Genomes

Question 1

What is a DNA promotor sequence?

Answer 1

A sequence of DNA to which transcription apparatus binds to initiate transcription. It indicates direction of trancription and which of the 2 DNA strands are read as a template.

Question 2

What are introns and exons?

Answer 2

Eukaryotic genes have stretches of coding and non-coding nucleotides. The coding strands are called exons and the non-coding strands are called introns.

Question 3

How are introns and exons different in more complex organisms?

Answer 3

In eukaryotic genomes the size and number of introns appear directly related to organism complexity.

Question 4

What happens to percentage of genome that is non-coding with increasing complexity of the organism?

Answer 4

It increases

Question 5

What makes up the repetitive DNA sequences?

Answer 5

Repetitive DNA that includes transposable elements and related sequences. 44%

Repetitive DNA unrelated to transposable elements. 14%

Question 6

What are pseudogenes?

Answer 6

Genes that are no longer functional that result from duplication of genes with normal function but have accumulated too many deleterious mutations.

Question 7

How many genes are there in the human genome?

Answer 7

19 - 20k

Question 8

What is the largest gene in the human genome?

Answer 8

Dystrophin which is 2.4Mb long

Question 9

How are proteins arranged?

Answer 9

Into families

Question 10

How are relationships between proteins determined?

Answer 10

By comparing amino acid sequences; more similar sequences cluster on the same branches of the evolutionary tree.. Protein functionality can be reflected in the clustering.

Question 11

What are the 2 classes of homologous molecules?

Answer 11

Paralogs: Homologous sequences that are present within the same genome but often differ in biochemical functions.

Orthologs are homologs present in different species but often retain similar function through evolution.

Question 12

What does homology tell us?

Answer 12

It can give us more information about evolutionary history and function.

Homology between protein of unknown function and one that is known gives information about unknown protein’s function.

Question 13

What are repeats?

Answer 13

Repeated units of DNA that are 1 - 200 bp long

Question 14

What are transposable elements?

Answer 14

Pieces of DNA that have the ability to jump from place to place in the genome.

Question 15

Why do pseudogenes exist?

Answer 15

They can exist because a single functioning copy of a gene is sufficient

Question 16

What parts of normal genes do pseudogenes lack? What does this tell us?

Answer 16

They lack a promoter and introns.

This tells us they are believed to derive from mRNA copy reverse transcribed into cDNA and reintroduced into the genome.

Question 17

Which enzyme are pseudogenes believed to have been made from?

Answer 17

Reverse transcriptase from transposons

Question 18

How are processed pseudogenes believed to have been created?

Answer 18

Transcription and processing of RNA.

Reverse transcription to cDNA

Integration of cDNA into chromosomal DNA

Second-strand synthesis and DNA repair

Question 19

How are inactive pseudogenes named?

Answer 19

A Ψ symbol is put before the name.

Question 20

Where are alpha globin genes located for haemoglobin?

Answer 20

Chromosome 16

Question 21

Where are beta globin genes located for haemoglobin?

Answer 21

Chromosome 11

Question 22

Why are alpha and beta chains of haemoglobin on separate chromosomes?

Answer 22

They started off together as duplicate genes and then must have been transposed to different locations in the genome.

Question 23

What is the function of pseudogenes thought to be?

Answer 23

Regulation of gene expression

Question 24

What are minisatellites?

Answer 24

Repeat sequences of 7 - 100 bp long which are highly variable in length.

They can be in coding or non-coding regions and can affect gene regulation.

Question 25

How many minisatellites are in the human genome?

Answer 25

> 1000

Question 26

What is another name for minisatellites?

Answer 26

VNTRs

Question 27

What are microsatellites?

Answer 27

Tandem repeats of 1 - 6 bps

Question 28

What is another name for microsatellites?

Answer 28

Simple Sequence Repeats

Question 29

What is replication slippage?

Answer 29

Sometimes coding and replicating strand can slide apart and then come together again but in a misaligned way resulting in some sequences being replicated again.

Question 30

What is the result of replication slippage?

Answer 30

Expansion and contraction of repeat number can occur during DNA replication

Question 31

What are some diseases that are caused by trinucleotide repeat expansion?

Answer 31

Huntington’s disease

Fragile X syndrome

Myotonic dystrophy

Question 32

How many diseases are caused by mutations involving CGG, GCC, GAA, CTG, and CAG?

Answer 32

14 diseases (these mutations are found in coding and non-coding regions)

Question 33

What causes huntington’s disease?

Answer 33

Expansion of CAG (Glutamine codon) repeats in the coding region of huntingtin gene.

CAG repeats are translated into polyglutamine tract (6 - 35 repeats cause no disease. 36 - 121 repeats cause huntington’s disease. >70 repeats cause juvenile onset huntington’s disease).

Question 34

What is huntington’s disease characterized by?

Answer 34

Midlife onset of dementia followed by death

Question 35

What is a polyglutamine tract?

Answer 35

A sequence of glutamine residues produced due to the repeats.

Question 36

What are transposable elements?

Answer 36

DNA sequence that can change its position in the genome.