Unit 1 (KA7-8)

Question 1

Evolution

Answer 1

The gradual change in the characteristics of a population over time, as a result of natural selection working on genomic variation.

Question 2

Natural selection

Answer 2

The non-random process that increases the frequency of advantageous sequences, and decreases the frequency of deleterious sequences.

It allows the organisms that are best suited to their environment to survive, breed and pass on the alleles that give them an advantage.

Question 3

Deleterious sequences

Answer 3

Code for an inferior characteristic, which leave an individual poorly adapted to its environment.

These individuals fail to breed and pass on the sequence, which decreases in frequency and may disappear from the population.

Question 4

Normal distribution.

Answer 4

A bell-shaped curve showing an even distribution about the mean.

Many characteristics are controlled by several genes (polygenic inheritance) and show continuous variation across a range, from one extreme to the other, with most organisms being ‘average’.

Question 5

Stabilising selection

Answer 5

Intermediate phenotypes are favoured, and extremes are selected against, resulting in a decrease in genetic diversity and a narrowing of the normal distribution curve.

This tends to occur in a stable environment, where it is better to be ‘average’

eg. human birth mass

Question 6

Directional selection

Answer 6

One extreme phenotype is favoured, which pushes the mean in one direction.

Occurs in a period of environmental change.

eg. giraffe neck length, body mass of black bears in the ice age.

Question 7

Disruptive selection

Answer 7

Extreme phenotypes are favoured at the expense of intermediates.

Can result in the population being split into 2 distinct groups, and drives sympatric speciation.

eg. specialised beak shapes in the Galapagos finches.

Question 8

Phenotype frequency

Answer 8

How often different phenotypes (characteristics) occur in a population.

Question 9

Genetic drift

Answer 9

A random change in allele frequency.

Can affect rare alleles in small populations. if an allele is rare and the individual carrying it fails to breed, it may be lost from the population.

Question 10

Vertical inheritance (gene transfer)

Answer 10

The transfer of genetic sequences from parent to offspring as a result of sexual or asexual reproduction.

Question 11

Horizontal gene transfer

Answer 11

Genetic material is transferred from one cell to another, between members of a population and even between different species.

Transfer occurs within the same generation, and not from parent to offspring.

It allows prokaryotes to evolve very rapidly. eg. antibiotic resistance.

Question 12

Species

Answer 12

A group of genetically similar organisms that are able to breed to produce fertile offspring.

Question 13

Speciation

Answer 13

The formation of new species.

Occurs following the isolation of different groups within a population, which prevents exchange of genes.

Question 14

Allopatric speciation

Answer 14

The population is split by a geographical barrier, eg a mountain range or ocean.

The groups become isolated and are unable to exchange genes.

Random mutations in the separate groups are not shared, and natural selection acts differently on the separated populations.

Speciation has occurred if the groups can no longer breed to produce fertile offspring if reunited.

Question 15

Sympatric speciation

Answer 15

The population is split by an ecological or behavioural barrier, eg. different food sources, courtship behaviours.

The isolated groups no longer breed and exchange genes.

Mutations in the separated populations are not shared, and natural selection acts differently on the 2 groups.

Speciation has occurred if they fail to breed and produce fertile offspring if reunited.

Question 16

Genomic sequencing

Answer 16

Determining the base sequence for genes and for whole organisms.

Question 17

Bioinformatics

Answer 17

The use of molecular biology, statistics and computer technology to map and analyse DNA sequences.

Question 18

Genome shotgun approach

Answer 18

Used to sequence whole genomes.

The genome is copied many times and is broken into fragments using a mixture of restriction endonucleases which cut the DNA in different places.

Each fragment is sequenced, and the order of bases is worked out using a computer program that looks for overlaps.

Question 19

Restriction endonucleases

Answer 19

Enzymes that cut DNA at a specific short sequence (recognition site).

There are many different types which can cut DNA in different places, with different types of cuts. (eg. straight/staggered cuts).

Question 20

Sequenced genomes

Answer 20

Include humans, pest species (eg. mosquito), important foods (eg. rice) and model organisms (eg. fruit flies).

Question 21

Comparative genomics

Answer 21

Compares the sequenced genomes of different species, individuals of the same species or cells from the same individual. (eg. cancerous/non-cancerous).

Looks for similarities and differences to discover degree of relatedness or causes of disease.

Question 22

Highly conserved genes

Answer 22

These genes are very similar, with very few base differences, even though they come from different species.

They are often key genes eg. proteins involved in respiration, that have mutated very little (as any mutations would be fatal).

Question 23

Phylogenetics (molecular)

Answer 23

The study of evolutionary history and the relationships between groups of organisms, using genome sequence data.

It has advantages over comparison of structural features, as many closely related species look very different, whereas organisms that appear to be similar are unrelated.

Question 24

Phylogenetic tree

Answer 24

A diagram that shows evolutionary relationships, and how recently groups diverged from a common ancestor.

Divergence is estimated by looking at genome differences. Closely related species have similar genomes. The greater the difference, the larger the evolutionary distance between groups.

Question 25

Molecular clock

Answer 25

It is assumed that mutations accumulate at a steady rate over time.

The number of mutations that accumulate is proportional to the elapsed time since 2 groups diverged. ie. the more differences, the longer ago 2 groups of organisms diverged.

Base changes in DNA or amino acid differences in highly conserved genes can be used as molecular clocks.

Question 26

Fossil evidence

Answer 26

Used in combination with structural and genome sequence data to determine evolutionary relationships.

Question 27

Common ancestor

Answer 27

An ancestor that is shared between groups of organisms.

Found at the start of a phylogenetic tree, and at branch points where groups diverge.

Question 28

Domain

Answer 28

A group of living organisms.

There are 3 domains - bacteria, archaea (both prokaryotes) and eukaryotes.

Archaea branch off the eukaryote line, which diverged from the bacteria line.

Relationships were investigated using rRNA (highly conserved).

Question 29

Personal genomics

Answer 29

Sequencing an individual’s genome to predict the likelihood of genetic diseases or disorders.

Question 30

Pharmacogenetics (personalised medicine)

Answer 30

The use of genome information in the choice of drugs or dosages.

Question 31

Order of evolutionary events

Answer 31

Life appeared on Earth 4500 million years ago, followed by prokaryotes, eukaryotes, multicellular organisms, animals, vertebrates and then land plants.