Searching for Answers in our Genome
- 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
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
o You can see whales and hippos share some of these insertions (they are closest
Detection of Alu Polymorphisms
- Electrophoresis: technique separating fragments by size (depending on what substrate
o A way to identify them, as DNA is negatively charged (and it will go towards the
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 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
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.
- The 23 chromosomes of the human haploid set can be divided into 22 autosomes and a
pair of sex chromosomes (X and Y).
- Two regions can be distinguished on the Y chromosome.
- The pseudoautosomal region, where recombination occurs between X and Y
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
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-
o This happen