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Chromosomes and Diseases
Genetics MBG-210
How many chromosomes in
humans?
• Theophilus Painter in 1921 characterized
the number of chromosomes as 24 on
spermatocytes. Others repeated the
experiment and somehow came up with the
same conclusion.
• Until 1955, it was agreed that humans have
24 pairs of chromosomes!!!
– With better techniques, the number came down
to 23 pairs.
Chromosome 2: Humans,
chimps, gorillas, and orangutans
Hypothesis
• Observation: Chimps, gorillas, and
orangutans have 24 pairs of chromosomes,
whereas humans have 23 pairs.
• Hypothesis: Common ancestor of all great
apes had 24 pairs of chromosomes and that
the fusion of two of the ancestor's
chromosomes (chromosomes 2p and 2q)
created chromosome 2 in humans
http://www.evolutionpages.com/chromosome_2.htm
Telomere: a sequence of DNA at the
end of the chromosome whose
function is to protect the ends of the
chromosomal DNA strands during
replication.
Centromere: seen on a condensed
chromosome as a pinched region,
contains proteins which form
kinetochores to attach the sister
chromatids.
Evidence 1
• Chromosomes 2p
and 2q, when laid
end to end, create
an identical
banding structure
with the human
chr. 2.
Evidence 2
• The remains of
telomeres is found in
the middle of human
chromosome 2
where the ancestral
chromosomes fused.
Evidence 3
• the centromere of
human chromosome
2 lines up with the
chimp chromosome
2p chromosomal
centromere.
Evidence 4
• At the place
where we would
expect it on the
human
chromosome we
find the remnants
of the chimp 2q
centromere
Are humans more closely related
to chimps than they are to
gorillas?
How related are chimps and
humans?
• Apart from the fusion in chr. 2, the 13 other
chromosomes no visible differences exist.
• 98% of the chimp and human genome are
identical.
• Although we look rather different from chimps
when we compare ourselves to amoebae (called an
outgroup in phylogenetic analysis) or even worms,
chimps and humans look alike.
Gene Gateway
• http://www.ornl.gov/sci/techresources/Hum
an_Genome/posters/chromosome/
http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/chooser.shtml
Chromosome 2
• BRCA1-associate ring
domain (breast cancer)
• Liver cancer oncogone
• Muscular dystrophy
• Orofacial cleft
Select a disease on a
chromosome
• Go to the website www.genetests.org
– On this page select geneReviews on the bar and
search for the disease name/keyword.
Go to Genes and disease, and
select a chromosome
http://www.ncbi.nlm.nih.gov/disease/chr9-12.html