Organisation of Eukaryotic Genomes

Question 1

What are the three genomes found in eukaryotic cells

Answer 1

1. Plastid genome – circular, ~130 genes, maternally inherited
2. Mitochondrial genome – circular, ~30–40 genes, maternally inherited, recombines within a cell
3. Nuclear genome – linear chromosomes, 25k–100k genes, biparentally inherited, highly variable in size

Question 2

What is the ‘three-parent baby’ technique used for

Answer 2

Replacing the nucleus in a donor egg to avoid mitochondrial disease transmission

Question 3

How is the genome measured

Answer 3

DAPI staining (fluorescence)
Completed genome base pair count

Question 4

What is the relationship between genome size and gene number

Answer 4

Weak correlation - larger genomes do not necessarily have more genes

Question 5

For which organism is a smaller genome advantageous

Answer 5

For parasites, due to energy/resource efficiency

Question 6

Typically range of protein-coding genes in eukaryotes

Answer 6

10,000–40,000 genes

Question 7

What influences gene number

Answer 7

Polyploidy increases gene count
Parasitic lifestyle may reduce gene count

Question 8

How long are typical genes and proteins

Answer 8

Gene length: 500–1000 bp (can be much larger)
Protein length: 100–1500 amino acids

Question 9

Why are genes >3x longer than their proteins

Answer 9

Due to UTRs and introns

Question 10

Can genes be found on both DNA strands

Answer 10

Yes

Question 11

What is the most abundant RNA in a cell

Answer 11

rRNA, ~80% of total RNA

Question 12

What is the role of rRNA repeat arrays

Answer 12

Multiple tandem copies improve production; intergenic spacers can be large

Question 13

What are ITS regions useful for

Answer 13

Phylogenetic studies – well-conserved, easy to amplify

Question 14

What does tRNA do and how is it made

Answer 14

Brings amino acids to ribosomes; made by RNA Pol III, ~15% of cellular RNA.

Question 15

What are snRNAs and snoRNA

Answer 15

snRNAs – Splicing (spliceosome components)
snoRNAs – RNA modification

Made by RNA Pol II/III

Question 16

What are small RNAs (miRNA, siRNA, piRNA) used for

Answer 16

Post-transcriptional gene regulation

Question 17

What is telomerase RNA

Answer 17

RNA component of telomerase, essential for telomere extension

Question 18

What are long non-coding RNAs (lncRNAs)

Answer 18

200nt long, often regulatory, tissue specific, antisense or intronic origin

Question 19

What are centromeres and what types exist

Answer 19

Monocentric – single centromere
Holocentric – centromeric regions scattered (no clear constriction)

Question 20

What are telomeres and their sequence motifs

Answer 20

Repetitive caps at chromosome ends (3–10 kbp TG-rich repeats)
Vertebrates: TTAGGG, Plants: TTTAGGG
Extended by telomerase

Question 21

What are satellite DNA and how are they identified

Answer 21

AT-rich repeats
Form satellite bands in CsCl gradients

Question 22

What causes expansion/contraction of repeats

Answer 22

DNA polymerase slippage
Imprecise repair

Question 23

How are microsatellites used in forensics

Answer 23

High individual variability makes them excellent genetic fingerprints

Question 24

What are the two main types of transposons

Answer 24

RNA-based (Retrotransposons) – Reverse transcribed from RNA, stay inserted

DNA-based – Excised and reinserted by transposase

Question 25

What roles do transposons play in evolution and genetics

Answer 25

Create genetic/epigenetic variation Induce chromosomal rearrangements Spread transcription factor binding sites Can be exapted into new genes