CSB349H1 Lecture Notes - Lecture 2: Gene Duplication, Hox Gene, Function Type
14 May 2018
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Lecture 2(b): Genes & Genome Structure
Hoc Gene Cluster:
• Evolution of the Hox gene cluster – duplication of an entire cluster
o Has occurred at least 3 times over evolutionary history
(entire cluster: group of genes was duplicated)
Distal-less Gene:
• Distribution of the gene in different species is extremely variable:
o 1 in Drosophila | 1 in C. Elegans
2 in Sea Squirt: genes are facing each other
ð Arrows indicate the direction of transcription
o Original duplication is presumed to have occurred
in the Sea Squirt
§ Within mice, the 2 copies were duplicated
3 more times because it seen that the
genes are organized the same way in
the chromosome
• This is another example where the
subfunctionalization has to do with where it is expressed:
o Much of the gene sequences have been conserved among the Dlx paralogs, however,
their expression profiles have diverged considerably
§ Different tissues during development will express different forms of the gene
* This example shows gene duplication and divergence of gene expression: where in the embryo
Duplication Degeneration Complementation (DDC) Model:
• Model that predicts that the changes in expression of duplicate genes is due to the
complimentary loss of region specific regulatory sequences
• Allowed for the partitioning of ancestral gene function – type of subfunctionalization
Example:
• Dlx ancestral gene was expressed in two areas: brain + body (hypothetically)
o Once the gene duplicates, we will have two copies and through the process of
evolution one of the genes may abrupt their function and no longer express in a
specific region (i.e. brain)
§ Therefore, the other copy is now essential because it will only be the one
functioning to express in the brain
ð Divergence of function – subfunctionalization:
o Require expression in two regions (brain, body); one gene functions to express in the
brain, while the other gene functions to express in the body (expression divergence)
ð Duplication degeneration:
o Expressing in the brain is degenerated by one copy of the gene
o Expressing in the body is degenerated by the other copy of the gene
