Genes and Genomes

Question 1

Definition of a genome.

Answer 1

The totality of genetic information belonging to a cell/organism (particularly the DNA that carries this info).

Question 2

What is a chromosome?

Answer 2

The entire complement of genetic material in a chromosome set. Chromosome set = 1 copy of each unique chromosome.

Question 3

What is the chromosome composition for females?

Answer 3

22 autosomes + X chromosome.

Question 4

What is the chromosome composition for males?

Answer 4

22 autosomes + X + Y chromosomes.

Question 5

True or false: Females have more DNA, males have bigger genomes.

Answer 5

True

Question 6

Explain the C-value paradox.

Answer 6

C-value paradox = general trend of bigger genomes in more complex organisms, not a very good correlation.

Question 7

Genetic diversity between species.

Answer 7

Diff orgs have diff genome sizes, etc. C-value paradox = that bigger orgs have bigger genomes. This is contested with the drosiphilia (fly) that has a MASSIVE genome.

Question 8

What the definition of a gene?

Answer 8

Region of DNA transcribed as a single unit.

Question 9

What is the function of a gene?

Answer 9

• Carries information for a discrete hereditary characteristic.
• Corresponds to a single protein/single functional RNA (gene products).
• Requires a promoter/some kind of regulatory DNA as a part of the gene.

Question 10

Compare Prokaryotic and Eukaryotic Genes:

Answer 10

Prokaryotic:
- more simple.
- transcription and then translation.
- can have polycistronic genes with multiple gene products.

Eukaryotes:
- primary transcript
- 5’ capping
- RNA splicing
- 3’ polyadenylation
- exportation from nucleus into the cytoplasm
- translation

Question 11

Define the term ‘exon’.

Answer 11

Expressed gene sequences.
Parts of the gene that are expressed/present in the FINAL, mature RNA form.

Question 12

Define the term ‘intron’.

Answer 12

Intervening sequences.
Parts of a gene that are removed by splicing.

Question 13

What are the two types of pseudogenes?

Answer 13

1. Conventional
2. Processed

Question 14

Describe what a conventional pseudogene is. Use an example.

Answer 14

• B-globin is an example.
• Gene duplication occurs, creating two copies of the B-globin gene.
• 1st B-globin gene is still functioning. Therefore, the 2nd B-globin gene can undergo changes/mutations WITHOUT selection.
• Mutations affect promoter (affecting expression), coding sequence (e.g. nonsense and missense mutations), splicing sites, etc.
• Dysfunctional copy = pseudogene.

Question 15

Explain what processed pseudogenes are.

Answer 15

• Processed pseudogenes = no longer have introns.
• Reverse transcriptase makes DNA copy of mRNA instead of the original a DNA.
• Double-stranded DNA version inserts somewhere else in the genome.
• Processed pseudogene = non-functional.

Question 16

What are gene fragments?

Answer 16

Non-functional genes are broken up by chromosomal rearrangements into gene fragments.

Question 17

Are pseudogenes common or uncommon?

Answer 17

Common throughout the genome.

Question 18

What are the two different types of repetitive elements?

Answer 18

1. Tandem repeats.
2. Transposons.

Question 19

What are tandem repeats?

Answer 19

• repeated end to end copies of short DNA sequences.

Question 20

What two components make up Tandem Repeats?

Answer 20

1. Microsatellites: tandem repeats of very short (1.6 bp) DNA sequence total array size approx. 10-150 bp. Known as: Short Tandem Repeats/Simple Sequence Repeats.
2. Minisatellites: tandem repeats of short (7-100 bp) DNA sequence total array size approx. 100-20,000 bp.

Question 21

What are transposons?

Answer 21

• Known as Jumping Genes!
• Parasitic genetic elements that can move about the genome.

Question 22

What are the two types of transposition?

Answer 22

1. Conservative Transposition (cut and paste).
   - Transposons excised from the original position (leaving a characteristic mark) and inserted at a new location.
   - DNA transposons move conservatively.
2. Replicative Transposition (copy and paste).
   - Transposon inserts at a new location, BUT, an original copy remains.
   - Retrotransposons move replicatively.

Question 23

Can transposons cause disease? Provide two examples.

Answer 23

If a transposon inserts into a gene – affect the genes expression.

Example:
Haemophilia –> insertion of the retrotransposon L1 into the factor IX gene.
Muscular dystrophy –> L1 insertion into the dystrophin gene.

Question 24

Explain the movement process of DNA transposons.

Answer 24

1. Transposase gene transcribed and translated to make transposase protein.
2. Transposase enzyme binds to the ITRs (inverted terminal repeats).
3. Transposase enzyme catalyses excision of the DNA transposon from original site.
4. Transposons moves and recognises specific sequence and the transposase enzyme catalyses the insertion of the transposon into a new site (into the TSD).

Question 25

Explain the movement process of retrotransposons.

Answer 25

1. Retrotransposon transcribed into RNA (encodes reverse transcriptase enzyme).
2. Translation creates reverse transcriptase.
3. Reverse transcriptase synthesises reverse strand (in DNA) using RNA as template.
4. 2nd DNA stand is produced
5. Retrotransposon inserts into new chromosomal position.

Question 26

What are SINEs, LINEs, and LTR retrotransposon’s?

Answer 26

• SINEs = short, interspersed elements - 1.6 million total > 1 million Alu.
• LINEs = long interspersed elements - 900,000 total, 516,000 L1.
• LTR retrotransposon = long terminal repeat (like a retrovirus e.g. HIV - 8,000 total).