2. G E N E T I C
Genetics is the study of genes, heredity and genetic
variations in living organisms.
Genes (Wilhelm Johannensen, 1909) – Ahereditaryfactorthat
Heredity - Thepassingofphenotypiccharactersfromparentstotheir
Genetic variation - It referthedifferencesbetweenindividualsor
The term “Genetics” wasf i
rst proposed by the English biologist
W illiam B ateson (1861 - 1926) in 1909.
Genetics is relevant to all f ields of biological disciplines
includes Me d i c i ne , A gri c ul t ure , A nt hro po l o gy,
Biochemistry, Microbiology, Biotechnology, Ecology,
Physiology and Psychology .
3. Mid 1800’s Discoverie
sFour major events in th
e mid-1800’sled directly
o the development of Modern Genetics.
● 1859: Charles Darwin
“The Origin o
Species” which describes the “Theory of Evolution” by
1866: Gregor Mendel publishes experiments in
“Plant Hybridization” which lays out the basic theory
of genetics. It is widely ignored until 1900.
1871: Friedrich Miescher isolates “Nucleic acid”
from pus cells.
1888: Waldeyer coined the term “Chromosomes”
4. Major Events in the 20 th
● 1900: Rediscovery of
work by Robert
H ugo de V ries, and E rich von T schermak .
1901: Hugo DeVries coined the term “Mutation”
1902: Archibald Garrod discovers that “Alkaptonuria
(Black urine and Black bone caused by mutation in HDG
Gene)”, a human disease, has a genetic basis.
1909: The term “Genetics” wasf i
rst proposed by the English
biologist William Bateson .
● 1909: The term “Gene” was f i
rst introducedby W ilhelm
1910: Genetics became an independent scientif i
c f i
with the study of the fruit f l
y (Drosophila melanogaster)
Thomas Hunt Morgan at Columbia University in New
1918: R . A . Fisher begins the study of quantitative
genetics by partitioning phenotypic variance into a genetic
d i t l t
5. ● 1926: Hermann J.
Mutation” in Drosophila and the mutationcan be inducedby
Roengten rays (X rays).
1928: F. Griﬃth proposed the “Transforming Principle”
which shows “DNA – as a Genetic material”.
● 1940: L ederberg and T atum
● 1941: C .
A uerbach a
J.M. R obson observed th
mutation inducing chemicals.
1941: Beadle and Tatum proposed “One Gene One
Enzyme Theory” (One gene is responsible for the formation
of one enzyme).
1944: Oswald Avery, Colin MacLeod and Maclyn
M c C a r t y show that DNA can transform bacteria,
demonstrating that DNA is the hereditary material.
6. ● 1947: Delbruck and
“Genetic Recombination” in
● 1952: H ersheyand
information is transferred by
1 9 5 3 : James Watso n and Fra nc i s C r i c k
determine the structure of the DNA molecule, which
leads directly to knowledge of how it replicates.
● 1955: F. Sanger determined
● 1966: Marshall Nirenberg solves
showing that 3 DNA bases code for one amino
1 9 7 2 : S tanley C o h e n and H e rb e r t Bo ye r
combine DNA from two different species in vitro,
then transform it into bacterial cells: f i
rst DNA cloning.
1 9 7 7 : Max am – G i l b e r t developed DNA
● 2001: Sequence of the entire
8. COMMON TERMINOLOGIES IN
Trait– Adistinguishingqualityofcharacteristics, typicallyone
belongingto aperson. Inscience, the word Trait refers to a
characteristic that iscaused byGenetics.
inant– Traitsthat are expressed.
Recessive– Traits that are covered up.
Alleles– Different formsofcharacteristics.
Homozygous– Two same Alleles.
Heterozygous- Two different Alleles.
Probability – Chances or percentages that something will
10. GREGOR MENDEL
Conducted his experiment with Pea (Pisum
sativumL.) plants because
Understood that somethingthat carried traits
from one generation to the next – Factor.
11. MENDEL’S EXPERIMENT WITH PEA PLANT
(Pisum sataivum L.)
Gregor Mendel was one of the f irst to apply an
experimental approachto the question of “inheritance”.
For seven years, Mendel bred pea plants and recorded
inheritance patternsin the offspring.
ParticulateHypothesisofInheritance- Characters of parents
passon to their offspring separate and distinct factors
(today called genes) that are responsible for inherited
Mendel probably chose to work with peas because they
are available in manyvarieties.
18. LAW OF INDEPENDENT ASSORTMENT
The principles that govern heredity were discovered byamonk
named Gregor Mendel inthe 1860's. One ofthese principles, now
called “Mendel’s Law of Independent Assortment”.
It isalso called as“Mendel’s Second Law” .
Mendel’s Law of Independent Assortment states that allele
pairs separate independently during the formation of gametes.
Thismeansthat traits are transmitted to offspring independently
of one another.
Mendel formulated this principle after performing Dihybrid
crosses between plants that differed in two traits, such asseed
color and pod color. After these plants were allowed to self
pollinate, he noticed that the same ratio of 9:3:3:1 appeared
among the offspring. Mendel concluded that traits are
transmitted to offspringindependently.
The image shows a true-breeding plant with the
dominant traits of green pod color (GG) and
yellow seed color (YY) being cross-pollinated with a
true breeding plant with yellow pod color (gg) and
green seeds (yy). The resulting offspring are all
heterozygous for green pod color and yellow seeds
Ifthe offspringare allowed to self pollinate, a 9:3:3:1
ratio willbe seeninthe next generation.
It is a cross between two pure organisms in order to
studythe inheritance ofasingle pair ofalleles.
It produces a phenotypic moho
hybrid ratio of 3: 1 in F2
It producesgenotypic ratio of1: 2: 1 inF2
22. DIHYBRID CROS
It isacrossbetween two pure organismsofaspecies
inorder to studythe inheritance oftwo pairsofalleles.
It produces a phenotypic di-hybrid
ratio of 9: 3: 3: 1 in F2
It producesgenotypic ratio of1 : 2 : 1 : 2 : 4: 2 : 1 : 2.
23. BACK CROSS AND TES
Back cross isthe mating process
dominant or recessive parent.
Test crossis the mating process between the
progeny andthe recessive parent.
Aback cross isthe breedingofan F1 backto a
homozygous individual(either dominant or recessive).
Atest cross involves breeding of ahomozygous
recessiveto the isolated trait.
24. GENOTYPE AND PHENOTYPE
Deﬁnition The genetic
of the genotype. An
to the information expressed and
contained on two observable trait.
alleles in the cell.
Examples DNA and Hair colour, Eye
Susceptibility to colour, Weight and
diseases other physical
Inheritance Inherited from
Cannot be inherited
25. Genotype Phenotype
Dependsupon The hereditary
given to an individual by
nt their parents
Contains All the hereditary
information of an
individual, even if
those genesare not
inedby Genotyping– usinga
biological assay, such
as PCR, to find out
what genesare on
an allele. (Inside the
26. ALLELE AND
“Allele”refers to “Aspecifi
c variation ofa gene” (Example -
Blueeyes, Green eyes, TypeAblood, Black skin and White
“Allele”also refers to “Different formsofcharacteristics”.
“Gene”refersto “AsectionofDNAthat controlsacertaintrait”
(Example - Eye color, Blood type and Skincolor).
Trait - Adistinguishingqualityofcharacteristics,typicallyone
belonging to aperson.