Genetic Information and Variation - Investigating Diversity

Question 1

What is interspecific variation?

Answer 1

when one species differs from another

Question 2

What is intraspecific variation?

Answer 2

when members of the same species differ from each other

Question 3

Why do you have to take many measurements of the same thing?

Answer 3

because usually you are measuring some aspect of living organisms and all living organisms are different

Question 4

What is sampling?

Answer 4

Sampling involves taking measurements of individuals, selected from the population of organisms which is being investigated. In theory, if these individuals are representative of the population as a whole, then the measurements can be relied upon.

Question 5

How does sampling bias make measurements unrepresentative?

Answer 5

The selection process may be biased. The investigators may be making unrepresentative choices, either deliberately or unwittingly.

Question 6

How does chance make measurements unrepresentative?

Answer 6

Even if sampling bias is avoided, the individuals chosen may (by pure chance) not be representative.

Question 7

How can you prevent sampling bias?

Answer 7

The best way to prevent sampling bias is to eliminate, as far as possible, any human involvement in choosing the samples. This can be achieved by carrying out random sampling.

Question 8

Describe a method of taking a random sample.

Answer 8

1. Divide the study area into a grid of numbered lines, for example by stretching two long tape measures at right angles to each other.
2. Using random numbers, from a table or generated by a computer, obtain a series of coordinates.
3. Take samples at the intersection of each pair of coordinates many times.

Question 9

How can you minimise the effect that chance has on the sampling process?

Answer 9

We cannot completely remove chance from the sampling process but we can minimise its effect by:

• Using a large sample size: The more individuals that are selected, the smaller is the probability that chance will influence the result, and the less influence anomalies will have. The greater the sample size, the more reliable the data will be.
• Analysis of the data collected: Accepting that chance will play a part, the data collected can be analysed using statistical tests to determine the extent to which chance may have influenced the data. These tests allow us to decide whether any variation observed is the result of chance or is more likely to have some other cause.

Question 10

What is the normal distribution curve?

Answer 10

• bell-shaped
• symmetrical around a central value
• skewed distribution is when the curve is shifted slightly to one side
• point of inflection will be exactly one standard deviation away from the mean on a curve if it’s a normal distribution

Question 11

What is the arithmetic mean?

Answer 11

the sum of the sampled values divided by the number of items

Question 12

What is the median?

Answer 12

the central or middle value of a set of values in ascending order

Question 13

How do normal distribution curves differ from each other?

Answer 13

A normal distribution curve always has the same basic shape. It differs in two measurements: its maximum height and its width.

Question 14

What is the mean?

Answer 14

The mean is the measurement at the maximum height of the curve. The mean of a sample data provides an average value and is useful information when comparing one sample with another. It does not, however, provide any information about the range of values within the sample.

Question 15

What is the standard deviation?

Answer 15

The standard deviation is a measure of the width of the curve. It gives an indication of the range of values either side of the mean (spread of raw data). A standard deviation is the distance from the mean to the point where the curve changes from being convex to concave (the point of inflection).

68% of all the measurements lie within +/- 1.0 standard deviation. Increasing this width to almost +/- 2.0 standard deviations takes in 95% of all measurements.

To calculate the standard deviation with any accuracy there needs to be a minimum number of values.

Question 16

What does a large and small standard deviation mean?

Answer 16

A large standard variation means a lot of variety, while a small standard deviation means little variety.

Question 17

What must you record when using quadrats?

Answer 17

• number of species present in quadrat
• number of organisms of an individual species
• percentage coverage by a species
• measure a characteristic of an individual

Question 18

What can you conclude when using quadrats?

Answer 18

• amount of variation present

- the effect of genetic and environmental factors

Question 19

Why is an average calculated?

Answer 19

so data can be compared with other samples

Question 20

What are the benefits of statistical tests?

Answer 20

• they provide an unbiased and objective way of drawing a conclusion
• they give you the probability of the results being due to random chance
• your conclusion is not a subjective judgement based on your opinion

Question 21

When is a student t-test used?

Answer 21

• used for normally distributed continuous data

- used when looking for a significant difference between two means

Question 22

What is “t” a measure of?

Answer 22

• “t” is a measure of how significant the difference is between two means, by taking into account each sample’s standard deviation
• the significance is measured as a probability that the difference was due to random chance

Question 23

What is needed to carry out a t-test?

Answer 23

• there must be enough data that a reliable mean can be calculated and it should be normally distributed
• the number in each sample does not need to be the same, but will ideally be more than 15 samples in each set

Question 24

When is spearman’s rank used?

Answer 24

• used when looking for a significant correlation between two sets of continuous data on a graph
• used for normally distributed continuous data

Question 25

When is the chi test used?

Answer 25

• used when looking for a significant difference between the frequency of individuals in different categories
• it calculates the probability of your results being obtained if the null hypothesis is true
• it compares your results with the result you would expect if there was no difference (from the null hypothesis)

Question 26

What equation do you use in the chi2 test?

Answer 26

χ2= ∑ [(O-E)2/E]

O: observed result
E: expected result

Question 27

What are the features of a student t-test?

Answer 27

• type of data?: continuous (normal distribution)
• how is data presented?: bar chart
• significant difference between?: two means
• how are degrees of freedom calculated?: (n1 + n2) - 2

Question 28

What are the features of spearman’s rank?

Answer 28

• type of data?: continuous
• how is data presented?: line graph
• significant difference between?: n/a (significant correlation)
• how are degrees of freedom calculated?: n/a (pairs of measurements)

Question 29

What are the features of the chi2 test?

Answer 29

• type of data?: categoric (frequency of individuals)
• how is data presented?: bar chart
• significant difference between?: number of individuals in different categories
• how are degrees of freedom calculated?: (number of categories - 1)

Question 30

How can you investigate diversity?

Answer 30

• comparison of observable characteristics
• comparison of DNA base sequences
• comparison of the base sequence of mRNA
• comparison of amino acid sequences in proteins encoded by DNA and mRNA

Question 31

What is comparison of observable characteristics based on?

Answer 31

The fact that each observable characteristic is determined by a gene or genes (with environmental influence). The variety within a characteristic depends on the number and variety of alleles of that gene (plus environmental influences).

Question 32

What are the limitations of using observable characteristics?

Answer 32

• polygenic (coded for by more than one gene)
• not discrete and vary continuously
• difficult to distinguish one from another
• characteristics may be modified by the environment

Question 33

How has gene technology caused a change in the methods of investigating genetic diversity?

Answer 33

DNA differences from measurable or observable characteristics has been replaced by direct investigation of DNA sequences.

Question 34

How can you compare species using their DNA code?

Answer 34

• dna hybridisation
• extract dna of both species and heat
• hydrogen bonds are the first to break
• mix the single stranded dna and cool
• if species A and B have enough bases in common, the single strands of each will form hydrogen bonds (hybrid dna) between the complementary bases

Question 35

How do you compare amino acid sequences in proteins?

Answer 35

The sequence of amino acids in proteins is determined by mRNA which is determined by DNA. Genetic diversity within, and between, species can therefore be measured by comparing the amino acid sequences of their proteins.

• the more similar the sequence of amino acids in a particular protein, the more closely related the species are
• e.g. comparing haemoglobin in different mammals

Question 36

How can you identify closely related species using DNA sequencing?

Answer 36

Species that are more closely related show more similarity in their DNA base sequences than species that are more distantly related.

Question 37

How can you compare the base sequence of mRNA?

Answer 37

mRNA is coded for by DNA. The base sequences on mRNA are complementary to those of the strand of DNA from which they were made. So you can measure DNA diversity, and so genetic diversity, by comparing the base sequence of mRNA.