DNA and the Genome, KA 5-8

Question 1

What is the genome?

Answer 1

The genome of an organism is its entire hereditary information encoded in DNA.

Question 2

What makes up a genome?

Answer 2

A genome is made up of genes and other DNA sequences that do not code for proteins.
Most of the eukaryotic genome consists of non-coding sequences.
DNA sequences that code for protein are defined as genes.
Other sequences regulate transcription and others are transcribed but never translated.
tRNA and rRNA are non-translated forms of RNA.

Question 3

What are mutations?

Answer 3

Mutations are changes in the DNA that can result in no protein or an altered protein being synthesised.

Question 4

Single gene mutations

Answer 4

Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of the substitution, insertion or deletion of nucleotides.
Nucleotide substitutions can result in missense, nonsense or splice-site mutations.
Nucleotide insertions or deletions result in frame-shift mutations.

Question 5

Missense mutations

Answer 5

Missense mutations result in one amino acid being changed for another.
This may result in a non-functional protein or have little effect on the protein.

Question 6

Nonsense mutations

Answer 6

Nonsense mutations result in a premature stop codon being produced which results in a shorter protein.

Question 7

Splice-site mutations

Answer 7

Splice-site mutations result in some introns being retained and/or some exons not being included in the mature transcript.

Question 8

Frame-shift mutations

Answer 8

Frame-shift mutations cause all of the codons and all of the amino acids after the mutation to be changed. This has a major effect on the structure of the protein produced.

Question 9

Chromosome structure mutations

Answer 9

Duplication is where a section of a chromosome is added from its homologous partner.
Deletion is where a section of a chromosome is removed.
Inversion is where a section of chromosome is reversed.
Translocation is where a section of a chromosome is added to a chromosome, not its homologous partner.
The substantial changes in chromosome mutations often make them lethal.

Question 10

Importance of gene duplication

Answer 10

Duplication allows potential beneficial mutations to occur in a duplicated gene whilst the original gene can still be expressed to produce its protein.

Question 11

What is evolution?

Answer 11

The changes in organisms over generations as a result of genomic variations.

Question 12

What is natural selection?

Answer 12

Natural selection is the non-random increase in frequency of DNA sequences that increase survival and the non-random reduction in the frequency of deleterious sequences.

Question 13

Types of selection

Answer 13

In stabilising selection, an average phenotype is selected for and extremes of the phenotype range are selected against.
In directional selection, one extreme of the phenotype range is selected for.
In disruptive selection, two or more phenotypes are selected for.

Question 14

What is vertical gene transfer?

Answer 14

Vertical gene transfer is where genes are transferred from parent to offspring as a result of sexual or asexual reproduction.

Question 15

What is horizontal gene transfer?

Answer 15

Horizontal gene transfer is where genes are transferred between individuals in the same generation.

Question 16

Why is natural selection more rapid in prokaryotes?

Answer 16

Prokaryotes can exchange genetic material horizontally, resulting in faster evolutionary change than in organisms that only use vertical transfer.

Question 17

What is a species?

Answer 17

A species is a group of organisms capable of interbreeding and producing fertile offspring, and which does not normally breed with other groups.

Question 18

What is speciation?

Answer 18

Speciation is the generation of new biological species by evolution as a result of isolation, mutation and selection.

Question 19

Isolation barriers

Answer 19

Isolation barriers are important in preventing gene flow between sub-populations during speciation.
Geographical barriers lead to allopatric speciation.
Behavioural or ecological barriers lead to sympatric speciation.

Question 20

Genomic sequencing

Answer 20

In genomic sequencing the sequence of nucleotide bases can be determined for individual genes and entire genomes.
Computer programs can be used to identify base sequences by looking for sequences similar to known genes.
Many genomes have been sequenced, particularly of disease-causing organisms, pest species and species that are important model organisms for research.

Question 21

What is phylogenetics?

Answer 21

Phylogenetics is the study of evolutionary history and relationships.

Question 22

What are sequence data and sequence divergence used for?

Answer 22

Sequence data is used to study the evolutionary relatedness among groups of organisms.
Sequence divergence is used to estimate time since lineages diverged.

Question 23

What are molecular clocks and how do they work?

Answer 23

Molecular clocks are used to show when species diverged during evolution.
They assume a constant mutation rate and show differences in DNA sequences or amino acid sequences.
Therefore, differences in sequence data between species indicate the time of divergence from a common ancestor.

Question 24

What provides evidence for the three domains of life?

Answer 24

Comparison of sequences provides evidence of the three domains of life: bacteria, archaea and eukaryotes.

Question 25

How can we determine the main sequence of events in evolution?

Answer 25

Evidence from phylogenetics and molecular clocks is used to determine the main sequence of events in evolution.
Use of sequence data and fossil evidence to determine the main sequence of events in evolution of life.

Question 26

What is the main sequence of events in the evolution of life?

Answer 26

Cells
Last universal ancestor
Prokaryotes
Photosynthetic organisms
Eukaryotes
Multicellularity
Animals 
Vertebrates
Land plants

Question 27

What is pharmacogenetics?

Answer 27

Pharmacogenetics is the use of genome information in the choice of drugs.

Question 28

Personal genomics

Answer 28

An individual’s genome can be analysed to predict the likelihood of developing certain diseases.
An individual’s personal genome sequence can be used to select the most effective drugs and dosage to treat their disease (personalised medicine).