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Lecture 5

Biology 1001A Lecture 5.pdf

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Western University
Biology 1001A
Beth Mac Dougall- Shackleton

Biology 1001A | 2012 LECTURE NOTES Lecture 5: Genome Structure & Variation –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– - In a study of the worldwide acceptance of evolution, people were asked to what degree they accepted the truth of the following statement: “Human beings, as we know them, developed from earlier species of animals.” Answer: the statement is probably true Genome - a genome is all of DNA sequence in one copy of an organism’s chromosomes - plant cells have both nuclear, mitochondrial, chloroplast chromosomes - most of the time, we are referring to nuclear genomes - the Amount of DNA is one genome is called “C” - sometimes C is expressed as a mass or sometimes it is expressed as the number of base pairs (mega bases, 1 million) - genome size is quite variable within a taxonomic group - in general, genome size increases among eukaryotes - there is very little correlation between complexity and genome size - some species of crustaceans, flatworms, salamanders etc, have more DNA than humans - there is a huge difference between some organism of the same species, an example is -2 3 the protozoans, which range from 10 to mega bases to 10 mega bases - how do we explain the wide variation in genome size? - one C-value is distributed over one set of chromosomes - C-value enigma is the massive variance in the amount of DNA in a genome within the same taxonomic group How Many Chromosomes In... - a goldfish 94 - an oak tree 24 - Watson (dog) - linear chromosomes are (almost) only found in eukarya - almost all bacteria and archaea have circular chromosomes - mitochondria and chloroplasts have circular chromosomes - number of chromosomes has absolutely nothing to do with complexity and therefore has no taxonomic value Ploidy - refers to the number of sets of chromosomes - n refers to the number of sets of chromosomes that an organism has - humans are diploid and therefore have 2 - some organisms (such as lizards) have three sets and are therefore called triploid - the n = C Biology 1001A | 2012 The Chromosome - a chromosome is packaged chromatin: DNA plus protein - the DNA is wound around proteins called histones - the protein/DNA complexes are called nucleosomes - each “X” shaped chromosome is made of two DNA molecules - there is one molecule of DNA on each side of the chromosome, one for each chromatid What is your DNA sequence? - The Human Genome Project: Sequence of the (almost) entire genome - 2000 – working draft compiled from DNA of several anonymous donors - the first sequence was not the sequence of a particular individual - mid 2000’s – individual sequences of Craig Ventor and James Watson - about 2010 – individual sequences of Han Chinese, Korean, Yoruba, Bantu (Desmond Tutu) Neanderthal, unborn fetus, etc. - there are
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