genes2

Question 1

Define directional selection. Under what circumstances?

Answer 1

= Selection favouring individuals that vary in one direction from the mean of the population.

=> changes overall characteristics in the population.

• Change in environmental conditions —> phenotypes that are best suited to new conditions are most likely to survive and reproduce —> mean will then move in direction of offspring over time.

Question 2

Outline an example of directional selection. Draw normal distribution curves to represent the change.

Answer 2

• Antibiotic resistance with penicillin:
  1. Spontaneous mutation in allele of a gene in a bacterium —> new protein (enzyme - penicillinase) produced.
  2. Bacterium in situation where penicillin being used to treat an individual (by chance) —> mutation gives bacterium an advantage as it can produce penicillinase and survive.
  3. Surviving bacterium divides by binary fission —> small population of resistant bacteria forms.

4. Population of resistant bacteria grows at expense of non-resistant population
   => allele frequency of penicillinase allele increases in the population.

=> normal distribution curve shifts in direction of higher penicillin resistance.

=> antibiotic use places a directional selection pressure on the bacterial population.

Question 3

Define stabilising selection. Under what circumstances?

Answer 3

= Selection favouring individuals with the average characteristic of the population.

=> preserves overall characteristics of the population.

• Stable environmental conditions —> phenotypes closest to mean are favoured => tends to eliminate the phenotypes at the extremes as phenotypes around mean selected for.

Question 4

Outline an example of stabilising selection. Draw normal distribution curves to represent the change.

Answer 4

• Human birth weights:
  1. Infant mortality rate lowest in range 2.5-4.0 kg and increases either side of this range.
  2. Mortality rate is greater at the two extremes => population’s characteristics are being preserved rather than changed —> phenotypes around the mean of the population selected for and those at both extremes selected against.

=> normal distribution curve in the same position on x-axis but narrower range of distributions.

Question 5

What is the consequence of natural selection?

Answer 5

=> Results in species better adapted to the environment in which they live.

Question 6

Adaptations may be:

Answer 6

1. Anatomical.
2. Physiological.
3. Behavioural

Question 7

Example of anatomical adaptations.

Answer 7

• Shorter ears and thicker fur in arctic foxes compared to foxes in warmer climates

Question 8

Example of physiological adaptations.

Answer 8

• Kangaroo rats oxidise fat —> produces water as a by-product in a dry desert environment.

Question 9

Example of behavioural adaptations.

Answer 9

• Autumn migration of swallows from the UK to Africa to avoid food shortages in UK winter.

Question 10

Describe how genetic bottlenecks reduce genetic diversity.

Answer 10

= Genetic Bottleneck is an event that causes a big reduction in a population —> when a large number of organisms within a population die before reproducing.

=> reduces the number of different alleles in the gene pool and so reduces genetic diversity.

=> the survivors reproduce and a larger population is created from a few individuals.

Question 11

Explain the Founder Effect.

Answer 11

= Type of genetic bottleneck.

= Describes what happens when just a few organisms from a population start a new colony and there are therefore only a small number of different alleles in the initial gene pool.

=> the frequency of each allele in the new colony might be very different to those alleles in the original population —> could possibly lead to a higher incidence of genetic disease.

• The founder effect could occur as a result of migration leading to geographical separation or if a new colony is separated from the original population for another reason, such as religion.

Question 12

Define Phylogeny.

Answer 12

= Study of evolutionary history of groups of organisms.

=> tells which organisms are related to each other and how closely related they are.

Question 13

What is a phylogenetic tree?

Answer 13

= Tree showing the relationship between organisms.

1. First branching point represents common ancestor for all the members of the family - which is now extinct.
2. Each of the following branch points represents another common ancestor from which a different group diverged.
3. Closely related species diverged away from each other most recently —> branches are closer together.

Question 14

Define taxonomy.

Answer 14

= Science of classification - involves naming organisms and organising them into groups.

NB => Scientists now take into account phylogeny when classifying organisms and group organisms according to their evolutionary relationships.

Question 15

Why do we classify organisms?

Answer 15

= Makes it easier to identify, study and compare organisms with others

Question 16

What are the 8 taxa? How are they arranged?

Answer 16

Taxa = hierarchal levels of groups used to classify organisms.

Domain
Kingdom
Phylum
Class
Order
Family
Genus 
Species

= Arranged in a hierarchy, with the largest groups on top.

= Organisms can only belong to one organism in the group at each level in the hierarchy - no overlap.

Question 17

How are organisms classified?

Answer 17

1. Organisms first sorted into three large taxa = domains - Eukarya, Bacteria and Archaea.
2. Related organisms in a domain are then organised into slightly smaller groups called kingdoms (based on shared characteristics).
3. More closely related organisms from that kingdom then grouped into a phylum etc. and so on.
4. Hierarchy ends with species - groups that contain only one type of organism.

Question 18

What changes do we see as we move the down the hierarchy?

Answer 18

= More groups at each level, but fewer organisms in each group —> organisms in each group become more closely related.

Question 19

Define species.

Answer 19

= Group of similar organisms able to reproduce to fertile offspring.

Question 20

Why do scientists constantly update classification systems?

Answer 20

= Scientists constantly update classification systems because of discoveries about new species and new evidence about known organisms —> DNA sequence data etc.

Question 21

Comment on the Binomial Naming system.

Answer 21

= One internationally accepted name - helps to avoid confusion of using common names - over 100 plant species called raspberries etc.

1. First part = genus, capital letter.
2. Second part = species, lower case.

NB => names always written in italics or underlined if handwritten.

Question 22

What is Courtship Behaviour? What is its purpose?

Answer 22

= Set of species-specific display behaviours in which an animal attempts to attract a mate of the same species and exhibit their desire to copulate.

1. Can be as simple as releasing certain chemicals or as complex as a series of displays.
2. Species-specific => only members of the same species will respond to that courtship behaviour.

=> allows members of the same species to recognise each other, preventing interbreeding —> making reproduction more successful (mating with another species will produce infertile offspring).

Question 23

How can Courtship Behaviour be used to help classify species?

Answer 23

= Species-specific = so we can observe particular display behaviours of two species and compare them - more closely related two species are, the more similar their courtship behaviour will be.

Question 24

List the 3 ways in which advances in technologies/techniques can clarify evolutionary relationships.

Answer 24

1. Genome sequencing.
2. Comparing amino acid sequence.
3. Immunological comparisons.

Question 25

Outline how Genome Sequencing can clarify evolutionary relationships.

Answer 25

1. Entire base sequence of DNA can be determined (due to GS advances).
2. DNA base sequence of one organism can be compared to DNA base sequence of another organism to see how closely related they are.

=> closely related species will have a higher % of similarity in their DNA base sequence.

=> can clarify evolutionary relationships - can compare DNA base sequences of one organism with others in same family (for example) —> if significantly different then can be reclassified.

Question 26

Outline how Amino Acid Sequences can clarify evolutionary relationships.

Answer 26

1. Proteins made of amino acids —> sequence of amino acids in a protein is coded for by the DNA base sequence.
2. Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins.
3. Cytochrome C, for example. The more similar the amino acid sequence of cytochrome C in two different species —> more closely related species are likely to be.

Question 27

Outline how Immunological Comparisons can clarify evolutionary relationships.

Answer 27

• Antibodies of one species will respond to specific antigens on proteins, such as albumin, in the blood serum of another.
  1. Serum albumin from species A injected into B.
  2. Species B produces antibodies specific to all antigen sites on species A’s albumin.
  3. Serum extracted from species B, containing antibodies specific to the antigens on the species A albumin.
  4. Serum from species B mixed with serum from species C blood.
  5. Antibodies respond to their corresponding antigens on albumin in series of species C.
  6. Number of similar antigens —> more precipitate formed —> more closely-related species.

Question 28

How have Gene Technologies changed the way in which genetic diversity is assessed?

Answer 28

Genetic diversity = number of different alleles in a population.

1. In the past, estimates of genetic diversity made by looking at frequency of measurable/observable characteristics in a population.
2. Different alleles determine different characteristics —> wide variety of different variations in a characteristic in a population —> indicates a high number of different alleles and therefore a high genetic diversity.
3. BUT, we can now measure genetic diversity directly with gene technologies:

• Different alleles of same gene have slightly different DNA base sequences.
• Comparing DNA base sequences of same gene in different organisms in a population —> can see number of different alleles of that gene in a population.
• Different alleles also produce slightly different mRNA base sequences and may produce proteins with slightly different amino acid sequences —> can also be compared.

=> new technologies can all be used to give more accurate estimates of genetic diversity within a population or species —> also allow the genetic diversity of different species to be compared more easily.

Question 29

What are the main causes of variation?

Answer 29

1. Genetic factors:

• different species have different genes —> interspecific variation.
• individuals of same species have same genes, but different alleles —> intraspecific variation.

2. Environmental factors:
   - Differences in climate, food, lifestyle.

=> most intraspecific variation caused by a combination of genetic and environmental factors.

Question 30

Define intraspecific variation.

Answer 30

= Members of the same species differing from one another.

Question 31

Define interspecific variation.

Answer 31

= One species differing from another.

Question 32

How can we study variation in a population?

Answer 32

=> Must sample a population:

• Would be too time-consuming/impossible to get all the individuals in the population to compare.
• Therefore, need to get a (representative as possible) sample of the population.

Question 33

Outline random sampling process.

Answer 33

= Taking measurements of individuals, randomly selected from the population of organisms being investigated.

1. Divide area into grid of numbered lines.
2. Use a computer to generate a random series of co-ordinates.
3. Take samples at the intersections of these co-ordinates.

NB => measurements can be relied upon if individuals sampled are representative of the population.

Question 34

Why is RANDOM sampling necessary?

Answer 34

1. Avoid sampling bias - selection process is likely to have a degree of bias, whether done deliberately or unwittingly - may be making unrepresentative choices.

NB => To ensure any variation observed in the sample is not simply due to chance —> can analyse results statistically to be more confident that sample representative of entire population.

Question 35

How can we minimise the effect of chance in the sampling process?

Answer 35

Cannot completely remove chance from the sampling process but can minimise its effect by:

1. Using a larger sample size —> smaller probability that chance will influence result so anomalous results have less influence => more reliable data.
2. Analysing the collected data —> analysis done through use of statistical tests to determine the extent to which chance may be influencing data.

=> allow us to decide whether any variation observed is the result of chance or has been caused by some other factor.

Question 36

What do bell shaped normal distribution curves show (in terms of variation)?

Where are mean, mode and median measured on bell-shaped and skewed normal distribution curves?

Answer 36

• If bell-shaped, shows us continuous variation.
  1. Bell-shaped:
• Mean, mode and median all down central line (bisector) of curve.
  2. Skewed (to right):
• Mode at highest peak.
• Mean to left of mode (estimate - like Maxwell-Boltzmann distribution).
• Median to left of mean, exactly halfway along x axis line covered by curve.

Question 37

What does standard deviation show us?

What is it shown by on a normal graph?

What is it shown by on a normal distribution curve?

Answer 37

=> Standard deviation shows us how much the values in a simple sample vary - it is a measure of the spread of values about the mean.

=> On normal graphs, shown by error bars.

=> On normal distribution curves, SD is the difference between the mean point of curve (bisector for bell-shaped) and the point where curve goes from convex —> concave (point of inflexion).

Question 38

Define biodiversity.

Answer 38

= Variety of living organisms in an area.

Question 39

Define community.

Answer 39

= All the populations of different species in a habitat.

Question 40

Local biodiversity.

Answer 40

= Variety of different species in a local, small habitat.

Question 41

Global biodiversity.

Answer 41

= Variety of species on Earth - total number of different species - 8.7 million.

Biodiversity is greatest at the equator and decreases towards the poles.

Question 42

Define species richness. How can it be worked out?

Answer 42

= Measure of the number of different species in a community.

Can be calculated by taking random samples of a community and counting the number of different species.

Question 43

How can we find the index of diversity?

Answer 43

d = N(N-1) / SUM n(n-1)

Where:

N = Total number of organisms of all species.

n = Total number of organisms of each species.

=> Higher number = more diverse the area is.
=> d = 1 if all individuals are of the same species.

Question 44

How can agricultural practices reduce biodiversity?

Answer 44

1. Woodland clearance - increases area of farmland, but directly reduces number of trees and tree species - destroying habitats, shelters and food sources.
2. Hedgerow removal - done to increase area of farmland - reduces biodiversity and destroys habitats, shelters and food sources.
3. Pesticides - reduces diversity as pests killed. Any predators with pests as prey will lose out.
4. Herbicides - reduces diversity as unwanted plants / weeds killed - eliminates food source also.
5. Monoculture - Farmers have fields containing only one type of plant —> single type of plant reduces biodiversity directly and will support fewer organisms - either as a habitat or food source.

Question 45

How can we balance out conservation and agriculture?

Answer 45

1. Giving legal protection to endangered species.
2. Creating protected areas such as SSSIs (Sites of Special Scientific Interest) and AONBs (Areas of Outstanding Natural Beauty) => restrict further development, including agricultural development.
3. Environmental Stewardship scheme which encourages farmers to conserve biodiversity - by planting hedgerows and leaving margins around fields for vegetation to grow.