Hox genes, Patterning and Evolution - Lecture 19

Question 1

What are homeotic mutations?

Answer 1

○ Transformation of one body part into another
○ Legs instead of antennae or wings instead of halteres

Question 2

What are hox genes?

Answer 2

○ First identified in drosophila causing homeotic transformations
○ Evolutionary conserved
○ Transcription factors: regulates the expression of other genes
○ Homeodomain: 60 aa helix-turn-helix DNA binding motif
○ Found clustered in genome

Question 3

What is tandem duplication?

Answer 3

○ Unequal cross-over caused by chromosome mis-pairing at meiosis, possibly caused by repeat DNA sequences
○ Gives rise to subfunctionalisation: duplicated genes can mutate without causing issues

Question 4

What can subfunctionalisation give rise to?

Answer 4

○ Change protein sequence
○ Change time/place of expression

Question 5

What is segmental duplication?

Answer 5

Duplicating groups of genes

Question 6

What gives rise to hox clusters?

Answer 6

Tandem and segmental gene duplication

Question 7

How do mammals have 4 hox gene clusters?

Answer 7

From whole gene duplication events

Question 8

How do whole gene duplication events happen?

Answer 8

○ Allotetraploidy = hybridisation between two separate species
○ Autotetraploidy = duplication of genome through improper meiosis within the same species

Question 9

How many hox genes are in mouse and humans?

Answer 9

○ 39 hox genes
○ Four clusters on four chromosomes
○ There are 13 paralogous groups

Question 10

How did experiments show that hox genes related to segmentation?

Answer 10

○ Mutations in specific hox genes
○ Hox10 paralogues mutants: all lumbar vertebrae are transformed to thoracic vertebrae
○ Hox11 paralogues mutants: all sacral vertebrae aare transformed to lumbar vertebrae