Model Organisms & Tools of Cell Biology. Lecture 3 Autumn 2007. Learning the Unknown. You are a car mechanic Would you rather know a little bit about the working of every car every constructed… … or everything about a representative one from each category? Science is no different!.
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This is now the main model plant system for genetics.
Its small genome, and the recent application of classical genetics has put it far ahead of other models of agricultural importance (tomato, tobacco, corn etc.)
It's genome has been fully sequenced.01_33_model plant.jpg
Drosophila sp. ‘Fruit Fly’
Usually the species Drosophila melanogaster -
Easily raised in lab, rapid generations, mutations easily induced, many observable mutations.
Many clues to development and genetics
Saccharomyces cerevisiae, baker's yeast or budding yeast (used in brewing and baking)01_32_model eucaryote.jpg
Early studies on this enabled us to get a great grasp on the cell cycle
100X - cells
1000X - organelles
10,000X - organelles
100,000X - proteins
1,000,000X - atoms
The organism grows at one temperature (permissive) but fails to do so at a different one (restrictive).01_35_Yeast mutation.jpg
All the yeast colonies grow at one temperature (23C), but if one places the same cells at 35C some of the colonies fail to grow - what is wrong with the ones that fail to grow?
Sequence analysis has taught us that there are about 200-300 genes required for the most basic cell survival.
Comparisons across species shows that many genes are common from simple bacteria to complex life forms, and that life uses similar processes01_37_amino acid sequ.jpg
290,000,000,000 (100 times the size of a human genome)
Bufo bufo (cane toad)
Homo sapiens (Man)
3,000,000,000 (3 billion base pairs - 24 chromosomes - [22, X, Y])
Muntiacus muntjak vaginalis (Indian deer)
Boa constrictor (snake)
Rhinolophus ferrumequinum (bat)
Plasmodium falciparum (malaria parasite)
Human immunodeficiency virus type 1 (HIV)
Among the organisms whose genomes are sequenced, genome size does not correlate with the number of genes.
Species Size of genome Number of genes
3.0 billion base pairs 25,000 ?
Fruit fly (Drosophila melanogaster)
120 million base pairs 13,601
Baker's yeast (Saccharomyces cerevisiae)
12 million base pairs 6, 275
Worm (Caenorhabditis elegans)
97 million base pairs 19,000
4.6 million base pairs 4,403
Arabidopsis (Arabidopsis thaliana)
125 million base pairs 25,000