forensic science

1. Human Genetics
And Population
GeneticsSubmitted to –
Dr Sapna sharma
Dept of Genetics
MDU Rohtak
Presented by –
Deepak Saini
M sc Forensic science 4th sem
Roll no -1602
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2. Genetics
• Human genetics- scientific study of human
variation and Heredity
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.Genetics is the study of genes, genetic variation, and
heredity in living organisms. It is generally considered
a field of biology, but intersects frequently with many
other life sciences and is strongly linked with the study
of information systems.

3. Terms you should know
• CHROMOSOME: thread of DNA, made up of a string of
genes.
• GENE: a length of DNA that is the unit of heredity and
codes for a specific protein. A gene may be copied and
passed on to the next generation.
• ALLELE: any of two or more alternative forms of a gene.
• HAPLOID NUCLEUS: a nucleus containing a single set of
unpaired chromosomes (e.g. sperm and egg)
• DIPLOID NUCLEUS: a nucleus containing two sets of
chromosomes (e.g. in body cells)
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4. Terms you should know:
• GENOTYPE: genetic makeup of an organism in term of the
alleles present ( e.g. Tt or GG).
• PHENOTYPE: physical or other features of an organism
due to both its genotype and its environment (e.g. tall
plant or green seed)
• HOMOZYGOUS: having two identical alleles of a particulat
gene (e.g. TT or gg).Two identical homozygous individuals
that breed together will be pure-breeding.
• HETEROZYGOUS: having two different alleles of a
particular gene (e.g. Tt or Gg), not pure- breeding.
• DOMINANT: an allele that is expresed if it is present
(e.g. T or G)
• RECESSIVE: an allele that is only expresses when there is
no dominant allele of the gene present. ( e.g t or g )
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5. •Genes control the characteristics of living
organisms
•Genes are carried on the chromosomes
•Chromosomes are in pairs, one from each parent
•Genes are in pairs
•Genes controlling the same characteristics occupy
identical positions on corresponding chromosomes
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Heredity is the genetic information passing
for traits from parents to their offspring, either
through asexual reproduction or sexual reproduction.
.This is the process by which an
offspring cell or organism acquires or becomes
predisposed to the characteristics of its parent cell or
organism. Through heredity, variations exhibited by
individuals can accumulate and cause
some species to evolve through the natural
selection of specific phenotype traits.
-The study of heredity in biology is called genetics,

7. In most populations of animals there are approximately equal
numbers of males and females.
This is the result of a pair of chromosomes; the sex chromosomes
called the X and Y chromosomes.
The X and Y chromosomes are a homologous pair but in many
animals the Y chromosome is smaller than the X.
Females have two X chromosomes in their cells.
Males have one X and one Y in their cells.
At meiosis, the sex chromosomes are separated so the the gametes
receive only one: either an X or a Y.
Sex chromosomes
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8. X
Y
X
X
X
Y
X
X
X
X
X
X
X
Y
X
Y
sperm mother cell
ovum mother cell
meiosis
fertilization
female
female
male
male
Sex ratio
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9. • People have been fascinated at how children will
resemble their parents and vice versa.
• As years went by, scientists began to search for
more information on how these traits are passed
on.
• The passing of traits from parents to offspring is
HEREDITY and the science that deals with the
study of heredity is GENETICS.
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10. • In human,
chromosom
es number 1
is the
biggest
containing
8,000 genes
and
chromosom
es 21 is the
smallest
with 300
genes.
In short, the 44 chromosomes are autosomes andes.
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11. Mutation
• - is a change of the nucleotide sequence of the
genome of an organism, virus, or extra
chromosomal genetic element.
• Mutations result from errors during DNA
replication or other types of damage to DNA.
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12. Types of Mutation
•Substitution
•Insertion
•Deletion
•Frameshift
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13. Substitution
A substitution is a mutation
that exchanges one base for
another (i.e., a change in a
single "chemical letter" such as
switching an A to a G).
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15. Insertion
Insertions are
mutations in which extra
base pairs are inserted
into a new place in the
DNA.
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17. Inversion
a DNA sequence of
nucleotides is reversed.
Inversions can occur among a
few bases within a gene or
among longer DNA sequences
that contain several genes.
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19. Deletion
Deletions are
mutations in which a
section of DNA is lost, or
deleted.
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21. Frameshift
Since protein-coding DNA is
divided into codons three bases
long, insertions and deletions
can alter a gene so that its
message is no longer correctly
parsed.
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23. Gene Mutation
is a permanent change in the
DNA sequence that makes up a
gene. Mutations range in size from
a single DNA building block (DNA
base) to a large segment of a
chromosome.
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24. Inherited
• hereditary mutations or germline
mutations
• This type of mutation is present
throughout a person’s life in
virtually every cell in the body.
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25. Acquired
• or somatic mutations
• occur in the DNA of individual cells
at some time during a person’s life.
• caused by environmental factors
• cannot be passed on to the next
generation.
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26. Natural cause
• DNA fails to copy accurately
–when a cell divides, it makes a
copy of its DNA and sometimes
the copy is not quite perfect.
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27. External Influences/Mutagens
• In genetics, a mutagen is a
physical or chemical agent that
changes the genetic material,
usually DNA, of an organism and
thus increases the frequency of
mutations above the natural
background level.
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29. Population genetics
• Investigates genetic variation among individuals
within groups (populations, gene pools).
• Examines the genetic basis for evolutionary
change and seeks to understand how patterns
vary geographically and through time.
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30. • Different types of population genetics:
– Empirical population genetics: measures and
quantifies aspects of genetic variation in
populations.
– Theoretical population genetics: explains variation
in terms of mathematical models of the forces that
change allele frequencies (genetics drift, selection,
gene flow, etc.).
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31. Types of questions studied by population geneticists:
• How much variation occurs in natural populations, and
what processes control the variation observed?
• How does geography and dispersal behavior shape
population structure?
• What forces are responsible for population differentiation
and how do they affect genetic diversity?
• Mutation  genetic diversity
• Selection  genetic diversity
• Genetic drift  genetic diversity
• Migration  genetic diversity
• Non-random mating  genetic diversity
• Recombination  genetic diversity2/19/2017 31Deepak Saini

32. Population Genetics:
• One of the oldest and richest examples of success of
mathematical theory in biology.
• Provided synthesis of Mendelian genetics and
Darwinian natural selection in the first part of the 20th
century  “modern synthesis”.
• Modern synthesis is the foundation for modern
evolutionary biology and population genetics.
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33. Laid the first early groundwork the modern synthesis:
Charles Darwin 1809-1882
The Origin of Species
Alfred Russell Wallace 1823-1913
“Wallace’s Line”
Thomas H. Huxley 1825-1895
“Darwin’s Bulldog”
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34. Theoretical/mathematical population geneticists:
Ronald A. Fisher 1890-1962
The Genetical Theory of Natural Selection
J. B. S. Haldane 1892-1964
The Causes of Evolution
Sewall Wright 1889-1988
Evolution and the Genetics of Populations - 4 vol.
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35. Architects the modern synthesis, extended theoretical work of Fisher, Haldane, and
Wright to real organisms:
Theodosius Dobzhansky 1900-1975
Genetics and the Origin of Species
Julian Huxley 1887-1975
Evolution: The Modern Synthesis
Ernst Mayr 1904-2005
Systematics and the Origin of Species
“Biological Species Concept”
George G. Simpson 1902-1984
Tempo and Mode in Evolution
George L. Stebbins 1906-2000
Variation and Evolution
in Plants
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36. Ways to describe genetic structure of populations:
Genotypic frequency
• Count individuals with one genotype and divide by total
number of individuals. Repeat for each genotype in the
population:
f(BB) = 452/497 = 0.909
f(Bb) = 43/497 = 0.087
f(bb) = 2/497 = 0.004
Total = 1.000
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37. Ways to describe genetic structure of populations:
Allelic frequency
• Allelic frequencies offer more information than genotypic
frequencies and can be calculated in two different ways:
1. Allele (gene) counting method:
p = f(A) = (2 x count of AA) + (1 count of Aa)/ 2 x total number of
individuals
2. Genotypic frequency method:
p = f(A) = (frequency of the AA homozygote) + (1/2 x frequency of the
Aa heterozygote)
p = f(a) = (frequency of the aa homozygote) + (1/2 x frequency of the Aa
heterozygote)
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38. Allelic frequencies with multiple alleles:
Example: A1, A2, and A3
p = f(A1) = (2 x A1A1) + (A1A2) + (A1A3)/2 x total individuals
q = f(A2) = (2 x A2A2) + (A1A2) + (A2A3)/2 x total individuals
r = f(A3) = (2 x A3A3) + (A1A3) + (A2A3)/2 x total individuals
Or
p = f(A1) = f(A1A1) +f(A1A2)/2 + f(A1A3)/2
q = f(A2) = f(A2A2) + f(A1A2)/2 + f(A2A3)/2
r = f(A3) = f(A3A3) + f(A1A3)/2 + f(A2A3)/2
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39. Allelic frequencies at X-linked loci:
Females have 2 X-linked alleles, and males have 1 X-linked allele.
p = f(XA) = (2 x XA XA females) + (XA Xa females) + (XA Y males)/
(2 x # females) + (# males)
q = f(Xa) = (2 x Xa Xa females) + (XA Xa females) + (Xa Y males)/
(2 x # females) + (# males)
If number of females and males are equal:
p = f(XA) = 2/3[f(XAXA) +1/2f(XAXa)] + 1/3f(XAY)
q = f(Xa) = 2/3[f(XaXa) +1/2f(XAXa)] + 1/3f(XaY)
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40. Hardy-Weinberg law:
• Independently discovered by Godfrey H. Hardy
(1877-1947) and Wilhelm Weinberg (1862-
1937).
• Explains how Mendelian segregation influences
allelic and genotypic frequencies in a population.
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41. Hardy-Weinberg Equilibrium
Allele Frequencies don’t change over generations

42. Assumptions:
1. Population is infinitely large, to avoid effects of genetic
drift (= change in genetic frequency due to chance).
2. Mating is random (with regard to traits under study).
3. No natural selection (for traits under study).
4. No mutation.
5. No migration.
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43. Referecnes
• Wikkipedia.net
• Slide share.in
• Dr ravi prakash ppt
• Genomics text book
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