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BIOB11 Lecture 1

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University of Toronto Scarborough
Biological Sciences
Aarti Ashok

BIOB11 Lecture 1 & 2 + Tutorial June 21/2012 – Gregory Mendel: munk who obsessed with pea plants, and listed various traits that he followed, then assigned traits – how many plants of a given characteristic were produced and then passed on from parent plant to individual --> gene – Alleles/genes can randomly unite at fertilization--> Mendel’s law of segregation – a dominant allele over the recessive allele – dominant allele masses the effect, ex:Aa = tall – segregation of alleles: segregation of dominant and recessive alleles – homozygous alleles contribute only that type of allele to the offspring, heterozygous alleles can contribute both – identity of parents in terms of alleles determines what percentage of offspring will have what kind of alleles – Law of independent assortment: each allele has its own effect on the offspring, ex: blue/brown eyes is independent of tall/short alleles – Physical basis of the units of inheritance: – Theodor Boveri: took one egg taken from organism and forced it with two sperms – three sets of alleles – initial stages of divisions were fine, but through differentiation stages, the blastists started to disintegrate over time – concluded that messing with the number of chromosomes will lead to inviable offspring – bivalent configuration: each pair of chromosomes associated with each other – chromosomes are genes/alleles that reside on the chromosomes. If the genes are on the same chromosomes, should they be inherited together? -- answer: not always. – Reason: there is breakage and exchange of info between homologous chromosomes, depends on how far apart the chromosomes are from each other – unable to be inherited together – why do breaks occur? -- there is intermingling, physical breaks and resealing and exchange of material between chromosomes – crossing over/chiasmata – Meiosis: – two separate separation events – 1. doubling of DNAand homologous chromosomes pair – 2. formation of chiasmata that allows exchange of DNA – Parental gamete: no crossing over/recombination – crossover gamete: formation of different gamete which has exchange of material between chromosomes – break between chromosomes = crossing over – the further apart two genes are, the bigger the chance that there will be a break between the two genes, wont be inherited together (unlinked traits) – Mendel's traits – S Bacteria killed mice, got pneumonia – fractionation of cell extracts: mix components of cells (proteins, lipids, DNA, etc) with R strains, DNAfraction when given to R strain caused virulent infection in mice – Do viruses inject DNAor protein? – Radioisotopes for labelling – S35 and P32 to label DNAand protein in two separate batches, then allow the virus to conquer – concluded that bac
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