Populations and Evolution

Question 1

Species?

Answer 1

A group of similar organisms that can reproduce to give fertile offspring.

Question 2

Population?

Answer 2

A group of organisms of the same species living in a particular area at a particular time, so they have the potential to interbreed.

Question 3

Gene pool?

Answer 3

The complete range of alleles present in a population.

Question 4

Allele frequency?

Answer 4

How often an allele occurs.

Question 5

Hardy-Weinberg princple?

Answer 5

A mathematical model that predicts that the frequency of alleles in a population wont change from one generation to the next provided that certain conditions.

Question 6

What conditions is the Hardy-Weinberg principle true under?

Answer 6

It has to be a large population where there’s no immigration, emigration, mutations and natural selection. And there needs to random mating, all possible genotypes can breed with all others.

Question 7

What does the Hardy-Weinberg principle estimate?

Answer 7

The frequency of particular alleles, genotypes and phenotypes within populations.

Question 8

The Hardy-Weinberg principle equation for allele frequency?

Answer 8

p + q = 1
p = the frequency of one allele (dominant)
q = the frequency of the other allele (recessive)

Question 9

The Hardy-Weinberg principle equation for genotype frequency?

Answer 9

p’2 + 2pq +q’2 = 1
p’2 = frequency of homozygous dominant genotype
2pq = frequency of heterozygous genotype
q’2 = frequency of homozygous recessive genotype

Question 10

Allele frequency and the Hardy-Weinberg principle?

Answer 10

The total frequency of all possible alleles for a characteristic in a certain population is 1.0. So the frequencies of the individual alleles e.g. the dominant one and the recessive one must add up to 1.

Question 11

Genotype frequency and the Hardy-Weinberg principle?

Answer 11

The total frequency of all possible genotypes for one characteristic in a certain population is 1.0. So the frequencies of the individual genotypes must add up to 1.

Question 12

How to work out phenotype frequencies?

Answer 12

The genotype frequencies can be used to work out the phenotype frequencies if you know how genotype relates to phenotype.

Question 13

The Hardy-Weinberg principle and co-dominance?

Answer 13

The Hardy-Weinberg equations can also be used to work out if the two alleles are co-dominant, or if you dont know which allele is recessive and dominant. In these situations you can just make p represent one allele and q represent the other.

Question 14

Variation?

Answer 14

The differences that exist between individuals.

Question 15

Intraspecific variation?

Answer 15

Variation within a species.

Question 16

What can variation be caused by?

Answer 16

Genetics and/or environmental factors.

Question 17

What is the main source of genetic variation?

Answer 17

Mutations, when changes in the DNA base sequence lead to the production of new alleles.

Question 18

Secondary source of genetic variation?

Answer 18

During meiosis, through the crossing over of chromatids and the independent segregation of chromosomes and because of the random fertilisation of gametes during sexual reproduction.

Question 19

What causes variation through the environment?

Answer 19

Food, climate and lifestyle.

Question 20

What does only genetic variation result in?

Answer 20

Evolution.

Question 21

Evolution?

Answer 21

The change in allele frequency in a population over time.

Question 22

Selection pressures?

Answer 22

Pressures that affect their chances of surviving such as disease, predation and competition.

Question 23

How can evolution occur?

Answer 23

By genetic drift and natural selection.

Question 24

Natural selection?

Answer 24

The process whereby an allele becomes common in a population because it codes for a characteristic that makes an organism more likely to survive, reproduce and pass on its genes to its offspring.

Question 25

What happens to those who are better adapted to the selection pressures?

Answer 25

Variation means some organisms are better adapted to selection pressures and means there are differential levels of survival and reproductive success in a population. Individuals who are better adapted are more likely to survive, reproduce and pass on their genes.

Question 26

What are the three types of natural selection?

Answer 26

Stabilising, directional and disruptive.

Question 27

Stabilising selection?

Answer 27

Where individuals with alleles for the characteristics towards the middle of the range are more likely to survive and reproduce. It occurs when the environment isn’t changing and it reduces the range of possible phenotypes.

Question 28

Directional selection?

Answer 28

Where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce. This could be in response in an environmental change.

Question 29

Disruptive selection?

Answer 29

Where individuals with alleles for extreme phenotype are more likely to survive and reproduce. It’s the opposite of stabilising selection because characteristics towards the middle of the range are lost. It occurs when the environment favours more than one phenotype.

Question 30

Speciation and diversity?

Answer 30

The diversity of life on earth today is the result of speciation and evolutionary change over millions of years. To start with there was one population of organisms. The population was divided and the new populations evolved into separate species. The new species were then divided again and the new populations evolved into more separate species. This process has been repeated over a long period of time to create millions of new species.

Question 31

Genetic drift and population size?

Answer 31

Natural selection and genetic drift work alongside each other to drive evolution, but one process can drive evolution more than the other depending on the population size. Evolution by genetic drift usually has a greater effect in smaller populations where chance has a greater influence. In larger populations any chance factors tend to even out across the whole population.

Question 32

Evolution via genetic drift?

Answer 32

Individuals within a population show variation in their genotypes. By chance, the allele for one genotype is passed on to more offspring than others. So the number 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 allele becomes more common in the population.

Question 33

Genetic drift?

Answer 33

The process whereby an allele becomes more common in a population due to chance.

Question 34

Sympatric speciation?

Answer 34

Sympatric speciation can occur when random mutations within a population prevent individuals that carry the mutation from breeding with other members of the population that dont carry the mutation. It doesnt involve geographical isolation. It is considered to be rare.

Question 35

Mechanisms of reproductive isolation?

Answer 35

Reproductive isolation occurs because changes in alleles, genotypes and phenotypes prevent individuals with these changes from successfully breeding with individuals without them. These changes include: seasonal changes, mechanical changes and behavioural changes.

Question 36

Seasonal changes and reproductive isolation?

Answer 36

Individuals develop different flowering or mating seasons or become sexually active at different rimes of the year. This means that they cant breed together are they arent reproductively active at the same time.

Question 37

Mechanical changes and reproductive isolation?

Answer 37

Changes in size, shape or function of genitalia can prevent successful mating, preventing individuals from breeding.

Question 38

Behavioural changes and reproductive isolation?

Answer 38

A group of individuals may, for example, develop courtship rituals that arent attractive to the rest of the species, such as change in song for birds. This prevents individuals from breeding with each other if they could do so successfully.

Question 39

Speciation?

Answer 39

The development of a new species from an existing species.

Question 40

Reproductively isolated?

Answer 40

This can occur when a physical barrier e.g. a flood or earthquake, divides a population of a species causing some individuals to become separated from the main population, known as geographical isolation.

Question 41

Allopatric speciation?

Answer 41

Where speciation occurs as a result of geographical isolation.

Question 42

What does geographical isolation lead to?

Answer 42

Over time, this can lead to speciation, the changes in allele frequency will lead to differences accumulating in the gene pools of the separated populations, causing changes in phenotype frequencies. Eventually, individuals from different populations will have changed so much that they wont be able to breed with one another to produce fertile offspring, they’ll have become reproductively isolated. The two groups will have become separate species.

Question 43

What occurs due to geographical isolation?

Answer 43

• different alleles will be more advantageous in the different populations so natural selection occurs. For example if geographical separation places one population in a colder climate than before, longer fur length will be beneficial. Directional frequencies will then act on the alleles for fur length in this population, increasing the frequency of the allele for longer fur length.
• allele frequencies will also change as mutations will occur independently in each population.
• genetic drift may also affect the allele frequencies in one or both populations.