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Lecture 17

Lecture 17 - Searching for Answers in our Genome

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University of Toronto Mississauga
Esteban Parra

Searching for Answers in our Genome Molecular Anthropology - Molecular anthropology is a discipline of physical anthropology focused in the study of the genetic variation in human populations - Information on genetic polymorphisms, at the protein or DNA level, is fundamental in order to understand the origin, demographic histories and genetic relationships between contemporary human populations. A Wonderful Research Tool: the PCR Technique - The discovery of the Polymerase Chain Reaction (PCR) technique (Mullis, 1983) opened a wide range of possibilities for the study of the genetic variation directly at the DNA level. o PCR – polymerase chain reaction: technique to amplify the DNA multiple times o This technique revolutionized the way we study the DNA; so he got the nobel prize for this Types of DNA Markers - There are many types of DNA markers in the human genome that can provide information about our evolution. - A brief description of some of these markers follows. DNA Markers: Single Nucleotide Polymorphisms (SNPs) - SNPs are single nucleotide base substitutions. o They are just changes in one letter o This is frequent in our genome - SNPs are the most abundant markers in the human genome. More than 37 million SNPs have been reported in the most recent 1,000 genomes data release. DNA Markers: Alu Insertions - Alu retroelements are part of the family of jumping genes known as short interspersed elements or SINEs. Alu sequences are roughly 300 nucleotides in length, and they are dispersed along the human genome. o They are polymorphic; and are present in some chromosomes (can be used to study evolutionary events) - Some Alu sequences are polymorphic in human populations (presence/absence of the Alu insertion). The insertion of an Alu sequence only happens once in a particular genome location. o You can see whales and hippos share some of these insertions (they are closest relatives) Detection of Alu Polymorphisms - Electrophoresis: technique separating fragments by size (depending on what substrate they run) o A way to identify them, as DNA is negatively charged (and it will go towards the positive pole) DNA Markers: Microsatellite Polymorphsms (aka STRs) - Microsatellites are tandemly repeated short nucleotide sequences (2-13 nucleotides) dispersed all over the genome. In many cases, they show polymorphism in the number of tandem repeats. o They are located in many places in the genome (we can work with these for many human evolutionary studies) o Can be used in paternity testing and forensics Microsatellites - Microsatellites show a faster mutation rate than other markers (SNPs, Alu insertions). o This is because of the nature of repeats where they have different mechanisms - Microsatellites are very useful markers in human evolution, and also in forensics and paternity testing. Where to Look in the Human Genome - We can explore several regions of the human genome to look for answers about the evolutionary history of our species. Autosomal Markers - The 23 chromosomes of the human haploid set can be divided into 22 autosomes and a pair of sex chromosomes (X and Y). Y-Specific Markers - Two regions can be distinguished on the Y chromosome. - The pseudoautosomal region, where recombination occurs between X and Y chromosomes. o In the tip of the Y chromosome; and only region that recombines with the X- chromosome (during meiosis) - The Y-specific region, where there is no recombination and is only transmitted from the paternal line. This Y-specific region comprises more than 95% of the modern Y chromosome o In this part of the chromosome, there is a sex determinant region  key factor in the development of males More About the Y Chromosome - There are only a few genes in the Y-specific portion of the Y chromosome. The paper describing the results of the Human Genome Project indicated that there are 78 protein- coding genes, which encode 27 distinct proteins. o This is why there are X-linked traits, because these traits are not found as counterparts on the Y-chromosomes - There is evidence that there have been recent transposition of material from the X- chromosome to the Y-specific portion of the Y chromosome (around 3-4 my. ago) o When they compared regions in the Y-chromosome, it is very similar to X- chromosome regions o This happen
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