On page 158-159 of the Methly Madness: Road to the Final
Phenotype, Dr. Moalem introduces the relatively new concept of epigenetics. The
word was coined in 1940 and gets its name from the Greek prefix of epi which
means in addition. This new layer of genetics involves a set of reactions that
act outside and above the genetic code, and change the results of the phenotype
without changing the code itself. In Duke university, scientists mated two fat
yellow agouti mice and received thin brown babies as
the offspring. This genetic mystery was solved with the process of DNA
methylation, which uses the methyl group to bind to a gene to change the way
the gene can express itself.
Explain the basic concepts of Epigentics( where the genes
are effected, how they are effected, what effects them, and when they may be effected)
and how genes can turn on and off. Explain the concept of operons and how they
can either induce or repress transcription or translation in genes. In this
case, what gene was turned off to result in the thin brown phenotype. Provide
outside examples of how genes can be turned off and then briefly explain their
effects on a specie, then explain the major effects of turning this gene of in
the mouse. Relate this experiment of mice to Big Idea three, how living beings
store information vital to life, and how the gene coding has not been effected
but still produces a different result.
Rahul Kosgi( rkosgi4@students.d125.org)
The literal meaning of epigenetics is "above genetics." Epigenetics examines how certain epigenetic tags, such as methyl groups and histones (carbon-hydrogen compounds called methyly groups turn off; histones extent), which float above the genome, can turn genes off or on to what extent. Epigenetics also deals with the heredity of certain changes in gene expression.(http://www.youtube.com/watch?v=kp1bZEUgqVI)
ReplyDeleteAs for the details of how epigenetic tags affect gene expression, two main tags are involved: carbon-hydrogen compounds called methyl groups and proteins around which DNA winds called histones. Methyl groups function as a switch, while histones function as knobs (for volume control). In histone acetylation, acetyl groups attach to histone tails, neutralizing the histone tails. Acetylated regions of histones help transcription proteins access certain genes more easily. Consequently, the histone tails do not bind to nucleosomes and chromatin has a looser structure, promoting stronger gene expression. Conversely, a tighter chromatin structure would weaken gene expression. In DNA methylation, methyl groups attach to genes to often turn genes off. Often, DNA methylation occurs during cell differentiation in the embryo and inactivates genes for generations by methylating the daughter strand of DNA after each round of replication. In general though, changes in gene expression not only during developmental periods, such as puberty, but also are affected by a person's daily actions and emtions. (Campbell 357-358)
Whenever DNA is transcribed, the operator of the operon must be open. There are two types of operons: repressible and inducible. In repressible operons, certain corepressors attach to and activate repressor proteins, which bind to operators and prevent transcription. In inducible operons, inducers inactivate repressor proteins, keeping the operator open for RNA polymerase to pass through. To connect this back with gene regulation, whenever methyl groups bind to genes either the corepressors activate repressors or inducers are not present. In the mice at Duke, the augoti gene, which was responsible for yellow coats and fatness, was turned off. This experiment relates with Big Idea 3, which states that living systems sotre, retrieve, transmit, and respond to information essential to life processes. Although humans did indeed manipulate the mice to turn the agouti gene off, the offspring maintained the off position of the agouti gene because being thin and brown was arguably important for health and survival.The experiment illustrated for the first time that a mother’s offspring can “permanently alter gene expression without altering the genes themselves” (Moalem 159) This could also relate with Big Idea 1, which says that the process of evolution drives the diversity and unity of life. If fat mice experience trouble in escaping from preying mice, then its subsequent offspring could have its agouti gene turned off to survive and reproduce.
Another example of genes being turne off is DNA methylation of genes that may promote cancer. Esteller, a an epigenetics researcher in Spain, found out that there was "a significatnly higher amount of methylation in the newborn than in centenarian", which proves that cancer is responsible for many deaths. (http://news.sciencemag.org/sciencenow/2012/06/aging-is-recorded-in-our-genes.html)
-Ken Saito (ksaito4@students.d125.org)