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Discuss results of forensics analysis
Review mini satellites and microsatellites
Present Y chromosome study of human origins
and migration
Discuss one exam question
TPA section1
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+ -
1. Odd is sample
containing DNA.
Even is blank
control.
2. “+” means control
with DNA. “-”
means control
without DNA.
400bp
100bp
3. “+” on the gel
picture means
real band.
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400bp
100bp
TPA section2
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3
4
5
6
7
8 9 10 11 12 13 14 15 16 +
400bp
2. “+” means control
with DNA. “-”
means control
without DNA.
100bp
17 18 19 20 21 22 23 24 25 26 27 28 29 30
400bp
100bp
-
1. Odd is sample
containing DNA.
Even is blank
control.
+
-
3. “+” on the gel
picture means
real band.
DIS80 section1
1
2
3 4
5 6 7 8
9 10 11 12 1314 15 16
+ -
1. Odd is sample
containing DNA.
Even is blank
control.
400bp
2. “+” means control
with DNA. “-”
means control
without DNA.
100bp
17 18 19 20 21 22 23 24 25 26
400bp
100bp
27 28 29 30 31 32 +
-
3. “+” on the gel
picture means
real band.
DIS80 section2
1 2 3 4 5 6
7 8 9 10 11 12 13 14 15 16
+ -
1. Odd is sample
containing DNA.
Even is blank
control.
400bp
100bp
2. “+” means control
with DNA. “-”
means control
without DNA.
17 18 19
400bp
100bp
20 21 22 23 24
25 26 27 28 29 30
+
-
3. “+” on the gel
picture means
real band.
Up to 100bp repeats
Microsatellites have repeats of 2-5 bp
Tracing the dispersal of human populations
By analysis of polymorphisms in the
Non-recombining region of the Human
Y Chromosome
Underhill et al 2000 Nature Genetics 26: 358-361
Underhill et al 2001 Annals of Human Genetics 65: 43-62
Traditional paleoanthropological studies look at
where things that look and act like us first appeared
and when.
Underhill, Cavalli-Sforza and colleagues have used various
DNA polymorphisms to follow human evolution.
Phylogeography analyzes genetic diversity to predict time
to a Most recent common ancestor.
In addition, the location of populations with diverse alleles
Is used to predict the location of first appearance of
common ancestral genes.
Phylogeography assumes a correspondence between
Overall distribution of polymorphisms and past human
movements.
Underhill et al 2001
Sampled polymorphic loci on the Y chromosome to follow
Human evolution.
Sampled DNA from 1062 men.
Represent 52 indigenous populations
Distributed around the world.
In preliminary studies, they identified 218
Y-linked polymorphic loci. Most loci were biallelic –
Ancestral or derived allele.
After scoring each man’s DNA for all 218 loci,
they found 131 different haplotypes.
A haplotype represents a group of genes
that do not separate by recombination.
Each haplotype is the collection of alleles for
that non-recombining group of genes in an individual.
Examples include the human MHC locus,
The Fast Plant self incompatibility locus,
The non-recombining region of the mammalian
Y chromosome.
One approximately every 200-500 kb in the human genome.
NRY haplotypes from Jefferson family members
The differences between haplotypes is used to estimate
the time to the most recent common ancestor to be
60,000 years.
Using maximum parsimony analysis,
they grouped the haplotypes into 10 haplogroups
Great ape DNA used to make a root in the tree
The geographic distribution of the haplogroups indicates
how people migrated to colonize the whole world.
Maximum Parsimony Analysis:
Fewest changes to establish relationships
between all individuals.
Sample population with 4 biallelic loci:
ABCD
AB’CD
A’BCD
AB’C’D
AB’CD’
A’B’C’D
A’B’CD
ABCD
_____________________
AB’CD
A’BCD
_________
__________
AB’C’D
AB’CD’
A’BC’D
A’B’CD
Each step is one mutation from progenitor –
estimate time based on uniform mutation rate.
Maximum parsimony analysis of
polymorphisms in human Y chromosomes
Predicted time to common ancestor is 59,000 years.
95% confidence interval is 40,000 – 140,000 years.
Paleological evidence indicates modern humans
Spread throughout Africa 90,0000-130,000 years ago.
Estimates based on mitochondrial DNA also indicate
common ancestor 100,000-200,000 years ago.
Estimated time to most recent common ancestor
is based on the number of differences that distinguish
the haplotypes,
an assumed mutation rate
and an assumed model of population evolution
Caveots
Stable mutation rate
Selection
Unpredicted population bottlenecks
Y chromosome analysis fits with roughly with
paleological and mitochondrial DNA evidence.
Reveals more migration events than paleological record.
Estimates fairly early date to most recent common
ancestor.
Did our family replace other humans that existed earlier?
Y vs. Mitochondrial time to most recent common ancestor.
Reasons for the expansion of our single hominid
family are still being examined.
FOXP2 is a transcription factor that affects speech
Family with a known dominant mutation –
Problems with motor aspects of speech but also
Cognitive aspects
Molecular studies of variation at FOXP2 locus
Shows FOXP2 has significantly high rate of evolution
in hominid lineage – rapid substitutions comparing
Humans to chimps and other mammals
This analysis concludes that the Human FOXP2 allele
may have evolved less than 100,000 years ago.
Which marker is closest to the Gene
that controls the disease?
M1
A
R
M2
A R
R
M3
A?
A?
Distribution model assumes that genotypes of
modern indigenous people reflects early
migration routes
Caveots
Continuous gene flow
Selection effects
Effects of recent events such as migrations
Earlier studies with Mitochondrial DNA monitor
the female lineage of modern humans
Human genome sequence allowed identification of
stable haplotypes of autosomal genes.
These have recently also been used to trace the lineage
of modern humans
The time line is harder to determine and generally the
Estimated time to common ancestor is longer
Distribution patterns are harder to follow but are
Generally consistent with data from the NRY analysis.
100,000 years ago ancient humans filled Africa
Homo erectus had migrated all over Europe and Asia
Neanderthal man and Java man
Why did modern humans spread out and take over
all available niches?
One suggestion is FOXP2 mutation
Homo erectus
The first example of Homo erectus, known as "Java Man," was discovered
in Indonesia in 1893. Fossil remains of Homo erectus have since been
found throughout Africa and Asia, making it the first wide-ranging hominid.
Despite the primitive appearance of its skull, the erectus skeleton is very
similar to that of modern humans, although more robust (thicker and
heavier). Homo erectus was probably the first hominid to use fire.
1.8 mya - 300,000 years ago
first fossil found in 1893
Homo sapiens (archaic)
Also known as Homo heidelbergensis, this species has a brain that was larger
than H. erectus' and smaller than that of a modern human. The brain was
enclosed in a skull that was more rounded than H. erectus'. Fossil remains of
archaic Homo sapiens have been found in Africa and Europe.
500,000 - 200,000 years ago
first fossil found in 1921
Homo sapiens neanderthalensis
Averaging five and a half feet in height and possessing short limbs, Neanderthals
were well-adapted to living in a cold climate. Attached to their robust (thick and
heavy) bones were powerful muscles. The Neanderthal's brain was larger than
the brain of living humans, although its shape was longer from front to back
and not as rounded in the front.
230,000 - 30,000 years ago
first fossil found in 1856
Homo sapiens (modern)
Modern Homo sapiens, also known as Homo sapiens sapiens, have been around
for the past 120,000 years. Homo sapiens living about 40,000 years ago made
elaborate tools out of bone, antler, ivory, stone, and wood, and produced fine
artwork in the form of carvings and cave paintings.
120,000 years ago - present