Classical Laboratory Report : Corn Kernels, By Barbara Mcclintock
952 Words4 Pages
Classical Laboratory Report
In the 1940’s, Barbara McClintock was studying colored kernels, which were also known as maize. She numbered the ten chromosomes of maize from one to ten, one being a largest and ten being the smallest. While inspecting the breakage of these chromosomes, she noticed that one specific site of chromosome nine would break very frequently. She attributed this to two the presence of two genetic factors. The first she named the dissociation factor (Ds) and it was located at the breakage site. The second she named the activator (Ac), which activates the breakage of the chromosome. An illustration of this chromosome and the DS locus can be seen in Figure 1 (Anthony J.F. Griffiths, 2015). Figure…show more content… As seen in Figure 2, in the C gene, Ds cannot achieve mobility when it is not assisted by another element. When Ac element is present, however, Ds is able to move within the genome (transpose). This renders the Ds element non-autonomous. On the other hand, Ac element is able to move within the genome (transpose) without the assistance of another element. This renders it an autonomous element.
Both prokaryotic and eukaryotic organisms contain transposable elements (TE’s). There are two types of TE’s in prokaryotes, the insertion-sequence (IS) elements and the transposons. IS elements contain the genetic information required for their movement alone. However, transposons contain the genes required for their movement, along with additional genes (Anthony J.F. Griffiths, 2015). Eukaryotic transposable genes are also separated in two major categories, class 1 retrotransposons and class 2 DNA transposons. These two classes have distinct features that differ from one another. For class 1 retrotransposons to be copied, they must first be transcribed to RNA, from DNA, and then the resulting RNA must be reverse transcribed into DNA. The resulting piece of DNA can then be placed into the genome of the present chromosome (Anthony J.F. Griffiths, 2015). For class 2 DNA transposons, the transposons are catalyzed by enzymes, which are named transposase enzymes. These enzymes cut the DNA of a chromosome in specific or