Chromosomes and Diseases

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Chromosomes and Diseases

• Genetics MBG-210

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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.

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Chromosome 2 Humans, chimps, gorillas, and
orangutans
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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

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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.
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Evidence 1

• Chromosomes 2p and 2q, when laid end to end,
  create an identical banding structure with the
  human chr. 2.

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Evidence 2

• The remains of telomeres is found in the middle
  of human chromosome 2 where the ancestral
  chromosomes fused.

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Evidence 3

• the centromere of human chromosome 2 lines up
  with the chimp chromosome 2p chromosomal
  centromere.

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Evidence 4

• At the place where we would expect it on the
  human chromosome we find the remnants of the
  chimp 2q centromere

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Are humans more closely related to chimps than
they are to gorillas?
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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.

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Gene Gateway

• http//www.ornl.gov/sci/techresources/Human_Genome
  /posters/chromosome/

http//www.ornl.gov/sci/techresources/Human_Genome
/posters/chromosome/chooser.shtml
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Chromosome 2

• BRCA1-associate ring domain (breast cancer)
• Liver cancer oncogone
• Muscular dystrophy
• Orofacial cleft

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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.

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Go to Genes and disease, and select a chromosome
http//www.ncbi.nlm.nih.gov/disease/chr9-12.html