Transcript Document
DNA According to Watson & Crick (1953) Information is in the sequence of steps A G C T T G G A T C A A G C DNA Gene Chromosome Protein Chromosomes, cells, and people Meiosis Meiosis Problems with cell division: Down Syndrome Chromosome 21 Problems with cell division: Cancer At least 5 mutations Normal Cell Cancer Cell Obeys strict rules Divides only when told to Dies rather than misbehaving Stays close to home Disobeys rules Divides at will Bad behavior doesn’t kill Wanders through body Careful with chromosomes Careless with chromosomes Cancer cells are careless with their chromosomes Normal cell 46 chromosomes Cancer cell 80 chromosomes The cell division cycle Segregating your chromosomes wrong Chromosome loss causes retinoblastoma Segregating your chromosomes right NEEDED :Chromosome segregator and cell divider Chromosome attacher Sister chromosomes face back-to-back Checking mechanism (the spindle checkpoint) Sisters bound to oppose The spindle: locomotive tracks for chromosomes Microtubules fish for chromosomes Everything ready to go A snip sets sister chromosomes free The spindle checkpoint controls the scissors Spindle Checkpoint Waiting fixes some defects….. Time …..but not others X Time Linking chromosomes in meiosis Reorienting errant chromosomes (B. Nicklas) Brewer’s yeast: A geneticist’s best friend Using jellyfish to see in the dark Marion Shonn The spindle checkpoint prevents errors in meiosis I Wild Type Checkpoint mutant 98 % 81 % 2% 19 % Does the checkpoint help align chromosomes? The checkpoint does two jobs Down Syndrome births rise sharply with age 1/33 Risk 1/40 1/50 1/67 1/100 1/200 0 25 30 35 40 Mother's Age Why? 45 50 Chromosome linkage is different in Down Syndrome Rarer in Down syndrome More common in Down syndrome BUT, all linkage has occurred by mother’s birth Down Syndrome Rate increases with maternal age No overall change in recombination Less recombination near centromere More recombination near telomere Chromosome Alignment by Trial, Error Correction, and Delay Meiosis I Homolog Alignment Chromosome Reorientation in Meiosis I Chromosome Reorientation in Meiosis I