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POPULATION GENETICS AND HUMAN EVOLUTION
1. Hardy Weinberg principle states that in a population’s gene pool, the frequencies of
genotypes and alleles remain constant from one generation to the next unless if acted on
by other factors other than sexual recombination.
If a population has genotypes 𝐺𝐺, 𝑔𝑔 and 𝐺𝑔, then GG will represent 𝑝2. 𝑔𝑔 Will
represent 𝑞2 and 𝐺𝑔 will represent 2𝑝𝑞 .
The factors which can disturb the Hardy Weinberg equilibrium are as follows
Natural selection- This causes changes in gene frequencies and therefore interferes with
the equilibrium
Genetic drift – This takes place when the frequencies of alleles grow higher or lower by
chance. It generally occurs in populations that are small
Non-random mating- causes disruption of the Hardy Weinberg equilibrium as a result of
changes in gene frequencies
Gene flow – This is where transfer of genes takes place as a result of breeding between
two different populations. New alleles are transferred to either of the populations
Mutations – These also introduce new alleles into a population
Hardy Weinberg principle represents an ideal state that if not disrupted by other forces
(above) maintains constant genotypes and alleles.
There are influences that deviate from the Hardy Weinberg principle. These are
Inbreeding which changes genotype proportions. Because inbreeders are related, they
are more likely to have matching alleles for one characteristics.
Small population sizes- the gamete sampling and fertilization to create zygotes leads to
random error in small populations. This leads to deviation from the Hardy Weinberg
principle
2. DNA profiling refers to the process of obtaining a specific DNA pattern from a tissue,
blood or any other bodily sample. DNA in different individuals are identical in most of
their sequences except a few variable polymorphic regions. DNA profiling is performed
in a series of steps as indicated below.
DNA sample collection
First, a DNA sample is obtained from any body part. It could obtained from blood,
semen, saliva, hair roots or any part of interest. Scientists or even police officers obtain
the samples from the scenes of crime. The DNA can also be obtained directly from an
individual using mouth swab or even nasal swab.
DNA Extraction
DNA is then extracted from the cell nucleus by addition of chemicals which break the
cells open. The DNA is then isolated from other components of the cell
DNA Copying
Since only small amount of DNA is extracted for forensic analysis, the short tandem
repeats in every genetic locus are amplified using a technique such as Polymerase Chain
Reaction (PCR). This provides enough quantity for profiling. Specific primers are used in
Polymerase Chain Reaction (PCR), and this attaches a tag on the Short Tandem Repeats
that have been copied. The tag is, in most cases fluorescent for easier detection
Determination of Short Tandems Repeat size
At every genetic locus, the size of each Short Tandem Repeat (STR) is determined by use
of a genetic analyzer, which separates the DNA that has been copied (by a technique of
gel electrophoresis). The genetic analyzer also detects the fluorescent at every Short
Tandem Repeat
Profile Matching
A calculation of the number of times a given nucleotide sequence has been repeated can
then be done. This done based on the size of Short Tandem Repeat (STR). This
information is useful in determining whether or not a given sample is from a particular
person. If two profiles are similar in their sequences there is a high chance that they come
from the same source.
Uses of DNA profiling.
a)
b)
c)
d)
To link a suspect to a particular crime
To identify victims of disaster
To show a family relationship
For paternity identification to determine if the alleged father is the true biological
father of the child
e) To tell whether a given set of twins are Identical or fraternal
f) For immigration purposes to show any proof of relatedness.
3. Other than the mentioned diseases, another example of a balanced polymorphism is TaySachs disease. This is a genetic disease in which there is abnormal accumulation of
neuronal lipids. The alleles for Tay Sachs disease are common within certain populations
such as the Ashkenazi. It has been hypothesized that the allele for this disease confers
resistance to Mycobacterium tuberculosis, which causes TB. The carriers of the gene for
Tay Sachs Disease produce beta- subunit if hexosaminidase enzyme in increased
quantities. The beta sub-unit of the enzyme increases a person’s defense against
Tuberculosis. The enzyme Beta hexosaminidase is therefore cytotoxic to M. tuberculosis
Drugs which maintain or up-regulate the beta hexosaminidase may be useful in treating
drug resistant tuberculosis
4. Genetic ancestry testing is not completely accurate and reliable. Most of the genetic
ancestry tests only seem to be giving better information on Indians, Europeans or
Africans but not on the Ancestry of Native Americans. This is because the native
Americans have not participated in these genetic ancestry testing and scientists tend to
make guesses that are not very accurate. In making comparisons of genetic information
among populations the scientists tend to say that the Americans are more similar to the
Indians compared to other populations. Besides there are no genetic test that can
determine affiliations in terms of tribes.Neither are genetic markers to prove the Native
American ancestry.