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GeneticsSubmitted to –
Dr Sapna sharma
Dept of Genetics
Presented by –
M sc Forensic science 4th sem
Roll no -1602
2/19/2017 1Deepak Saini
• 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.
Terms you should know
• CHROMOSOME: thread of DNA, made up of a string of
• 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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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 )
2/19/2017 4Deepak Saini
•Genes control the characteristics of living
•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,
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.
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sperm mother cell
ovum mother cell
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• 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
• 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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• In human,
es number 1
es 21 is the
In short, the 44 chromosomes are autosomes andes.
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• - 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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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
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• hereditary mutations or germline
• This type of mutation is present
throughout a person’s life in
virtually every cell in the body.
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• 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
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• 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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• 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
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• 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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• Different types of population genetics:
– Empirical population genetics: measures and
quantifies aspects of genetic variation in
– 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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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
• 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
• 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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Laid the first early groundwork the modern synthesis:
Charles Darwin 1809-1882
The Origin of Species
Alfred Russell Wallace 1823-1913
Thomas H. Huxley 1825-1895
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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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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
2/19/2017 35Deepak Saini
Ways to describe genetic structure of populations:
• Count individuals with one genotype and divide by total
number of individuals. Repeat for each genotype in the
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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Ways to describe genetic structure of populations:
• 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
2. Genotypic frequency method:
p = f(A) = (frequency of the AA homozygote) + (1/2 x frequency of the
p = f(a) = (frequency of the aa homozygote) + (1/2 x frequency of the Aa
2/19/2017 37Deepak Saini
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
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
2/19/2017 38Deepak Saini
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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• Independently discovered by Godfrey H. Hardy
(1877-1947) and Wilhelm Weinberg (1862-
• Explains how Mendelian segregation influences
allelic and genotypic frequencies in a population.
2/19/2017 40Deepak Saini
Allele Frequencies don’t change over generations
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.
2/19/2017 42Deepak Saini
• Slide share.in
• Dr ravi prakash ppt
• Genomics text book
2/19/2017 Deepak Saini 43