How is the genetic code similar and different in all species?

Question

How is the genetic code similar and different in all species?

Answer 1

Genetics studies how living organisms inherit many of the features of their ancestors – for example, children usually look and act like other people in their family. Genetics tries to identify which features are inherited, and work out the details of how these features are passed from generation to generation.

Despite the variations that exist, the genetic codes used by all known forms of life on Earth are very similar. Since there are many possible genetic codes that are thought to have similar utility to the one used by Earth life, the theory of evolution suggests that the genetic code was established very early in the history of life, with phylogenetic analysis of transfer RNA suggests that tRNA molecules evolved before the present set of aminoacyl-tRNA synthetases.[9]

The genetic code is not a random assignment of codons to amino acids.[10] For example, amino acids that share the same biosynthetic pathway tend to have the same first base in their codons,[11] and amino acids with similar physical properties tend to have similar codons.[12][13]

There are three themes running through the many theories that seek to explain the evolution of the genetic code (and hence the origin of these patterns).[14] One is illustrated by recent aptamer experiments which show that some amino acids have a selective chemical affinity for the base triplets that code for them.[15] This suggests that the current, complex translation mechanism involving tRNA and associated enzymes may be a later development, and that originally, protein sequences were directly templated on base sequences. Another is that the standard genetic code that we see today grew from a simpler, earlier code through a process of "biosynthetic expansion". Here the idea is that primordial life 'discovered' new amino acids (e.g. as by-products of metabolism) and later back-incorporated some of these into the machinery of genetic coding. Although much circumstantial evidence has been found to suggest that fewer different amino acids were used in the past than today,[16] precise and detailed hypotheses about exactly which amino acids entered the code in exactly what order has proved far more controversial.[17][18] A third theory is that natural selection has led to codon assignments of the genetic code that minimize the effects of mutations.[19].

http://en.wikipedia.org/wiki/Genetic_cod...

The sequence of nucleotides in DNA or RNA that determines the specific amino acid sequence in the synthesis of proteins. It is the biochemical basis of heredity and nearly universal in all organisms.

The rules of the genetic code are virtually the same for all organisms, but there are some interesting exceptions. In the microorganism Mycoplasma capricolum, UGA is not a stop codon; instead it codes for tryptophan. This alteration in the code is also found in the mitochondria of some organisms. In addition to changes in the meanings of codons, a modified system for reading codons that requires fewer tRNAs is found in mitochondria. See also Gene; Gene action; Genetics.

http://www.answers.com/topic/genetic-cod...

The first detailed look at the human genome has revealed a few surprises.

From a genetic perspective, all humans are Africans, either residing in Africa or in recent exile

Svante Paabo, Anthropologist  

Not only do we have fewer genes than predicted but we are also astonishingly alike. Every person on Earth shares 99.99% of the same genetic code with all other people.

The biological difference between individuals amounts to a fraction of the three billion letters in the human genetic code. "You and I differ by 2.1 million genetic letters from each other," said Dr Craig Venter, who led the private bid to crack the human code. "Probably only a few thousand of those differences account for the biological differences between us, which means we all are essentially identical twins - even more than I thought."

Our genetic similarity to other creatures is firm proof of Charles Darwin's theories on the unity of life.

Worms and flies

"We can now start seriously investigating how it is that humans, who we think are so complex, can manage with only a relatively modest number more genes than worms and flies," said Martin Bobrow, a professor of medical genetics at Cambridge University, UK.

"We are confirming Darwin, it's great to be getting the molecular correlates of what Darwin hypothesised 150 years ago," said Sir John Sulston, who spearheaded the UK side of the Human Genome Project.

http://newsvote.bbc.co.uk/2/hi/science/n...

Answer 2

In addition, the genes of human and chimpanzees are between 98-99% the same.  In fact, there is only 10% difference between the genes of humans and bacteria.  

You might find the books of Matt Ridley of intererest.

Answer 3

In all true cells, DNA contains the genetic code that controls the metabolism of the organism.  The sequence of nucleotides of adenine, thymine, cytosine, and guanine determines the code.  In a given gene, the sequence of these four compounds determines the structure of polypeptides or proteins.  The proteins may be structural or have some metabolic function such as enzymes, antiboides, clotting proteins, etc.

Species (and even individuals within the species) have similar but slightly different genetic codes.  Chimps are humans have very similar genes!  But enough difference that humans would not be good chimps and chimps aren't good humans!