Linked Genes

1
How much DNA?
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Chromosomes
46 Chromosomes 23 homologous pairs
44 autosomes 2 sex chromosomes
Average chromosome length 4cm 120 base pairs
long contains thousands of genes
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Genes
Gene lengths vary from 8,000 - 2,000,000 base
pairs
Genome total set of genes in an organism
Human genome 30,000 - 40,000 genes
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Where do you find DNA?

• All mature cells contain DNA except the red blood
  cells
• DNA is found in the nucleus
• Small amounts of DNA are also present in the
  chloroplasts and mitochondria

• Source http//www.tokyo-med.ac.jp/genet/picts/cel
  l-e.jpg

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Mitochondrial DNA

• Represented as mtDNA
• Double-stranded circular molecule made up of
  16,568 base pairs, coding for 37 genes
• 13 genes code for proteins involved in cellular
  respiration
• 2 genes code for ribosomal RNA (rRNA)
• 22 genes code for transfer RNA (tRNA)

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Mitochondrial DNA
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Representing DNA
5A C G T T C G A A G C T A G G T T A T C G A3
If this represents the sequence of bases on one
strand of DNA, what would the sequence of the
other strand be?
3T G C _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ G C T5
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This is the principle used in gene-sequencing
DNA sample is heated to separate strands forming
a template
5A C G T T C G A A G C T A G G T T A T C G A3
Nucleotides are added to the mix with each of the
4 DNA bases. Additional fluorescent dye-labelled
nucleotides are also added to the mix
The mixture is cooled allowing the added
nucleotides to attach to the template strand
according to base-pair rules
A C G T T C G A A G C T A G G T T A T C G A
T
Varying lengths of complementary strands are
produced. At the end of each strand, a nucleotide
with the fluorescent dye attaches, causing the
synthesis of the strand to stop
T G
T G C
The dyes are detected by an electronic analyser
which records the result
T G C A
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Human Genome Project

• This technique of DNA sequencing has made it
  possible for scientists to collaboratively map
  the entire Human Genome
• Began in 1990 and fully completed in 2003
• Aims
• Improve diagnosis of genetically inherited
  disorders
• Improve treatments for a range of diseases
• Prevent diseases that have a genetic
  predisposition

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Interesting facts about the Human Genome
Two unrelated humans will share 99.9 of their
total DNA
The differences between individuals are
called single nucleotide polymorphisms
95 of human DNA function is unknown and referred
to as 'junk'
2,850,000,000 base pairs long
Genes only make up 1.5 of total genome
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Flanking regions
Coding Region
Upstream Flanking Region
Downstream Flanking Region
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Comparative Genomics

• The sequences of many other genomes have been
  sequenced
• This allows scientists to compare the genomes of
  a variety of species and determine degrees of
  relatedness between them