Chromosomes and Diseases Genetics MBG-210. How many chromosomes in humans? Theophilus Painter in...
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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