Experimental Systems

• Relatively simple structure Fig. 1, ease and speed of growth [divides every 20-60 min], clonal populations can be easily isolated on soft agar, excellent models for studyting fundamental aspects of cellular biochemistry and molecular biology.
• Genome 4 million base pairs - encodes about 4000 different proteins
• In contrast - the human genome is about 1,000 times more complex and encodes ~ 100,000 different proteins HUMAN GENOME PROJECT

Yeasts

• E. coli not useful for studying aspects of cell structure/function or molecular processes which are unique to eukaryotes.
• Yeasts Fig. 2- the simplest eukaryotes
• easy to grow, fairly rapid reproduction [once every 2 hours] etc.
• Most studied species - Saccharomyces cerevisiae
• Genome contains ~14 million base pairs [roughly 3 x that of E. coli] 16 linear chromosomes
• Exhibits the typical features of a eukaryotic cell although much more simple than most eukaryotes.
• Easily grown as a colony on agar - different nutrient requirements
• General principles seem to apply tø all eukaryotic cells.

Dictyostelium discoideum

• cellular slime mold Fig. 3
• 10X the genome of E. coli
• easily grown, amenable to genetic manipulation
• If plentiful food - it grows as a single-celled amoeba, feeding on bacteria and yeasts
• Highly mobile - good model for animal cell movement
• Aggregation if adequate food supply not available - forms wormlike structures called slugs composed of ~ 10,000 individual cells
• Model for cell signaling and cell/cell interactions

Caenorhabditis elegans . [ aka C. elegans ]

• nematode (round worm) Fig. 4
• one of the most widely used models for studies of animal development and cell differentiation
• genome 100million base pairs
• adult worms are composed of 959 somatic cells + 1000 to 2000 germ cells
• Easily grown
• embryonic origin and lineage of ALL the cells has been traced

Drosophila melanogaster

• fruit fly Fig. 5
• crucial model organism in developmental biology and genetics
• Genome similar in size to C. elegans
• 2 week reproductive cycle
• many many genes analyzed in detail
• has led to striking advances in understanding the molecular mechanisms that govern animal development.
• ESPEC. formation of body plan of compelx multicellular organisms.

Arabidopsis thaliana

• Plant Fig. 6 - contributed greatly to our understanding of plant development and plant molecular biology
• genome 70 million base pairs
• ~ 5X that of yeast and similar to Drosophila and C. elegans
• easy to grow
• easy to derive mutants, etc.

African clawed frog - Xenopus laevis Fig. 7

• large eggs, large #s of eggs - develop outside the mother
• complete cycle in lab

Laboratory mouse

• inbred strains which are genetically identical

• Fig. 8 specific genes have been introduced into the mouse germ line, so that their effects on development or cell function can be studied

• specific genes have been deleted in the mouse germ line