Monday, March 8, 2010
Gene Alteration
Evolution has a lot to do with gene alteration among different individuals in a species and how those traits get passed on to their offspring over thousands of generations and how eventually this leads to the evolution of a completely different species that cannot interbreed with the previous. From our molecular genetics and DNA & protein synthesis units, how do genes alter? What are the different ways that they can be altered? How do these alterations affect what proteins are made and what genes are turned on and off? Explain the differences between changes in the genome and epigenome. Explain how all these genetic alterations lead to the process of evolution.
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Genes can be altered through mutation of alleles. The production of polypeptides from genes in the genetic code is contingent upon the molecular processes of transcription and translation. In Eukaryotes, the process of transcription begins with an enzyme called RNA polymerase which binds to a “promoter region” and “pries the two strands of DNA apart and joins the RNA nucleotides as they base-pair along the DNA template”. Point mutations may affect the transcription of genetic code and may be transferred to offspring if it occurs in a gamete. A “base-pair substitution” may replace one pair of nucleotides with another pair of nucleotides. Such a substitution may code for the same amino acid, and subsequently not affect the production of the given protein. When the pair codes for another amino acid, the mutation is called a missense mutation and the effect on protein synthesis tends to vary. The most grave of all mutations is an insertion or deletion of a nucleotide, especially in odd numbers which may adversely affect the function of a gene. Many mutations are known to cause diseases; An example of a disease that is linked to genetic mutation is cystic fibrosis (Encyclopedia Brittanica)
ReplyDeleteWhen populations are isolated or proliferate in environments different from that of others of the same species, the process of natural selection will continually select for those mutations that lead to favourable adaptation in the context of survival and reproduction. Jerry Coyne notes that the “geographic isolation” of two populations may give rise to radical speciation as a result of “..longer tail feathers in one population and orange color in another” which affects “sexual selection”. (Coyne, 176). Thus, Coyne emphasizes that speciation is the result of random ‘gene alteration’ and the effects of natural selection on the amplification of such traits in a population.
The role of the environment and geographic location is especially important since environmental mutagens may often cause detrimental mutations in the genetic code. These mutagens include UV light, x-rays and carcinogens.
Such point mutations that occur before transcription of the genetic code are not solely responsible for the divergence of a population into a new species. Through the addition of acetyl groups to histones, the proteins at the core of a DNA strand, and the addition of methyl groups to certain base pairs, the expression of certain genes may be regulated. The genes expressed at a given time in development depends on such regulatory processes. These patterns may be inherited by offspring and is called genomic imprinting. Such epigenetic inheritance passes on patterns of gene expression that are reversible but may change the phenotypic expression of a gene in offspring. Since natural selection only selects for genes and traits that are expressed, epigenetics and the regulation of gene expression may play a role in speciation.
Campbell, Neil A. Reece, Jane B.. Biology, AP Edition 8e. 2008. San Francisco, CA.
mutation. (2010). In Encyclopædia Britannica. Retrieved March 20, 2010, from Encyclopædia Britannica Online School Edition: http://www.school.eb.com/eb/article-9054492
Why Evolution is true. Jerry Coyne