Amanda's Exploration into Genomes and Diversity

Sidestepping Mutational Meltdown
Eric A. Shoubridge and Timothy Wai

Shoubridge and Wai present the fascinating results of an experiment in which mouse mitochondrial DNA with severe mutations is not passed down to later generations. The mitochondrial genome codes for important protein components of the organelle’s respiratory equipment as well as transfer and ribosomal RNAs. The first generation germ cell with severe mutations in the mitochondrial DNA is either destroyed by autophagy, in which the cell decomposes its own components, or through selection during the replication process. Therefore, the mature cell no longer has the mitochondrial mutation. The mystery as to why this occurs is still unsolved. This could be useful for explaining how mutations occur in genes and DNA. It would also be interesting to investigate specific instances when mutations are no longer transferred in later generations and the possible reasons why this occurs so that a deeper understanding of how genes work is reached.

To read the entire article, go to:
http://www.sciencemag.org/cgi/content/full/319/5865/914?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=genome&searchid=1&FIRSTINDEX=0&issue=5865&resourcetype=HWCIT

Legs, Eyes, or Wings--Selectors and Signals Make the Difference
Markus Affolter and Richard Mann

This article is very useful in order to see how genes work in that it shows the experimental results of studies done on the fruit fly Drosophila melanogaster. This article discusses the variations of body plans of specific organisms as seen through specific genes. The scientists that led this experiment focused on selector genes that encode transcription factors that control the development of sets of cells that give rise to specific structures in the adult organisms. To build specific structures such as a leg or wing in the fruit fly, the cells also need to know where these structures should be located in the adult organism. This is accomplished through small sets of intercellular signaling pathways. In order to activate the transcription factors, a signaling effector is necessary to tell the cell which signaling pathway to use so that the specific structures can be produced. The interaction between the selector and signaling protein complexes are vital so that specific responses can be made to create structures such as wings, antenna, legs, and eyes in the Drosophila melanogaster. This article is important in showing the various intercellular processes that are necessary for genes to undergo so that organisms can have the right structures needed to become an adult.

To read the entire article, go to: http://www.sciencemag.org/cgi/content/full/292/5519/1080

While working with DNA sequencing, you study a tube containing plasmid DNA. You are studying the plasmid so that you can draw a map of the plasmid showing the relative positions of recognition sites for the restriction enzymes XhoI and SalI. You perform three separate reactions, mixing your plasmid DNA with: 1) XhoI alone, 2) SalI alone, and 3) XhoI and SalI together. You separate the products of these reactions by gel electrophoresis, with each of the three reactions in a separate lane on the gel. The gel tells you that the reaction with SalI produced a single DNA fragment of length 5000 bases; the reaction with Xhol produced two DNA fragments of length 2000 bases and 3000 bases; and the reaction with both XhoI and Sall produced three fragments of length 500 bases, 2000 bases and 2500 bases.

Draw a map of the plasmid showing the relative positions of the Xhol and SalI sites, and the distance in the bases between these sites.

Here is the answer for the previously posted example exam question:

First you draw a circle in which there is one site for Xhol(1). Then the next site is for Xhol(2) with 2000 bases in between the two sites. Finally there is a site for Sall 500 bases away from the second Xhol(2) site. Therefore, that leaves 2500 bases between the Sall site and the first Xhol(1) site.

Sorry I couldn't draw the actual circle for you. Good luck studying for the exam!