LOYOLA HIGH SCHOOL

PATNA

AISSCE BIOLOGY BOARD PROJECT 2024-25

“FROM MENDEL TO EPIGENETICS:

HISTORY OF GENETICS”…………….

NAME:-- ABHIMANYU GUPTA

CLASS:--- XII ‘A’

ROLL NO:--- 03

BOARD ROLL NO:---

 CERTIFICATE
This is to certify that ABHIMANYU GUPTA
bearing Board Roll No.
is a student of class XII'A' (03).
He has successfully completed his biology
project titled "Various Tools and Techniques of
Biotechnology" as per guidelines of CBSE for
the academic year 2024-25 under the guidance
of Dr. Sweta Sinha.
It is further certified that this project is the
individual and bonafide work of the candidate.

---------------------------- --------------------------
SIGNATURE OF SIGNATURE OF
INTERNAL EXAMINER EXTERNAL EXAMINER
 ACKNOWLEDGEMENT
I would like to express my sincere gratitude to all those
who contributed for the successful completion of this
project. This project would not have been possible
without their support, guidance, and encouragement.

First and foremost, I would like to thank my principal and

my biology teacher Dr. Sweta Sinha for their invaluable
guidance and constant support throughout the project.
Their feedback and expertise were instrumental in
shaping the direction of my work.

I am also grateful to my classmates and friends for their

inputs, motivation and wishful co- operation which
helped me refine my idea and make this project more
comprehensive.

Lastly, I want to thank my family for their unwavering

support, patience and understanding during the entire
project process.
CONTENTS
G.J MENDEL :---- FATHER OF
GENETICS
------BIOGRAPHY-------

Gregor Johann Mendel (1822-1884) was an

Augustinian priest and scientist who established the
fundamental laws of heredity and is known as the
"Father of Genetics":

• Birth and family

Mendel was born in Hynčice, Moravia, in what is
now the Czech Republic on July 22, 1822. He
came from a poor farming family and struggled to
pay for his education.

• Education
Mendel attended local schools and studied
philosophy at the University of Olomouc. He also
studied theology at the Brünn Theological College
and was ordained as a priest in 1847.
• Monastery life
Mendel joined the Augustinian Order at St.
Thomas Monastery in Brünn, where he taught
natural history and physics at the Brünn Modern
School. The monastery was a center of scientific
and cultural interest, with a library, botanical
garden, and herbarium.

• Experiments
From 1856 to 1863, Mendel conducted
experiments on pea plants, growing over 10,000
plants and tracking their progeny. He discovered
that each plant had two characters of heredity and
that each parent could only pass one of its
characters on to its offspring.

• Laws of heredity
Mendel's experiments led to the establishment of
his Laws of Heredity, which include the Law of
Segregation, the Law of Independent Assortment,
and the Law of Dominance.

• Recognition
Mendel's work was not widely recognized during
his lifetime, but was rediscovered in 1900.
• Gregor Johann Mendel is known as the 'Father of
Genetics'.

• Gregor Mendel, conducted hybridisation

experiments on garden peas for seven years (1856-
1863).
Proposed the laws of inheritance in living
organisms.

• During Mendel's investigations into inheritance

patterns it was for the first time that statistical
analysis and mathematical logic were applied to
problems in biology.

• Mendel investigated characters in the garden pea

plant that were manifested as two opposing traits,
e.g., tall or dwarf plants, yellow or green seeds.

• Mendel selected 14 true-breeding pea plant

varieties, as pairs which were similar except for
one character with contrasting traits. Some of the
contrasting traits selected were smooth or
wrinkled seeds, yellow or green seeds, inflated
(full) or constricted green or yellow pods and tall or
dwarf plants.
 MENDELIAN GENETICS &
VARIATION
➢ All living organisms reproduce.
It results in the formation of offspring of the
same kind.
The resulting offspring most often do not
totally resemble the parent.
Siblings sometimes look so similar to each
other or sometimes even so different.

➢ Genetics: It is a branch of biology which

deals with the inheritance, as well as the
variation of characters from parents to
offspring.

➢ Inheritance: Inheritance is the process by

which characters are passed on from parent
to progeny; it is the basis of heredity.

➢ Heredity: Heredity is the transmission of

characters from parents to their offsprings.

➢ Variation: Variation is the degree by which

progeny differ from their parents.
 ➢ Environmental variation: These are aquired
and non heritable.

➢ Hereditary variations: These are genetical

and inheritable.

ANCIENT ARTIFICAL SELECTION AND

DOMESTICATION OF ORGANISM……………….

Humans knew from as early as 8000-1000 B.C. that

one of the causes of variation was hidden in sexual
reproduction. They exploited the variations that
were naturally present in the wild populations of
plants and animals to selectively breed and select for
organisms that possessed desirable characters.
For example, through artificial selection and
domestication from ancestral wild cows, we have
well known Indian breeds, e.g.… Sahiwal cows in
Punjab.
We must, however, recognise that though our
ancestors knew about. the inheritance of characters
and variation, they had very little idea about the
scientific basis of these phenomena.
 TERMINOLOGIES
➢ Phenotype: The external appearance of an
organism due to the influence of genes and
environmental factors.

➢ Genotype: The genetic constitution of an

individual responsible for the phenotype.

➢ Phenotypic ratio: The correct proportion of

phenotype in population.

➢ Genotypic ratio: The correct proportion of

genotype in population.

➢ Homozygous: The individual heaving

identical genes in an allelic pair for a character.
Ex: TT, tt.

➢ Heterozygous: The individual heaving un-

identical genes in an allelic pair for a character.

➢ Dominant gene: The gene that expresses its

character in heterozygous condition.
➢ Recessive: The gene that fails to express its
character in heterozygous condition.

➢ Hybrid: The progeny obtained by crossing

two parents that differ in characters.

➢ Back cross: The cross between F1 hybrid

and one of its parents.

➢Test cross: The cross between hybrid and its

homozygous recessive parent. It is used to
identify the genotype of the hybrid.
 Why Mendel selected
pea plant??........
➢ Pure variety are available.

➢ Pea plants are easy to cultivate.

➢ Life cycle of plants are only few

months. So that result can be got early.

➢ Contrasting trait are observed.

➢ Flowers are bisexual and normally

self pollinated.

➢ Flowers can be cross pollinated only

manually.

➢ Hybrids are fertile.

Seven pairs of contrasting traits in
pea plant studied by G.J Mendel………
o Inheritance of One
Gene..
▪ Inheritance of one gene can be explained by
monohybrid cross.
▪ The cross between two parents differing in
one pair of contrasting character is called
monohybrid cross.
▪ Crossed tall & dwarf pea plants- Collected
seeds & grew to generate first hybrid
generation/ Filial generation/F1.
▪ F1 plants- Tall & none were dwarf.
▪ For other traits also- F1 generation
resembled only one parent & trait of other
parent were not shown.
▪ Self pollinated F1 - Filial 2 generation/F2.
▪ F2 generation- 1/4th were dwarf & 3/4th
tall- identical to parents.
▪ F1 generation one parent trait shown & F2
both parent trait shown in the ratio- 3:1 &
no blending were seen.
▪ Mendel proposed- Something is stably being
passed to the next generation through
gametes 'factors' - genes.
▪ Genes/factors- unit of inheritance, contain
the information required to express
particular trait.
▪ Genes which code for pair of contrasting
trait- alleles.
▪ Alphabetical symbols were used; T-Tall, t-
dwarf
▪ Plants pair of alleles for height- TT, Tt & tt
▪ Mendel proposed- true breeding tall or
dwarf plant- identical or homozygous allele
pair of TT or tt (genotype)
▪ Descriptive term tall or dwarf- phenotype.
▪ Mendel found phenotype of heterozygote Tt
of F1 was same as parent with TT &
proposed, in a pair of dissimilar factors one
dominates the other & hence called
dominant (T) & recessive (t).
Figure :---- inheritance of one gene
 Punnett Square:---
▪ Production of gametes & formation of
zygotes.

▪ Developed by- British scientist Reginald C.

Punnett.

▪ Graphical representation- calculate

probability of possible genotypes in
genetic cross.

Gametes- on two sides, top row & left columns.

MENDELIAN LAWS OF INHERITANCE:---
❖ PRINCIPLE OF MENDELIAN
INHERITANCE….

I) Law of Dominance:---
When two different alleles are present,
only one is dominant and will be
expressed.

Characters are controlled by discrete units

called Factors that occurs in pair.

In a dissimilar pair of factors one member

of the pair dominates (dominant) the
other (recessive).

Used to explain the expression of only one

of the parental characters in monohybrid
cross (F1) & expression of both in F2. Also
explains proportion 3:1 in F2.
II) Law of Segregation:---

The two alleles for each gene are placed in

different gametes.

It states that, 'when a pair of factors for a

character brought together in a hybrid,
they segregate (separate) during the
formation of gametes.

Alleles do not blend & both characters

recovered in F2 & one in F1

Factors which is present in parent

segregate & gametes receives only one of
two factors.

Homozygous parent- one kind gamete

Heterozygous parent- two kind gamete

each one have one allele with equal
proportion.
 III) Law of Independent Assortment:---

The inheritance of one gene doesn't affect the

inheritance of any other gene.

Mendel's law of independent assortment states

that the alleles of two (or more) different genes
get sorted into gametes independently of one
another.

In other words, the allele a gamete receives for

one gene does not influence the allele received
for another gene.
INHERITANCE OF ONE GENE
A) Incomplete Dominance:---
• Correns discovered Incomplete dominance in
Merabilis jalapa.
• It is also called partial dominance, semi
dominance..
• The inheritance in which allele for a specific
character is not completely dominant over
other allele is called Incomplete dominance.
• Snapdragon or Antirrhinum sp.- Cross
between true breed red flower (RR) & white
flower (rr), F1 generation- Pink (Rr) & after self
pollination in F2 generation-1 (RR) Red: 2 (Rr)
Pink: 1 (rr) white
• Genotype ratio same as Mendelian cross &
Phenotype ratio different than Mendelian
cross.
Ex snapdragon. (Dog flower plant)
B) CO-DOMINANCE:---
• Both the alleles for a character are dominant
and express its full character is called co-
dominance.

• Ex AB blood group of human being. Blood

group in humans are controlled by 3 alleles of
a gene I.
• They are IA, IB and i.
The ABO locus is located on chromosome 9.
IA is responsible for production of antigen -A.
IB is responsible for production of antigen -B.
i does not produces any antigen.
IA and I are co-dominant and dominant over i.
INHERITANCE OF TWO
GENE:--
•Mendel's 2nd law or Law of Independent
Assortment:

• It states that, factors for different pairs of

contrasting characters in a hybrid assorted
(distributed) independently during gamete
formation.

• Mendel's 2nd law can be explained by dihybrid

cross.

Dihybrid cross: The cross between two parents,

which differs in two pairs of contrasting
characters.
 Note point.....
• Mendel work published on 1865 but remain
unrecognized till 1900.
❖ Reasons for that:
1. Lack of communication.
2. Concept of genes / factors- clear.
3. Mathematical approach for biology was not
accepted.
4. No proof for existence of factors.
 A) Chromosomal Theory of
Inheritance:--

• It was proposed by Walter Sutton and Theodore

Boveri.
• They work out the chromosome movement during
meiosis.
• The movement behavior of chromosomes was
parallel to the behavior of genes. The chromosome
movement is used to explain Mendel's laws
• The knowledge of chromosomal segregation with
Mendelian principles is called chromosomal theory
of inheritance.
• According to this, Chromosome and genes are
present in pairs in diploid cells.
• Homologous chromosomes separate during
gamete formation (meiosis)
• Fertilization restores the chromosome number to
diploid condition.
• Thomas Hunt Morgan and his colleagues
conducted experimental verification of
chromosomal theory of inheritance.
Morgan worked with tiny fruit flies, Drosophila
melanogaster because:---
• He selected Drosophila because,
• It is suitable for genetic studies.
Grown on simple synthetic medium in the
laboratory.
• They complete their life cycle in about two weeks.
• A single mating could produce a large number of
progeny flies.
• Clear differentiation of male and female flies
Many types of hereditary variations can be seen
with low power microscopes.
B)Linkage and recombination:---
Linkage and recombination are phenomena that describe
how genes are inherited:
Linkage…
Involves the inheritance of two or more genes that are
linked together in the same combination for more than
two generations. The genes remain on the same
chromosome.
Recombination…
Involves the exchange of genetic material between
different organisms, leading to offspring with a
combination of traits. This occurs during crossing over
during meiosis.
POLYGENIC INHERITANCE
This happens when multiple genes control a single trait,
or characteristic, in an organism. It's also known as
multiple gene inheritance or quantitative inheritance.

Here are some characteristics of polygenic inheritance:---

❖ Multiple genes: The genes that control
polygenic inheritance are called polygenes. Each
gene has a small effect on the phenotype, so it's
hard to detect the effect of a single gene.
❖ Additive effect: Each allele has a cumulative or
additive effect.
❖ Continuous variation: The phenotype of a trait
varies continuously.
❖ Complex pattern: The pattern of polygenic
inheritance is complex, making it difficult to predict
the phenotype.
o Examples of polygenic inheritance in humans include
height, skin color, eye color, and weight. In plants,
examples include green color in wheat and white
spotting in mice.
Polygenic and environmental factors contribute to
chronic diseases like coronary heart disease, cancer,
diabetes mellitus, asthma, gout, schizophrenia, and
osteoporosis.
PLEIOTROPY
The effect of a gene on a single phenotype or trait.

There are however instances where a single gene

can exhibit multiple phenotypic expression.
Such a gene is called a pleiotropic gene.

The underlying mechanism of pleiotropy in most

cases is the effect of a gene on metabolic pathways
which contribute towards different phenotypes.

An example of this is the disease phenylketonuria,

which occurs in humans.

The disease is caused by mutation in the gene that

codes for the enzyme phenyl alanine hydroxylase
(single gene mutation).
This manifests itself through phenotypic expression
characterised by mental retardation and a
reduction in hair and skin pigmentation.
SEX DETERMINATION
Henking (1891) traced specific nuclear structure
during spermatogenesis of some insects.

• 50% of the sperm received these specific

structures, whereas 50% sperm did not receive it.
• He gave a name to this structure as the X-body.
• This was later on named as X-chromosome.

Sex determination is the biological process that

determines the sex of an organism.

Note:----
Humans use XX-XY method but other organisms
may use different methods of sex determination,
such as the XX-X0 method, which is used in
roundworms and insects. For some organisms,
environmental factors and the temperature inside
the egg may also play a role in sex determination.
--------------
XX-XY method:---

In humans, the sex of a baby is determined by the

type of sperm that fertilizes the egg.
In humans, females have XX chromosomes and
males have XY chromosomes.
During gamete formation, half of sperm receive an X
chromosome and half receive a Y chromosome.
When an X-containing sperm fertilizes an egg, the
baby is female.
When a Y-containing sperm fertilizes an egg, the
baby is male.

Genetic makeup: The genetic makeup of the sperm

determines the sex of the baby.

Chances: There is a 50-50 chance of having a male

or female fetus.
XX-XY Type:---
• Sex determination in insects and mammals
• In this type both male and female has same
number of chromosomes.
• Female has autosomes and a pair of X
chromosomes. (AA+ XX)
• Male has autosomes and one large 'X'
chromosome and one very small 'Y- chromosomes.
(AA+XY)
• In this type male is heterogamety and female
homogamety.

XX-XO Type:---

Sex-determination of grass hopper:

The grasshopper contains 12 pairs or 24
chromosomes. The male has only 23 chromosome.
• All egg bears one 'X' chromosome along with
autosomes.
Some sperms (50%) bear's one 'X' chromosome and
50% do not.
Egg fertilized with sperm having 'X' chromosome
became female (22+XX).
Egg fertilized with sperm without 'X' chromosome
became male (22 + XO).

ZZ-ZW Type:---

Sex determination in birds :

In this type female birds has two different sex
chromosomes named as Z and W.
Male birds have two similar sex chromosomes and
called ZZ.
In this type of sex determination female is
heterogamety and male is homogamety.
Sex Determination in Honey Bee:---
The sex determination in honey bee is based on the
number of sets of chromosomes an individual
receives.
An offspring formed from the union of a sperm and
an egg develops as a female (queen or worker), and
an unfertilised egg develops as a male (drone) by
means of parthenogenesis. This means that the
males have half the number of chromosomes than
that of a female.
The females are diploid having 32 chromosomes
and males are haploid, i.e.. having 16 chromosomes.
This is called as haplodiploid sex-determination
system and has special characteristic features such
as the males produce sperms by mitosis they do not
have father and thus cannot have sons, but
have a grandfather and can have grandsons.
MUTATION
Phenotypic variation occurs due to change in gene
or DNA sequence is called mutation. The organism
that undergoes mutation is mutant.

• Phenomenon which result in alternation of DNA

sequence & result in change in genotype &
phenotype :----

1. Loss (deletion) or gain (insertion/duplication) of a

segment of DNA results in alteration in
chromosomes- abnormalities/ aberrations-
Chromosomal aberrations.

2. Gene Mutations: The mutation takes place due to

change in a single base pair of DNA is called gene
mutation or point mutation. E.g. Sickle cell anemia.

3. Frame shift mutations: Deletion or insertions of

base pairs of DNA is called frame shift mutations.
GENETIC DISORDERS
Genetic disorders grouped into two categories -
1. Mendelian Disorder
2. Chromosomal Disorder

Pedigree Analysis:---
• The study of inheritance of genetic traits in several
generations of a family is called the pedigree
analysis.

Pedigree study- strong tool of human genetics to

trace inheritance of specific
trait/abnormality/diseases.

Pedigree analysis of inheritance of a traits is

represented in family tree.
• It helps in genetic counseling to avoid genetic
disorders.
 1. Mendelian Disorders:---
• Mendelian disorders are mainly determined by
alteration or mutation in the single gene.
• It obey the principle of Mendelian inheritance
(principles of inheritance) during transmission from
one generation to other.
• Mendelian disorder- traced in family by pedigree
analysis
• E.g. Haemophilia, Colorblindness, Cystic fibrosis,
Sickle cell anemia, Phenylketonuria, Thalesemia etc.
• Dominant or recessive- pedigree analysis.
• Trait may linked to sex chromosome, Eg.
Haemophilia.
• X-linked recessive trait- transmitted from carrier
female to male progeny.

They are the form of genetic disorder that develops as a

result of changes in one gene or anomalies in the
genome. A disorder like this can be seen from birth and
discovered through family lineage and the genealogical
record. A mutation at a single genetic site causes
Mendelian diseases.
Few examples of the Mendelian disorder in humans are...
A) Colour Blindness…..
It is a sex-linked recessive disorder due to defect in either
red or green cone of eye resulting in failure to
discriminate between red and green colour.
This defect is due to mutation in certain genes present in
the X chromosome.
It occurs in about 8 per cent of males andonly
about 0.4 per cent of females.
This is because the genes that lead o red-green colour
blindness are on the X chromosome.
Males have only one X chromosome and females have
two.
The son of a woman who arries 2022-23 90 BIOLOGY the
gene has a 50 per cent chance of being colour blind.
The son of a woman who carries 2022-23 90 BIOLOGY the
gene has a 50 per cent chance of being colour blind.
Its effect is suppressed by her matching dominant normal
gene.
B)Haemophilia…..
This is a type of sex-linked recessive disorders. According
to the genetic inheritance pattern, the unaffected carrier
mother passes on the haemophilic genes to sons.
It is a very rare type of disease among females because
for a female to get the disease, the mother should either
be hemophilic or a carrier but the father should be
haemophilic.
This is a disorder in which blood doesn’t clot normally as
the protein which helps in clotting of blood is affected.
Therefore, a person suffering from this disease usually
has symptoms of unexplained and excessive bleeding
from cuts or injuries.
This type of genetic disorder is caused when the affected
gene is located on the X chromosomes. Therefore, males
are more frequently affected.

C) Sickle-cell anaemia……
This is a type of autosomal recessive genetic disorder.
According to Mendelian genetics, its inheritance pattern
follows inheritance from two carrying parents.
It is caused when the glutamic acid in the sixth position
of the beta-globin chain of haemoglobin molecule is
replaced by valine. The mutant haemoglobin molecule
undergoes a physical change which changes the
biconcave shape into the sickle shape.
This reduces the oxygen-binding capacity of the
haemoglobin molecule.

D) Phenylketonuria…..
This genetic disorder is autosomal recessive in nature.
It is an inborn error caused due to the decreased
metabolism level of the amino acid phenylalanine.
In this disorder, the affected person does not have the
enzyme that converts phenylalanine to tyrosine. As a
result, phenylalanine accumulation takes place in the
body and is converted into many derivatives which result
in mental retardation.

E) Thalassemia……
This is a type of disorder in which the body makes an
abnormal amount of haemoglobin. As a result, a large
number of red blood cells are destroyed that leads to
anaemia.
It is an autosomal recessive disease.
Facial bone deformities, abdominal swelling, dark urine
are some of the symptoms of thalassemia.
2. Chromosomal Disorders:----
• The chromosomal disorders on the other hand are
caused due to absence or excess or abnormal
arrangement of one or more chromosomes.
• Failure of segregation of chromatids during cell division
cycle results in the gain or loss of a chromosome(s),
called aneuploidy
• Turner's syndrome results due to loss of an X
chromosome in human females
• Failure of cytokinesis after telophase stage of cell
division results in an increase in a whole set of
chromosomes in an organism and, this phenomenon is
known as polyploidy.
• The total number of chromosomes in a normal human
cell is 46 (23 pairs).
• Out of these 22 pairs are autosomes and one pair of
chromosomes are sex chromosome.
• Sometimes, though rarely, either an additional copy of
a chromosome may be included in an individual or an
individual may lack one of any one pair of chromosomes.
These situations are known as trisomy or monosomy of a
chromosome
• Down's syndrome, Turner's syndrome, Klinefelter's
syndrome are common examples of chromosomal
disorders.
A) Down's Syndrome…
The cause of this genetic disorder is the presence of an
additional copy of the chromosome number 21 (trisomy
of 21). This disorder was first described by Langdon Down
(1866). The affected individual is short statured with
small round head, furrowed tongue and partially open
mouth. Palm is broad with characteristic palm crease.
Physical, psychomotor and mental development is
retarded.

B) Klinefelter's Syndrome:---
This genetic disorder is also caused due to the presence
of an additional copy of X chromosome resulting into a
karyotype of 47. XXY. Such an individual has overall
masculine development, however, the feminine
development (development of breast, L.e.,
Gynaecomastia) is also expressed.
Such individuals are sterile.

C) Turner's Syndrome:---
Such a disorder is caused due to the absence of one of
the X chromosomes, Le.. 45 with XO, such females are
sterile as ovaries are rudimentary besides other features
including lack of other secondary sexual characters.
 CONCLUSION
In this project, we explored the fundamental principles of
genetics, including inheritance patterns, genetic variation, and
the role of DNA in determining traits. Our investigation
highlighted how genetic material is passed from one generation
to the next through mechanisms like Mendelian inheritance,
and how modern techniques such as CRISPR and genomic
sequencing have expanded our understanding of gene function
and expression.

We also observed the impact of genetic mutations on health

and disease, underscoring the importance of genetic research in
fields like medicine, agriculture, and biotechnology. Overall,
genetics plays a crucial role in shaping both individual traits and
broader population characteristics, offering vast potential for
improving human health and addressing global challenges like
food security.

Further studies and advancements in genetics will continue to

enhance our understanding of complex traits and genetic
diseases, potentially leading to breakthroughs in personalized
medicine, gene therapy, and sustainable agricultural practices.

This conclusion brings together the major points and

emphasizes the significance of genetics in various fields, while
also acknowledging the potential for future discoveries."
BIBLIOGRAPHY

✓ NCERT TEXTBOOK CLASS XII

✓ https://ncert.nic.in

✓ https://byjus.com