Populations And Evolution

Question 1

What is a gene pool?

Answer 1

All the alleles of all the genes of all the individuals in a population at any one time are known as the gene pool.

Question 2

What is allele frequency?

Answer 2

The number of times an allele occurs within a gene pool is referred to as allelic frequency

Question 3

What is Cystic fibrosis?

Answer 3

One of the UKs most common life threatening inherited diseases

Question 4

What is Cystic fibrosis caused by?

Answer 4

A faulty gene that controls the movement of salt and water in and out of the cells within the body

Question 5

What does Cystic fibrosis do to people?

Answer 5

Affects the internal organs (Lungs and the digestive system) by clogging them with thick sticky mucus.
Makes it hard to breathe and digest food

Question 6

What are the possible allelic configurations, genotype and phenotype descriptions for the Cystic fibrosis gene?

Answer 6

Genotype- Homozygous dominant, Heterozygous, Homozygous recessive.
Phenotype- Not affected or affected

Question 7

What is the Hardy Weinberg equation?

Answer 7

• A mathematical equation that can be applied to calculate the frequencies of the alleles of a particular gene in a population
• It predicts the proportion of dominant and recessive alleles of any gene in a population remains constant from one generation to the next

Question 8

What does the Hardy Weinberg equation assume happens/ doesn’t happen in order to get representative results?

Answer 8

No mutations
The population is isolated, and there is no flow of allels into or out of the population
There is no selection likely to be passed on to the next generation
The population is large
Mating within the population is Random.

Question 9

What does the Hardy Weinberg Equation include?

Answer 9

P² + 2pq + q²= 1.0

Question 10

What does the letter p² stand for?

Answer 10

The dominant allele (homozygous dominant)

Question 11

What does the letter q² stand for?

Answer 11

The (homozygous) recessive allele

Question 12

What does 2pq mean?

Answer 12

The heterozygous allele

Question 13

What does the whole Hardy weinberg equation equal too?

Answer 13

One

Question 14

What are the main causes of genetic variation?

Answer 14

Individuals within a population of a species may show a wide range of variation in phenotype
This is due to genetic and environmental factors.

Question 15

What is phenotypic variation rarely due?

Answer 15

Rarely due to genetic or environmental factors acting alone. It is most typically a combination of the two.

Question 16

What is the equation that shows phenotype changes?

Answer 16

Phenotype= Genotype + Environmental

Question 17

How do genetic differences occur?

Answer 17

Within a population all individuals have the same genes however genetic differences occur because individuals will have different alleles of these genes.
When phenotypic variation is largely due to genetic factors, individuals fall into a number of distinct classes or categories with few intermediate forms.
Environmental factors have little influence on variation.

Question 18

How does the environment cause variation around the genotype?

Answer 18

Despite individuals falling into distinct classes due to their genotype, the environment often causes variation around this.
This causes classes to grade/ blur into one another, forming a continuum.

Question 19

What is an example of an environmental influence?

Answer 19

Height and mass which are often controlled by several genes. Environmental factors further influence the character often giving a normal distribution curve in large populations

Question 20

What are the key princles of the process of evolution by natural selection?

Answer 20

Organisms produce more offspring than can be supported by the environment= over production
There is genetic variation within the population
There is subsequently phenotypic variation within the population
An environmental factor (predation, competition and disease) results in differential survival and reproduction of individuals.

Question 21

What disadvantages can occur with a mutated allele and so impact allele frequency?

Answer 21

They are more easily found/ seen by predators, fewer survive and reproduce
They produce less offspring, so their offspring are less likely to survive and reproduce
The frequency of the advantageous allele will increase and the frequency of the disadvantageous allele will decrease
The favorable allele are therefore at a selective advantage

Question 22

How does reproductive success affect allele frequency?

Answer 22

1. Organisms produce more offspring than can be supported by the supply of food, light, nutrients and water
2. Despite overproduction of offspring most populations remain relatively constant in size.
3. This is because of intraspecific competition. Within any population of a species there will be a gene pool containing a variety of alleles.
4. Random mutations of alleles within the gene pool mean that some individuals will possess combinations of favorable alleles that make them more likely to survive in their competition with others
5. These individuals are more likely to obtain the available resources as they grow more rapidly and live longer. They will have a better chance of successfully breeding and producing more offspring.
6. Only those that survive and successfully reproduce will pass on their alleles to the next generation.
7. As these new individuals have favourable alleles, they in turn are more likely to survive and so reproduce successfully
8. It is the favourable alleles that gave the parents a selective advantage in competition for survival, that are most likely to be passed on to the next generation
9. Over many generations, the number of individuals with the favourable alleles will increase at the expense of the individuals with less advantageous alleles
10. Consequently, the frequency of the favourable alleles in the population increases while the frequency of the less favourable alleles decreases.

Question 23

What is a summary of reproductive success affecting allele frequency?

Answer 23

• Predation, disease and competition for the means of survival result in differential survival and reproduction (natural selection)
• Those organisms with phenotypes providing selective advantages are more likely to produce offspring and pass on their favourable alleles to the next generation
• This differential reproductive success caused changes is the allele frequencies within a gene pool.
• Evolution is a change in the allele frequency of a population

Question 24

What is natural selection?

Answer 24

It operates on most characteristics that organisms posses.
It results in populations being better adapted to their environment.

Question 25

What is directional selection?

Answer 25

Change in a population from one phenotype to another

Question 26

What is Stabilising selection?

Answer 26

A reduction of variation about an optimum modal value

Question 27

What is disruptive selection?

Answer 27

Favours extreme phenotypes at the expense of intermediate phenotypes.
Occurs when environmental factor takes two or more distinct forms
Can ultimately lead to formation of two separate species

Question 28

What is a species?

Answer 28

A group of organisms that can interbreed/ reproduce to give living fertile offspring.

Question 29

How does speciation occur?

Answer 29

1. The individuals of one species can freely interbreed as they share the same area
2. Climate change causes their habitat to be separated into two regions that become geographically isolated
3. The abiotic and biotic conditions within the two areas also become different, so different selection pressures exist in the two areas.
4. Within any population there is genetic variation caused by change genetic mutations of alleles
5. Mutations cause the production of a different polypeptide that give rise to different phenotypes. The selection pressures between the areas are different and as the environmental changes occur the phenotypes that are better able to survive are selected for
6. As these organisms survive they have a greater reproductive success
7. So in each of the isolated populations the frequency of the allele for the advantageous phenotype increases as the allele is passed on to future generations.
8. Over time, the differences between the gene pool become so great that the two populations are unable to interbreed and produce fertile living offspring- speciation has occured.

Question 30

What is genetic drift?

Answer 30

The change in allele frequencies due to chance events

Question 31

Where does genetic drift mainly occur and why?

Answer 31

In small populations because where chance plays a bigger role in which alleles are passed on from one generation to the next.
In small populations the relatively few members possess a smaller variety of alleles than large populations= lower genetic diversity.
The diversity of future generations is thus restricted to these few allels. With a smaller number of individuals, chance may play a bigger role in which alleles happen to be inherited. There can thus be significant fluctuation in allele frequency.

Question 32

What is genetic bottleneck?

Answer 32

A sharp reduction in the size of the population some alleles may lost, only a random subset survive. Allele frequencies thus changed.

Question 33

What is the founder effect?

Answer 33

When a population is descended from a small number of colonising ancestors. The alleles of all descendants are inherited from this small initial subset= low genetic variation.

Question 34

Explain why genetic drift is important in small populations but not in large populations…

Answer 34

The role of chance has a much bigger effect on a small population as one or two individuals represents a high proportion of alleles. In a large population a few individuals will not make a significant difference.

Question 35

What is geographical isolation?

Answer 35

Occurs when two populations become separated due to a physical barrier.

Question 36

What are some examples of geographical isolation?

Answer 36

Oceans, rivers, mountains, deserts

Question 37

What is one thing to remember with geographical isolation?

Answer 37

A barrier for one species may not be a barrier for another species (birds)

Question 38

What is allopatric speciation?

Answer 38

Occurs when two populations have become geographically separated due to a physical barrier. If environmental conditions vary on either side of a barrier natural selection influences two populations differently leading to local adaptation.

Question 39

What is Sympatric speciation?

Answer 39

Occurs in the same geographical area, but the different populations are reproductively isolated.

Question 40

Name 5 different types of isolation…..

Answer 40

Geographical
Ecological
Temporal
Behavioural
Mechanical
Gametic
Hybrid Sterility

Question 41

What is ecological isolation?

Answer 41

Populations inhabit different habitats within the same area and so individuals rarely meet

Question 42

What is temporal isolation?

Answer 42

The breeding seasons of each population do not coincide and so they don’t interbreed

Question 43

What is behavioural isolation?

Answer 43

Mating is preceded by courtship which is stimulated by the colour or markings of the opposite sex. Any mutations which cause variations in these patterns may prevent mating

Question 44

What is mechanical isolation?

Answer 44

Anatomical differences may prevent mating occurring (may be physically impossible)

Question 45

What is gametic isolation?

Answer 45

Gamete may be prevented from meeting genetic or biochemical incompatibility.

Question 46

What is hybrid sterility?

Answer 46

Hybrids formed from the fusion of gametes from different species are often sterile because they cannot produce viable gametes