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  1. Useful Genetics Professor Rosie Redfield The University of British Columbia This video is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported license.

  2. Lecture 1E • What’s a chromosome? ?? Outline: One very long DNA molecule Information for 100s or 1000s of genes Regulatory signals We each have 2 versions of each of 23 kinds Learning objectives: • Relate the physical and informational properties of chromosomes • Recognize different representations • Use gene, allele and locus correctly

  3. Chromosome structure: • One very long molecule of DNA. • (e.g. human X = 1.5 x 108 bp) • Bound to and wrapped around proteins • Chromosome information: • One very long DNA sequence. • Genes and other functions embedded in nonfunctional sequence.

  4. For a molecule of DNA to function as a chromosome, it must carry specific information: Signals recognized by DNA replication proteins (‘origins’ where DNA replication starts and ‘telomeres’ at the chromosome ends). A ‘centromere’ signal that creates an attachment point for the fibers that pull replicated chromosomes apart in cell division. (Genes)

  5. Human chromosomes are fairly typical: • 23 different ones (2 versions of each) • Named 1 to 22, from largest to smallest, and X and Y (the two versions of the ‘sex chromosomes’ • ~50 – 250 million base pairs long • ~400 – 4000 genes on each (Some unusual organisms encode all their genes in only a few very large chromosomes, and some have them in hundreds of tiny chromosomes.)

  6. How are genes arranged on the chromosomes? Not neatly! Not compactly!

  7. NM_080574 C20orf70: chromosome 20 open reading frame 70 Images from HapMap http://hapmap.ncbi.nlm.nih.gov/

  8. Question: Chromosome 20 is about 60 x 106 bp long and has about 900 genes. If all its genes are like the one highlighted below, how much of its DNA codes for protein? ~0.03% ~0.3% ~3% ~30% NM_080574 C20orf70: chromosome 20 open reading frame 70

  9. Essential terminology: locus, gene, allele LOCUS: the location of a gene or other DNA sequence on a chromosome. (refers to any/all alleles of that gene) ALLELE: a non-identical version of a gene or, more generally, of a DNA sequence. GENE: Usually, a segment of DNA specifying a protein or functional RNA. (Often used where ‘allele’ or ‘locus’ would be clearer.)

  10. How chromosomes are represented: Chromosomes are not shaped like blobby Xs or skinny butterflies. The bands drawn on chromosome ‘ideograms’ do not represent genes. How I will usually represent chromosomes

  11. How chromosomes are represented: Chromosomes are not shaped like blobby Xs or skinny butterflies. The bands drawn on chromosome ‘ideograms’ do not represent genes. How I will usually represent chromosomes

  12. What we’ve done The physical and informational content of chromosomes Regulatory signals control chromosome function How genes are ‘arranged’ on chromosomes terminology: origin, telomere, centromere, locus, allele How chromosomes are represented

  13. Coming up.... ? Lecture 1F • Life cycles and ploidy