Class Notes (839,076)
Canada (511,183)
Biology (Sci) (2,472)
BIOL 200 (478)
Richard Roy (213)
Lecture

8. SSRs and DNA Transposons.pdf

4 Pages
88 Views

Department
Biology (Sci)
Course Code
BIOL 200
Professor
Richard Roy

This preview shows page 1. Sign up to view the full 4 pages of the document.
Description
(a) Human B-globin gene cluster (chromosome 11) Exon O tAlu site Pseudogene TABLE 6-1 Major classes of Nuclear Eukaryotic DNA and Their Representation in the Human Genome COPY NUMBERIN HUMAN GENOME FRACTION 0F HUMAN GENOME 55" (1.8) Protein-coding genes Tandemly repeated genes 6.1 kbt U2 snRNA <0.001 43 kb Repetitious DNA 1-500 bp Simple sequence DNA Variable Interspersed repeats (mobile DNA elements) 2-3 kb DNA transposons 300,000 6-11 kb 440,000 LTR retrotransposons Non-LTR retrotransposons 100-400 bp 1,600,000 SINEs Variable Processed pseudogenes Unclassified spacer DNA Variable Complete transcription units including introns. Transcription units not including introns. Protein-coding regions (exons) total 1.1% ofthe genome. "Length of tandemly repeated sequence. Sequences between transcription units that are not repeated in the genome;n.a.- not applicable. soURCE: International Human Genome Sequencing Consortium,2001 Nature 409:860 and 2004, Nature 431:931. (a) Human B-globin gene cluster (chromosome 11) Exon O tAlu site Pseudogene TABLE 6-1 Major classes of Nuclear Eukaryotic DNA and Their Representation in the Human Genome COPY NUMBERIN HUMAN GENOME FRACTION 0F HUMAN GENOME 55" (1.8) Protein-coding genes Tandemly repeated genes 6.1 kbt U2 snRNA <0.001 43 kb Repetitious DNA 1-500 bp Simple sequence DNA Variable Interspersed repeats (mobile DNA elements) 2-3 kb DNA transposons 300,000 6-11 kb 440,000 LTR retrotransposons Non-LTR retrotransposons 100-400 bp 1,600,000 SINEs Variable Processed pseudogenes Unclassified spacer DNA Variable Complete transcription units including introns. Transcription units not including introns. Protein-coding regions (exons) total 1.1% ofthe genome. "Length of tandemly repeated sequence. Sequences between transcription units that are not repeated in the genome;n.a.- not applicable. soURCE: International Human Genome Sequencing Consortium,2001 Nature 409:860 and 2004, Nature 431:931.Naveen Sooknanan McGill Fall 2011 SSRs and DNA Transposons: Protein coding genes can be solitary, or singly copy, genes or duplicate or multiple gene copies belonging to one gene family.  25-50% of genes are solitary. They are found unique gene species which are only once in the genome  The rest occur as multiple copies within the genome which form related sets called gene families o These gene copies can differ slightly because of evolution Gene duplication is an important process in evolution. New gene copies can either evolve a new function (functional exons) of degenerate over time (pseudogenes):  These changes, either good or bad, are caused by mutation to the genome  Pseudogenes were once coding regions of the gene but have lost their function, and therefore are treated like introns during transcription  A gene family contains gene clusters which originate from one gene o A gene family does not, however, have to be formed in clusters The following table shows the major classes of eukaryotic DNA in the human genome. We still don’t have an accurate reading of the human genome due the difficulty involved in the sequencing procedure: Protein coding genes make up more than half of the human genome. This proportion, however, includes noncoding portions of the gene such as introns found within the transcription unit.  When introns and untranslated ends at the 5’ and 3’ ends are removed, exons alone only form 1.1% of the human genome o Untranslated ends correspond to the 5’ UTR cap and the 3’ poly (A) tail located on the unprocessed mRNA molecule 1Naveen Sooknanan McGill Fall 2011 Tandemly repeated genes such as U2 snRNA, rRNA and tRNA have very high copy numbers are their genes are repeated one right after the other.  The mRNA coded by these genes are finished after transcription (i.e. don’t undergo translation)  Because of their very small size, these genes account for a very small amount of the entire human genome There are various kinds of repetitious DNA, all of which are relatively small in size and have very large copy numbers which is why they do not account for a lot of the human genome.  The introns of the protein coding regions of DNA are so large because they are littered with various forms repetitious DNA  Coding regions can also have repeating sequences in them caused by mutations Simple sequence repeats are divided into two subcategories: minisatellite DNA and microsatellite DNA:  Minisatellite DNA sequences are, in total, around 1-5 kbp in length. they are generally found in the telomeres (ends) and centromeres (a region located between the ends) of the gene o The repeat units are around 14-100 bp in length and are repeated 20-50 times (tandem repeat units)  Microsatellite DNA sequences are shorter than minisatellite sequences, around 1-4 bp in length (AAA, TTT, CAA, etc.). They are found in the transcription unit (usually in introns, but also in exons) o The arrays (total sequence) can be 600 bp in length composed of hundreds of tandem repeat units o Their function is not well known o Their expansion can cause neuromuscular diseases such as myotonic dystrophy and spinocerebrellar ataxia  Backward slippage during replication can cause a loop structure in the DNA as seen above o When this looped DNA strand is used as a template for replication, it will cause the synthesis of a daughter DNA strand which is one tandem repeat longer in length. o This leads to gradual expansion of the microsatellite sequence, whose consequ
More Less
Unlock Document

Only page 1 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit