical separation
• random mutations within a population prevent individuals carrying the mutation from breeding with other members of the population