Evolution and variation

Question 1

What is the theory of evolution via natural selection and who proposed it?

Answer 1

Organisms best suited to environment are more likely to survive, reproduce, and pass on advantageous characteristics to offspring

Darwin and Wallace

Question 2

What is palaeontology?

Answer 2

Study of life’s history as recorded in fossils involving examining organisms preserved in rock layers showing how organisms have gradually changed

Question 3

What is evidence for evolution in the fossil records?

Answer 3

• simple bacteria and algae fossils are found in oldest rocks, progressing to more complex vertebrates in newer rocks
• plant fossils appear before those of animals that feed on these plants, indicating a natural order of evolution

Question 4

Why is the fossil record incomplete?

Answer 4

• organisms decompose before they can fossilise
• fossilisation uncommon due to specific conditions for organism preservation
• many fossils have been lost due to erosion or geological processes
• many organisms have not yet been discovered
• certain organisms especially with soft bodies less likely to fossilise leading to gaps in record

Question 5

What is comparative anatomy?

Answer 5

Examines anatomical structures of different living species to find similarities and differences

Question 6

How does comparative anatomy provide evidence for evolution?

Answer 6

• homologous structures are physical features in different species that have a similar underlying structure but may serve different functions
• organisms who share homologous structures likely evolved from common ancestor and have adapted structures for different functions
• homologous structures evidence for divergent evolution where organisms evolve different adaptive traits as they occupy new ecological niches

Question 7

What is comparative biochemistry?

Answer 7

Involves studying the molecular aspects of organisms to uncover evolutionary relationships

Question 8

What are useful biological molecules to study evolutionary links?

Answer 8

Cytochrome = highly conserved protein in cellular respiration so slight changes help identify evolutionary links

Ribosomal RNA = integral to protein synthesis so it changes slowly making it useful for showing connections between species that diverged long ago

Nuclear or mitochondrial DNA = species more closely related will have more similar DNA sequences

Messenger RNA = base sequences of mRNA are complementary to DNA so can assess DNA diversity

Amino acids = if closely related evolutionarily 2 species have more similar amino acid sequences because they are determined by mRNA and DNA

Question 9

What is the hypothesis of neutral evolution?

Answer 9

States most variability in molecule’s structure does not affect its function

Question 10

Why is neutral evolution useful in the study of evolution?

Answer 10

• ‘neutral’ changes that don’t affect function accumulate at regular rate as are not affected by natural selection
• comparing rates of neutral substitutions in molecular sequences of different species lets scientists estimate time since 2 species diverged from a common ancestor

Question 11

What is variation?

Answer 11

Difference observed among individuals within any given population

Question 12

What is genetic variation?

Answer 12

Variation due to genes and alleles an individual possesses

Question 13

What are sources of genetic variation?

Answer 13

Mutations = changes to genes and chromosome may be passed on to next generation

Meiosis = new combinations of alleles present in gametes formed produced by independent assortment and crossing over

Random fertilisation = random fertilisation of gametes produces new combinations of alleles in a zygote

Question 14

What environmental factors can cause variation?

Answer 14

• light
• nutrient and food availability
• temperature
• rainfall
• soil conditions
• pH

Question 15

What are polygenes?

Answer 15

Different genes at different loci that contribute to particular phenotype aspect producing observable variation

Question 16

What is continuous variation?

Answer 16

When there’s a range of values between 2 extremes without distinct categories producing a spectrum of phenotypes typically affected by both genes and environment

Question 17

What is discontinuous variation?

Answer 17

Features clear, distinct categories with no intermediates typically caused entirely by genes

Question 18

What is infraspecific variation and give an example?

Answer 18

Variations occurring within a species

e.g weight of robins can vary from 16 g to 22 g

Question 19

What is interspecific variation and give an example?

Answer 19

Variations occurring between different species

e.g bee hummingbird weighs about 1.6 g whereas ostrich weighs up to160 kg

Question 20

What equation is used to quantify variation?

Answer 20

Standard deviation

Question 21

What does standard deviation values tell us?

Answer 21

Smaller SD = fairly consistent values clustered around mean
Larger SD = fairly inconsistent values widely spread around mean

Question 22

What do the parts of the standard deviation equation mean?

Answer 22

∑= sum of
X = measured value
X ¯ = mean value
n = total number of values in sample

Question 23

What is a student’s T test?

Answer 23

Used to determine if there is significant difference between mean values of a particular variable across 2 populations

Question 24

What are the conditions required for using a T test?

Answer 24

• data must be continuous and normally distributed
• variances of populations should be equal
• samples must be independent of each other

Question 25

What do the parts of the T test equation mean?

Answer 25

X1 = mean of 1st dataset X2 = mean of 2nd dataset Q1 = SD of 1st data set Q2 = SD of 2nd dataset n1 = sample size of 1st dataset n2 = sample size of 2nd dataset

Question 26

How do you calculate degrees of freedom in a T test?

Answer 26

n1 + n2 - 2

Question 27

Describe what happens after you calculate df in a T test?

Answer 27

1) critical value determined by df and chosen significance level (usually 0.05) 2) If T statistic is greater than critical value reject null hypothesis as the means are significantly different 3) if T statistic is less than critical value accept null hypothesis as no significant difference between means due to chance