Genome Structure 1

Question 1

How are comparisons of genome size made?

Answer 1

At the haploid level.

Question 2

Give reasons why genome size doesn’t necessarily correspond to complexity.

Answer 2

Humans have a smaller haploid genome than some species. There are large differences in genome size between organisms with the same body plan and metabolism.

Question 3

Give evidence that more non-coding DNA results in more complexity.

Answer 3

Susumu Ohno showed that there were a limited number of functional gene loci, and after this there would be too much coding DNA, which would be detrimental to the organism. Puffer fish has a high amount of non-coding DNA that it doesn’t not require, but does not remove as this would require a high amount of energy.

Question 4

How can an increase in complexity be explained when there is more non-coding DNA?

Answer 4

Eukaryotes have sophisticated gene regulation systems, approx. 9% of genes code for transcription factors.Splicing and alternative splicing also increase complexity.

Question 5

How is the complexity of DNA defined?

Answer 5

The number of unique sequences present in a genome.

Question 6

What are the 3 types of DNA found in a eukaryotic genome?

Answer 6

Highly repetitive, Moderately repetitive and single/low copy.

Question 7

What type of sequences renature first?

Answer 7

Highly repetitive DNA.

Question 8

Where in a chromosome is there a low frequency of genes?

Answer 8

At the centromere.

Question 9

What are pseudogenes?

Answer 9

Genes where mutations have occurred that knock out the gene function.

Question 10

What are retrogenes?

Answer 10

Reactivated pseudogenes.

Question 11

What are multigene families?

Answer 11

Groups of identical or similar sequences, that can be tandemly arranged differently in different organisms.

Question 12

What is a complex gene family? Give an example.

Answer 12

Genes that have diverged from each other despite being tandemly arranged, e.g. the β globin gene.

Question 13

What is a dispersed gene family? Give an example.

Answer 13

Genes that have not been tandemly arranged but have become dispersed at several locations in the genome as a result of chromosomal rearrangements, e.g. the aldolase gene family with genes located on 5 chromosomes.

Question 14

What is spacer DNA?

Answer 14

Intergenic DNA with non-sequence specific functions.

Question 15

What are the roles of spacer DNA?

Answer 15

Allows for the flexibility of the 3D structure of DNA. Allows for transcription factor binding sites. Allows for complex regulatory mechanisms.

Question 16

What are telomeres?

Answer 16

Protective terminal regions of a chromosome that get shorter as organisms get older.

Question 17

What do telomeres consist of?

Answer 17

A repeated sequence.

Question 18

Why are telomeres needed?

Answer 18

To distinguish between real chromosome ends and double stranded breaks within a chromosome that needs fixing.

Question 19

What are hotspots?

Answer 19

Regions of the genome that are more prone to mutation.

Question 20

What evidence suggests that mutations are random and not at hotspots?

Answer 20

Mutations are not uniformly distributed in the genome. Mutations can only be recovered if the function is also recovered. Therefore mutations at cold spots must still occur but not affect function (are silent).