7B Populations and Evolution

Question 1

Define allele frequency

Answer 1

how often an allele appears in a population

Question 2

define evolution

Answer 2

the process by which organisms become more adapted to their environment over time

Question 3

define speciation

Answer 3

the formation new species

Question 4

define variation

Answer 4

the measure by which organisms differ

Question 5

name the sources of variation

Answer 5

1. most commonly due to mutations
   changes in the genotype often lead to changes in the phenotype
   these can be advantageous or disadvantageous and might be inherited
2. meiosis
   random mixing of chromosomes
3. random fertilisation

Question 6

What is differential reproductive success?

Answer 6

The difference between an organism in which a variation was a benefit and an organism in which the same variation was a disadvantage

Question 7

Describe natural selection

Answer 7

alleles offering an advantage are more likely to be inherited, this leads to an increase in the allele frequency
this process that leads to the change in frequency is natural selection

Question 8

describe selection pressure

Answer 8

Changes due to variation can fore an entire population to adopt the new phenotype or for extreme phenotypes to be lost

Question 9

What are the three types of selection?

Answer 9

directional, stabilising, disruptive

Question 10

Describe directional selection

Answer 10

an extreme phenotype is favoured and the mean shifts to one side, usually as a result of environmental changes

Question 11

Describe stabilising selection

Answer 11

Where extreme phenotypes reduce in frequency and the mean is favoured, due to a stable environment

Question 12

Describe disruptive selection

Answer 12

Both extremes of a phenotype are favoured and the ‘mean’ reduces in frequency, results in almost two separate population

Question 13

Define gene pool

Answer 13

term used to describe the collection of all genes present in all species of a population

Question 14

Describe the process of speciation

Answer 14

when there is a large change in the allele frequency, this could lead to the creation of a new species
Two individuals must become reproductively isolated and have very different one pools to become different species

Question 15

What are the two types of speciation?

Answer 15

Allopatric and sympatric

Question 16

Describe allopatric speciation

Answer 16

Geographic isolation, leading to different environments, eg natural event like earthquake or volcano, or a new species landing on island
no genetic drift between individuals, variation increases as species adapt

Question 17

Describe sympatric speciation

Answer 17

doesn’t require geographic isolation, instead one species gains a mutation that gives them an advantage and allows them toil a new niche
the ancestral population do not benefit from the new niche and continue without the mutation allowing both populations to drift apart

Question 18

Describe artificial selection

Answer 18

evolution isn’t always a natural process,
humans often force breeding between organisms to produce beneficial breeds, this is selective breeding

Question 19

Describe genetic drift

Answer 19

only happens in small population,
the gains or losses of alleles in individuals causes a significant allele frequency change of the population
a genetic drift from the norm