L15: Genome Evolution & Multigene Families

Question 1

What are syntenic genes?

Answer 1

Genes that are grouped in the same way on the chromosomes of two (or more) species

Question 2

What are syntenic blocks?

Answer 2

Regions containing the homologous genes

Question 3

How are chromosomal rearrangements defined?

Answer 3

By looking for blocks of synteny between chromosomes of different organsims

Question 4

What is an example of chromosome rearrangement?

Answer 4

Translocation

Question 5

What disease is an example of rearrangement of chromosomes?

Answer 5

Acute Myelogenous Leukaemia

Question 6

What are the rearrangements that take place in Acute Myelogenous Leukaemia?

Answer 6

Translocations and inversions

Question 7

What is centric fusion and Robertsonian translocation of chromosomes?

Answer 7

2 telocentric chromosomes fuse to generate 1 new chromosome, short arms lost so individual only has 45 chromosomes

Question 8

What are the consequences of centric fusion and Robertsonian translocation?

Answer 8

• If no essential material in short arms no phenotype is produced
• After meiosis may generate trisomy or monosomy of long arms
• eg down syndrome & patau syndrome

Question 9

Why do the chromosomes have bands on them?

Answer 9

The stain is used to clearly discriminate different chromosomes/regions of them

Question 10

How can inversion of chromosomes take place?

Answer 10

As they may be paracentric in one or both arms

Question 11

How do changes to genomes occur?

Answer 11

Mainly through accidents or mistakes

Question 12

In what processes do accidents/mistakes occur?

Answer 12

DNA replication, recombination & repair leading to simple/complex changes (point mutation, translocations, deletions, duplications & inversions)

Question 13

How is the genome made more complex?

Answer 13

-Small scale gene duplications
-Large scale gene duplications followed by loss of superfluous genes and divergence of the retained homologues

Question 14

What is sister chromatid exchange?

Answer 14

-2 pairs of sister chromatids line up during meiosis. A repetitive region of one chromatid (the third one) does not line up exactly with corresponding region in others
- Strand breaks on non-sister chromatids result in unequal crossover, and different number of repeat units
- Strand breaks on sister chromatids also produce different repeat numbers

Question 15

What is an example of an organism that has gone through genome duplication?

Answer 15

S. cerevisae

Question 16

What are the benefits of genome duplication?

Answer 16

The extra set of genes do not have the same restriction on mutation rate as a single copy

Question 17

What are multigene families?

Answer 17

Arise after duplication events and are followed by mutation to generate alteration in expression/function

Question 18

What are homeotic (hox) genes?

Answer 18

The proteins encoded by hox genes are transcription factors that influence expression patterns of many genes during development

Question 19

What are examples of hox genes?

Answer 19

bithorax, Antennapedia and Ultrabithorax in Drosophila

Question 20

How does the position of the gene influence the expression?

Answer 20

The gene can be located in a specific segment which when expressed are located in that area (eg genes for wings are located in a specific segment)

Question 21

How does mutation of a hox gene lead to changes in segmental identity?

Answer 21

Altered expression of downstream targets i.e. genes for which the hox protein is a transcription factor

Question 22

Which chromosome are the 6 beta globin genes location on?

Answer 22

Chromosome 11

Question 23

Where is the expression of beta globins?

Answer 23

Epsilon - During embryogenesis
Gamma - during fetal development
Beta - switch from gamma at around time of birth
Delta - low level expression in children & adults

Question 24

Where is the expression of alpha globins?

Answer 24

Xi - fist few weeks of embryogenesis the alpha

Question 25

What is Thalassemia?

Answer 25

Unbalanced production of globins which results in abnormal hemoglobin

Question 26

How does Thalassemia take place and what measures the severity?

Answer 26

Result from mutations in either alpha or beta and severity depends on how many genes are affected and how severe the mutations are

Question 27

What is Beta Thalassemia?

Answer 27

Impacts 2 beta genes if both mutated - major (death by ~20 years), if 1 mutated - asymptomatic
Excess alpha chains do not tetramerise so they bind to RBC membrane and can aggregate

Question 28

What are other examples of hox mutations?

Answer 28

Exon shuffling - exons corresponding to discrete domains
De novo generation of genes - when a gene is neutral or advantages the gene is retained as a new gene