Berkeley MCELLBI 140 - Lecture Notes (8 pages)

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Lecture Notes



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Lecture Notes

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Lecture Notes


Pages:
8
School:
University of California, Berkeley
Course:
Mcellbi 140 - General Genetics
General Genetics Documents

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Walter Sutton 1902 03 What was clear about meiosis 1 That it involves two consecutive cell divisions not one 2 That the number of chromosomes appears to be reduced as a result of that fact MCB140 9 5 08 1 MCB140 9 5 08 2 Sutton s conclusions 1 Chromosomes have individuality 2 Chromosomes occur in pairs with members of each pair contributed by each parent 3 The paired chromosomes separate from each other during meiosis and the distribution of the paternal and maternal chromosomes in each homologous pair is independent of each other MCB140 9 5 08 3 The most important fact in classical genetics MCB140 9 5 08 4 On chromosomes chromatids sisters nonsisters and homologs both Mendel s first and second law are explained by the behavior of chromosomes during meiosis MCB140 9 5 08 5 MCB140 9 5 08 6 1 Fact 1 Furthermore The human genome contains 35 000 genes Each gene is from a physical perspective a stretch of DNA The sequence of base pairs in that DNA encodes the amino acid sequence of a protein note this simplified narrative disregards noncoding DNA elements of a gene such as regulatory DNA stretches untranslated 5 and 3 UTRs introns and polyadenylation signals furthermore most of the RNA produced by the human genome is noncoding but you will learn that in graduate school if you go there In principle it is imaginable that each gene could be on a separate piece of DNA so the nucleus of a human cell would contain 35 000 separate pieces of DNA In actual fact in a human being the genome is distributed onto 23 pieces of DNA well 23 pieces plus one additional somewhat important gene on a separate small piece of DNA but more on that later What you call those pieces depends on who you are MCB140 9 5 08 7 1 genome 35 000 genes 23 pieces of DNA MCB140 9 5 08 8 Genetic unity of a species For now let us call EACH of those pieces a chromosome More later on that for now bit We can now ask those 35 000 genes mentioned earlier how are they distributed between those 23 chromosomes In



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