Topic 3:2 - comparative genomics

Question 1

What is comparative genomics?

Answer 1

Comparative genomics is a field of biological research in which researchers compare the genomes of organisms to identify regions of similarity and difference.

Question 2

What is evidence obtained from comparative genomics used for?

Answer 2

Evidence obtained is used to make inferences about the evolutionary relationships between organisms, as well as providing insight as to how the appearance, behaviour and biochemistry of living things have changed over time.

Question 3

What is the primary cause of variation in the genome of living things

Answer 3

Mutations. Spontaneous and induced mutations accumulate in genomes causing variation in the DNA sequence over time.

Question 4

Genetic variation can be observed by…

Answer 4

comparing the nucleotide base sequence of certain gene types that are present in all species that evolved from a common ancestor

Question 5

explain the importance of nucleotide sequences in protein synthesis

Answer 5

Genes have nucleotide sequences that are essential for the correct function of proteins. The specific sequence of nucleotides code for

Question 6

What is one piece of evidence for evolution of different genes (think nulceotide sequences)

Answer 6

The accumulation of mutations in non-essential nucleotide sequences provide scientists with evidence for the evolution of a gene.

Question 7

Explain how sequencing common proteins is another method of comparative genomics

Answer 7

Proteins are made of chains of amino acids, the sequence of amino acids are determined by nucleotide sequences in a section of DNA (gene). Hence, comparing the sequence of amino acids in proteins that are common between organisms will shed light on the similarity of their genes. The more differences there are in the amino acid sequence, the more differences there will be in the nucleotide sequence of the DNA.

Question 8

list techniques for comparative genomics

Answer 8

• DNA-DNA hybridisation
• protein sequencing
• DNA sequencing
• DNA profiling
• rRNA sequencing

Question 9

Define DNA-DNA hybridisation

Answer 9

DNA-DNA hybridisation is a technique of comparative genomics.

it is used to measure the degree of similarity between the DNA of two organisms.

Question 10

explain the steps to DNA-DNA hybridisation

Answer 10

1. DNA extraction. DNA is extracted from the different organisms using DNA extraction techniques.
2. The DNA from both organisms is heated separately to approximately 90 degrees to separate the weak hydrogen bonds between the nucleotide bases that hold the two strands of DNA together. This separates the strands to expose the nucleotide bases
3. The now single stranded DNA of both organisms is mixed together
4. The mixture of DNA is cooled to allow for hydrogen bonds to reform between complimentary base pairs. DNA of the different organisms will bond to form double helixes at sites where there are complimentary base sequences
5. The mixture is reheated to determine the separation temperature of the hybrid DNA. The higher the separation temperature, the higher the percentage of DNA-DNA hybridisation (more of the DNA was complimentary and hence more hydrogen bonds formed between bases, hence more heat energy is required to separate the strands). AND the lower the separation temperature, the lower the percentage of DNA-DNA hybridisation, as less of the DNA was complimentary so less complimentary base pairing occurred.

Question 11

What does a higher separation temperature indicate?

Answer 11

indicates greater similarity hence a more recent common ancestor.

Question 12

What does a lower separation temperature indicate?

Answer 12

indicates less similarity hence a less recent common ancestor.

Question 13

BRIEFLY describe DNA sequencing, and explain its importance in comparative genomics

Answer 13

DNA sequencing allows for researchers to observe the similarity of DNA between species to determine their relatedness.

• DNA is extracted from different organisms.
• DNA for a common gene is amplified using PCR.
• These genes are individually sequenced to determine the exact nucleotide sequence of each.
• Nucleotide sequences are compared between species.

Question 14

What do the results of DNA sequencing indicate in terms of comparative genomics? (how does the number of differences of DNA nucleotides relate?)

Answer 14

• Fewer differences indicate less time for mutations to occur hence a more recent common ancestor. Therefore, the species are more closely related.
• More differences indicated more time for mutations to occur hence a less recent common ancestor. Therefore, the species are less closely related.

Question 15

define rRNA sequencing and explain its importance in comparative genomics

Answer 15

Ribosomal RNA (rRNA) is a component of ribosomes present in cells of all organisms. This makes it ideal for comparing.

The genes that code for rRNA evolve very slowly and this property allows scientists to sequence genes for rRNA and compare the sequences to determine evolutionary relationships between organisms that diverged millions of years ago.

Question 16

define mtDNA and explain its importance in comparative genomics

Answer 16

mitochondrial DNA is DNA found in mitochondria of all cells.

MtDNA evolves rapidly and can be used to investigate relationships between groups that diverged more recently.

mtDNA is beneficial because it can be extracted from mitochondria in sufficient amounts for analysis without needing PCR as there are many mitochondria in each cell and many copies of the chromosome in each mitochondria.

Question 17

What is a phylogenic tree?

Answer 17

A phylogenetic tree is a diagram showing the inferred evolutionary relationships between individuals and groups of organisms based on similarities and differences in both genetic and physical features.

Question 18

What are mutations?

Answer 18

mutations are permanent inheritable changes in the nucleotide sequence of an organisms DNA. Mutations accumulate over time and are the ultimate source of genetic variation in a species.