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.
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
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/Human_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