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Lecture 5

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Western University
Biology 1001A
Tom Haffie

Biology 1001 Lec 5: Genome Structure & Variation September 24, 2012  A genome is all of the DNA sequence in one copy of an organism’s chromosomes  A given plant cell has 3 different genomes  It has a nuclear genome and a mitochondrial genome  Plants also have chloroplasts with a genome inside  Most of the time, a genome refers to the nuclear genome  The size of a genome is known as “C”  The “C” of a genome refers to how much DNA you have in one copy of your genome  Sometimes, C is expressed as a weight (pictograms) , or sometimes it’s expressed in base-terms (Mb = megabase = 1 million bases)  Bacteria & Archaea have relatively small genome sizes, though the range of genome size among different species is pretty large  You get the impression that humans have more DNA because they are more complex; however, there is very little correlation between complexity and genome size  i.e. several different types of salamanders and flatworms have much larger genomes than humans  “C” is not for “complexity”  “C” varies widely between one taxonomic group  One C-value is distributed over one set of chromosomes  C value refers to only one copy; i.e. if it is diploid, only look at one of the pair  Linear chromosomes are almost only found in Eukarya  Almost all of the prokaryote cells have circular chromosomes  Mitochondria and chloroplasts have circular genomes  Eukaryotes in their nuclei have linear genomes  The number of chromosomes you have has nothing to do with complexity; entirely irrelevant  “P
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