LIFECYCLE OF A GENE

Question 1

What are the potential fates of duplicated genes?

Answer 1

Lost gene:

• Deletion (contraction)

-Genetic drift (by chance)

-Selection against

• Loss of function by mutation (pseudogenisation), where the start codon mutates, preventing transcription, resulting in a pseudogene.

Question 2

How are duplicated genes preserved?

Answer 2

Compensation

Neofunctionalization (new gene function)

Subfunctionalisation (temporal and specialization, such as different hemoglobin types expressed at different stages of development)

Lack of selection against or for the gene

Question 3

What does genome evolution involve?

Answer 3

Genome evolution includes gene gain and loss, showing divergence from the most recent common ancestor.

Question 4

Where do new genes come from?

Answer 4

Horizontal gene transfer (HGT): Genetic material from separate organisms

Duplication of an existing gene

De novo genes: Created from previously non-coding DNA

Question 5

What is horizontal gene transfer (HGT) and its significance?

Answer 5

HGT is more common in prokaryotes and involves exchanging genetic material between organisms that are not parent and offspring, often between species.

Significance: It plays a role in evolution, allowing adaptation for specific environments.

Question 6

What are the outcomes of horizontal gene transfer?

Answer 6

Spread of antibiotic resistance

Degradation of rare substances

Virulence

Question 7

What are the mechanisms of horizontal gene transfer?

Answer 7

1. Uptake from the environment (transformation)
2. Transfer from other bacteria (conjugation)

3.Injection by viruses (transduction)

Question 8

Can horizontal gene transfer occur in eukaryotes?

Answer 8

Yes, it can occur in eukaryotes through transfer of genes into nuclear genomes, such as endosymbiotic events like mitochondria and chloroplasts.

Question 9

What is the significance of endosymbiotic events for HGT?

Answer 9

Ancestors of mitochondria and chloroplasts had about 5000 genes. Over time, genes transferred from organelles into the genome caused a loss of genes in organelles.

Question 10

What is duplication, and how does it contribute to new genes in eukaryotes?

Answer 10

Duplication, the most common source of new genes in eukaryotes, can occur through duplication of the whole genome, chromosomes, or DNA segments.

Question 11

What is autopolyploidisation, and how does it relate to whole genome duplication?

Answer 11

Autopolyploidisation is an example of whole genome duplication, often involving a meiotic error that produces a diploid gamete, leading to aneuploidy

Question 12

How does hybridization contribute to gene duplication?

Answer 12

Duplication by hybridization occurs frequently in plants, producing offspring with significant adaptability.

Question 13

What are the mechanisms of DNA segment duplication?

Answer 13

Replication error

Unequal crossover

Retrotransposition

Question 14

What is required for the formation of de novo genes?

Answer 14

A sequence must acquire an open reading frame (ORF) and be transcribed by RNA Pol II to become a gene.

Question 15

What are transposable elements (TEs)?

Answer 15

TEs are sequences of DNA that can “jump” around in the genome, moving from one location to another.

Question 16

What are the two main classes of transposable elements (TEs)?

Answer 16

Class 1 (Retrotransposons): Copy-and-paste mechanism where a part of the element gets transcribed into RNA, reverse-transcribed back into DNA, and integrated into the genome. This duplicates the TE.

Class 2 (DNA transposons): Cut-and-paste mechanism where the element is excised from the donor DNA and integrated into a new target site, leaving a gap in the original location.

Question 17

How do Class 1 transposable elements (retrotransposons) work?

Answer 17

They use a copy-and-paste mechanism, where a part is transcribed into RNA, reverse-transcribed back into DNA, and then integrated into a new location in the genome, resulting in duplication.

Question 18

How do Class 2 transposable elements (DNA transposons) work?

Answer 18

They use a cut-and-paste mechanism, where the element is physically excised from the donor DNA and inserted into a new target DNA, leaving a gap at the original site.

Question 19

What happens to telomeres over time?

Answer 19

Telomeres shorten as time passes.

Question 20

What conditions are linked to the shortening of telomeres?

Answer 20

Aging

Cancer

Immune diseases

Cardiovascular diseases

Metabolic diseases

Psychiatric diseases

Question 21

What happens to transposable elements (TEs) in chromosomes over generations?

Answer 21

Chromosomes accumulate copies of TEs over generations unless there is strong selection against the copies or pseudogenisation occurs, making the TEs non-functional.

Question 22

What happens if a Class 1 transposable element (TE) is located before a gene?

Answer 22

Both the TE and the gene will be copied and pasted, potentially leading to gene duplication.

Question 23

How can you detect new genes formed by transposable elements (TEs)?

Answer 23

: If the introns are removed before reverse transcription and pasting into new DNA, the inserted DNA will not have any introns, indicating the formation of a new gene.

Question 24

What happens to most duplicated transposable elements (TEs) over time?

Answer 24

They usually mutate and lose their ability to duplicate, a process known as pseudogenisation. This can also happen if they move into other TEs and cause mutations, rendering them non-functional.