CSB349H1 Lecture Notes - Lecture 2: Copy-Number Variation, Fetal Hemoglobin, Gene Duplication
14 May 2018
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Lecture 2(a): Genes & Genome Structure
Where Do Genes Come From?
• Genes come from other genes; the major source of genes in our genome is:
1. Gene duplication
2. Divergence:
§ Occurs when an copies of genes are made – the copies will accumulate genetic
differences, therefore, the genes will become more variable over time
ð Gene duplication via retro-transposition:
o Retroviruses make RNA copies of themselves and copies it into
DNA and insert modified DNA in our genome
§ Retro-transposition is when a human gene (not a virus)
follows the same mechanism to duplicate (i.e. CDC14B)
• CDC14B must have made an mRNA copy, which was later translated
back into DNA – that DNA was inserted in another region in the human genome making us
have two copies
o What happened: virus in the process of converting it’s RNA into DNA to insert back
into our genome; but by accident the viral machinery used the RNA of human
§ Original copy (chromosome 9) consist of introns and exons with the possibility
of generating more than one mRNA (alternative splicing)
§ However the second copy (chromosome 7) does not have introns and only one
of the alternatively spliced exons
• Structure of the gene in DNA corresponds exactly to the structure of
the mRNA; therefore the gene was formed via copy of mRNA
ð Genes can duplicate via several mechanisms; retro-transposition is rare – most common are
mechanisms that create copy number variation (errors in recombination)
Gene Duplication With & Without Divergence:
• Tandem duplication – error that arises in recombination, what happens to the gene?
o Most often what happens is that one copy of the gene gets degraded –no longer
consider it a ‘duplication’
• If both copies of the genes are retained, the following may occur:
a) Selective Pressure on both Genes:
§ Both genes remain similar; no variation
b) Selective Pressure on one Gene:
§ One of the genes will acquire a new
function due to mutations
(neofunctionalization)
ð Subfunctionalization is what usually occurs:
o Function of the original gene is split up between the 2; each is specialized in one thing
Document Summary
Lecture 2(a): genes & genome structure: genes come from other genes; the major source of genes in our genome is, gene duplication, divergence: Occurs when an copies of genes are made the copies will accumulate genetic differences, therefore, the genes will become more variable over time. Gene duplication via retro-transposition: retroviruses make rna copies of themselves and copies it into. Dna and insert modified dna in our genome. Original copy (chromosome 9) consist of introns and exons with the possibility of generating more than one mrna (alternative splicing) Genes can duplicate via several mechanisms; retro-transposition is rare most common are mechanisms that create copy number variation (errors in recombination) Gene duplication with & without divergence: tandem duplication error that arises in recombination, what happens to the gene, most often what happens is that one copy of the gene gets degraded no longer consider it a duplication".
