3.4.7 - investigating diversity

Question 1

How can comparison of base sequences be used to investigate how closely related organisms are?

Answer 1

patterns in the sequences can be compared
- due to mutations the sequence of bases can change over time
- new species will accumulate more and more differences
- so species that are more closely related will show more similarity in their DNA (more closely related = higher percentage or similarity)

Question 2

How can comparison of amino acid sequences in proteins be used to investigate the relationship between organisms?

Answer 2

patterns in the amino acid sequences can be compared as the sequence of amino acids is determined by mRNA which is determined by DNA

Question 3

How are immunological comparisons used to investigate variations in proteins?

Answer 3

• similar proteins will bind to the same antibodies - if antibodies from a human protein are added to isolated samples from another species and they bind, the two species must be similar

Question 4

How can comparing observable characteristics be used to investigate how closely related organisms are?

Answer 4

each characteristic is determined by a gene and variety of the trait depends on the number andd variety of alleles

Question 5

What are the limitations of using observable characteristics to group species?

Answer 5

• unreliable - some species are coded for by more than one gene (polygenic)
• environmental influence on phenotype
• convergent evolution

Question 6

What is variation and give the two types?

Answer 6

difference between individuals
- interspecific (between different species)
- intraspecific (within species)

Question 7

Causes of variation

Answer 7

• genetic - controlled by alleles of a single gene
• environmental
• Both (eg height)

Question 8

What is sampling and why is it used?

Answer 8

taking measurements from individuals selected from a population (acts as a model for the whole population)

Question 9

What two issues can arise when sampling and how is this resolved?

Answer 9

1. chance - can be caused by a too small sample size - use a larger sample to ensure it is more reliable and representative - use statistical tests to determine influence of chance
2. sampling bias - if samples are not taken at random - use a random sampling method

Random sampling method - divide area into a grid and generate random coodinates

Question 10

Define normal distribution

Answer 10

values either side of the mean, creating a bell shaped curve (normal distribution is symmetrical about the mean)

Question 11

What are the issues with using the range and the mean ?

Answer 11

• range only shows the highest and lowest values
• mean fails to consider the variation of values within a sample

Question 12

What do the mean and standard deviation show on a normal distribution curve?

Answer 12

• mean - maximum height of the curve
• standard deviation - width of curve - range of values either side of the mean

Question 13

What does a large standard deviation indicate?

Answer 13

• measurements are more spread about the mean
• so the data is not as reliable

Question 14

The error bars showing the standard deviation do not overlap - what does this indicate ?

Answer 14

there IS a SIGNIFICANT difference between the mean of two or more sets of data and the difference is not due to chance