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Lecture 14

BIOLOGY 1M03 Lecture Notes - Lecture 14: Hox Gene, Gene Duplication, Hoxd13


Department
Biology
Course Code
BIOLOGY 1M03
Professor
Ben Evans
Lecture
14

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Biology 1M03 Lecture 14
Evolutionary development
Increased complexity does not necessarily involve large changes in gene number
o Frequently involves changes in gene expression
Those changes can occur in space and developmental time
Results suggest that major differences between species are not because there are different (or
more) genes, but instead because the same conserved genes are expressed in different ways
Genetic Toolkit
Many organisms have a conserved set of genes that are deployed developmentally by evolution to
carry out similar functions across closely related organisms
Similar genes (tools) are used in different ways to orchestrate a myriad of morphologies
Differences among species in how the tools in the toolkit are deployed lead to variation in body
plan and the number, identity, and pattern of body parts
Hox Genes in Humans
Humans have 39 Hox genes organized into 4 clusters
These genes have major roles in development of the central nervous system, axial skeleton,
gastrointestinal and urogenital tracts, external genitalia, limbs and digits
Mutation of many Hox genes cause lethality
o Some Hox gene mutations, such as Hoxd13, can cause developmental anomalies such as
polydactyly and synpolydactyly
o Truncation mutations in HoxA1, when homologous, disrupt development of the brainstem,
inner ear, and cardiovascular system, resulting in mental retardation and autism
o Mutations in HoxA13, affect development of fingers, toes, and uterus
Gene and Genome Duplication
One mechanism is through small scale duplication, where one gene becomes two and this
duplication happens on the same chromosome in the case of the Hox gene
How did copy number of Hox Genes change?
o Gene duplication
One gene becomes two and that duplication happens on the same chromosome in the
case of the Hox Genes
o Genome duplication
Duplicating the entirety of our genome
When a gene duplicates, a protein duplicates and the most common function of a duplication is
nonfunctionalization, where there's a mutation that happens in one or another copy that
inactivates that gene, end up with a non-functional copy (sometimes called a pseudogene) and a
functional ancestral copy
Redundancy is that it can be good to have two copies and natural selection may favour the
functional persistence of two tools
Neofunctionalization is that one copy receives mutations that confer some sort of novel function
o The new function is beneficial and natural selection will favour this persistence including the
one that has a novel function
Subfunctionalization situation where you have mutations that degrade functions of each copy
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