Genome

Genome

Ch. 1-

Ridley begins his book with a dramatically ambiguous chapter one. He focuses on a biblical concept of "the word" in the very beginning of the earth. The word Ridley refers to is genomic information stored in RNA molecules. Long has debate continued about which came first, the DNA that codes for protein or the proteins that catalyze chemical reactions. Ridley suggests that RNA came first, with its ability to copy itself without assistance. The first chromosome contains a gene that is suspected as being the first gene, able to duplicate itself for it is repeated on the first chromosome over and over again.

Terms: 'ur-gene': probably the very first gene, able o duplicate itself and therefore catalyze reactions using chemicals around it. May have been made of RNA.

'ribo-organism': before any other organism, Ridley suggests that RNA began to evolve into larger organisms that paved the way for life.

'LUCA': Last Universal Common Ancestor, or first sophisticated organisms that stored its genetic code on DNA, a more stable convention, made its enzymes of proteins and used RNA to intermediate the two.

Questions: Is it in the nature of RNA to utilize reverse transcriptase and form DNA, or did this happen by mutation or other modes of evolution?

What about the chemical make-up of RNA empowers it to replicate itself?

How does bacteria acquire genes by ingesting other bacteria?

CH 2-

Ridley uses chromosome 2 to illustrate the subtle distinction between species, especially man and chimpanzee. Both Chimpanzees and gorillas have 24 pairs chromosome. Humans have only 23 because our second chromosome is the product of a fusion between two medium-sized ape chromosomes. That is why it is the second largest in our collection. Notwithstanding our ecological success, and the many apparent discrepancies between humans and chimps, we are ninety-eight percent chimp and they are ninety-eight percent human. Which means the two species share all but two percent of our genomes exactly.

Terms: 'aquatic hypothesis': suggested origin of the missing link between species. Separation often drives speciation, so theorists suggest that a gigantic marine cataract isolated a small population of missing links on some island.

'East Side Story': similar theory that suggests that it was a mountain range or a river five million years ago that caused the split and catalyzed speciation.

Questions: Is there any evidence for these supposed splits or isolation of small populations that drove speciation? How would we ever come to these conclusions?

If Chimpanzee is more like man than ape, where does the Rhesus monkey fall into the evolutionary process from ape to man?

What mutation caused for the lack of elongation of the jaw apparent in the human skull?

CH 3-

Ridley uses the discovery of a gene on chromosome 3 involved in the disease Alkaptonuria to relate some of the history leading to the discovery of genes themselves. In 1902, Archibald Garrod attempted to treat patients suffering with the disease and was assisted by the studies of Brother Gregor Mendel. Mendel's findings rivaled the popular notion of 'blending inheritance', which Darwin actually based his theory upon. However, this theory began to dissipate as more light was shed upon the subject of inheritance. Driven by this research, Watson and Crick began to postulate that genes were made of DNA, not proteins.

Terms: 'blending inheritance': the idea that inheritance consisted of the simple blending of parental fluids. Changes would be diluted, therefore idea was dropped.

'Alkaptonuria': genetic disorder that produces symptoms such as arthritis and the blackening of ear wax and urine. Garrod found the disease to be recessive.

'homogentisate dioxygenase': protein that is defected by above disease. One single point mutation is responsible for the disabling of the protein.

Questions: Did Mendel get 'lucky' by choosing traits found on different chromosomes therefore not dealing with linkage problems or did he throw out data that didn't support his theory?

What led Crick to assume that tRNA must exist?

How would the process of DNA translation and transcription differ if a 'comma free' code were actually used in nature?

CH 4-

Chromosome 4 contains the gene that encodes the huntingtin protein. Nancy Wexler found it in 1993 on the top of the chromosome. The repetition of the codon 'CAG' in the middle of the gene results in a long stretch of glutamines in the middle of the huntingtin protein, which is now known to be the cause of Huntington's disease. Hunitington's was the first completely dominant disorder we have found and its symptoms are terrible. The severity of the depression, hallucinations and delusions, as well as the age of onset is determined by the number of repetitions found in the gene. Not a single case of the disease has been cured, and therefore this gene truly decides the life of us all.

Terms: 'polyglutamine diseases': more than a dozen diseases are caused by expanded three-letter repeats.

'Wolf-Hirschhorn syndrome': disease diagnosed by the absence of the wolf-hirschhorn gene found normally on chromosome 4. (victims die young.)

Questions: Since 1993, how has the research for Huntington's disease therapy changed, are we getting any closer to a cure?

Ridley suggests that codon repeats happen because it is easy to add another codon when there are already so many being added. Wouldn't be just as easy to omit the addition of such codon?

What is the phenotypic result of a lack of CAG repeats on the gene?

CH 5-

Our phenotypes are the result of genotype and environment. Not only does a combination of these two affect our phenotype, but also environment can physically alter our genetic make-up. There are multiple candidates for the 'asthma gene', but most scientists point to eight on chromosome 5 as culprits. Theories have arisen involving our immune systems and the expectance our bodies have to be polluted and derive antibodies against such pollutions. Urban areas that are relatively sanitized,