Genomes are packages of information transferred from parents to offspring. Join this presentation to learn about some basic features of this information by selecting the following chapters
Due to the use of low resolution images in this internet version, some details are hard to recognize. Ask for a free PowerPoint presentation to see more (firstname.lastname@example.org).
This page displays the genomes of the bacterium Mycoplasma genitalium, the archaeon Methanococcus janaschii, the yeast Saccharomyces cerevisiae, the model plant Arabidopsis thaliana, the fruit fly Drosophila melanogaster, man and the amphibium Necturus lewisii (in the background). Continue this presentation to learn more about the planets displayed.
Genes and genomes
Genomes correspond to strings of DNA (yellow) – with genes like pearls (red).
While we have at least some idea about the meaning of the gene portion of the string, the DNA-sections between those genes still are pretty mysterious.
Wrapping the DNA around a sphere
For a better presentation let‘s wrap that string around a sphere
Well, here we‘ve wrapped two parallel strings around a sphere, but that doesn‘t matter for the moment…
A genomic planet
Now we translate the gene density (red dots) into continents and mountains and our planet is ready.
Large distances between two adjacent genes lead to the formation of oceans; that‘s what‘s happening in the equatorial belt of our planet.
Most genomes are composed of more than one string of DNA.
The sequences shown so far correspond to the small plant Arabidopsis thaliana. Each nucleus of this plant contains five pairs of different strings of DNA. These strings are called chromosomes and in the case of Arabidopsis we have only been looking at one pair of those chromosomes. (Chromosome I; to indicate that there are two copies of this chromosome, our sphere was constructed from 2 parallel strings.)
Here are the five different chromosomes from Arabidopsis thaliana shown in the same technique as before.
A plant genome
Which summarizes to: Our first real planet – the genome of the model plant Arabidopsis thaliana.
There are still some details, we will add in the following slides…
Each chromosome has a central region used for moving and sorting – the centromer marked by red cones here.
Only centromers from chromosome I, III and IV are visible; the other centromers are located on the backside of the planet. Because each chromosome is present in two copies, there are two centromers in each case.
Most cells contain DNA outside their nucleus. In the case of Arabidopsis thaliana there are small DNA-molecules within the mitochondria and the plastids.
The genes of the mitochondrial DNA-molecule are arranged around the north pole…
…the genes of the plastid DNA-molecule are arranged around the south pole.
Let‘s have a look at the genomes of some other organisms…
Arabidopsis thaliana is already a pretty complicated organism. Let‘s start our tour across the living world with something more simple: bacteria.
This is the genome of pest bacteria (Yersinia pestis). Genes clearly responsible for the deathly properties of these organisms are marked by volcanoes.
In the tree of life, bacteria have a sister group, the archaeae. Although both groups look pretty much alike, there are a many clear differences.
Archaeae are adapted to living in extreme environments. The organism corresponding to the genome displayed here (Methanopyrus kandleri) thrives at the bottom of the seas at temperatures above the boiling point.
Genes characteristic for the group archaeae are marked by yellow labels, genes important for living at high temperatures by volcanoes and genes important for the ability to generate methane by little red flames.
Bacteria and archaeae are clearly separated from each other. Nevertheless, they exchange genetic information. To demonstrate the extent of this unusual process, here comes the genome of a bacterium (Escherichia coli), where all genes not obtained by usual inheritance (i.e., from his ancestors) have been marked by craters.
Bacteria and archaeae are the two basic groups of life. They have many things in common: both groups are very old, both comprise rather simple (but efficient) organisms. The genomes are rather small and the genes are closely spaced in these genomes (so there are no oceans on the respective planets but many mountains).
All organisms we can see with the naked eye (and many others as well) are members of a third group. Here, for a start, the genome of a rather simple, microscopic species is displayed.
Members of this third group are more complex: They have complex cells and they often consist of many different cells. In addition, they have large genomes, which are composed of chromosomes. Individual genes often are widely spaced. (This means larger planets with oceans and plains.)
Origin of eukaryotes
A large number of scientific results suggests that this third group has originated from the fusion of members of the two other groups, bacteria and archaeae.
Gene archaeology can still detect remnants from this ancient fusion event.
One reason (amongst many others) for the large size of genomes from the third group is the presence of autonomous elements within the genome. These elements can multiply and insert at various places into the genome.
Here is a genome of a model insect (Drosophila melanogaster), where all such elements have been marked by black labels.
The information stored in genomes is regulated in a very complicated manner.
This presentation of the human genome shows two genes (important in inflammation processes and tumor formation) involved in the regulation of other genes.
All the genomes displayed so far are available as historical maps. In case you are interested in exhibiting these maps, feel free to contact me (email@example.com).
The map presented here shows the genome of the pest bacterium Yersinia pestis.