G RE G O R
J OH N N N
ME ND E L
M E ND E LI A N
I N H E RI TA N C E
THE
FOUNDATION
OF GENETIC S
ACKNOWLEDGEMENT
I would like to take this opportunity to express special
gratitude to my biology teacher
Ms. Arunima Saxena as well as our principal
Mr. Shekhar Sharma who gave me the wonderful
opportunity to do this project on the topic
“Mendelian Inheritance”.
The opportunity to participate in this project has
helped me improve my research skills and I am really
grateful to them.
I would also like to thank my family and friends for
constantly encouraging me during this project, which
I could not have completed without their support and
continuous encouragement.
INTRODUCTION
GENETICS
–---
GENETICS –
Genetics is the scientific study of genes and
heredity—of how certain qualities or traits are
passed from parents to offspring as a result of
changes in DNA sequence, it forms one of the
central pillars of biology .
GENE-
A gene is a segment of DNA that contains
Instructions for building one or more molecules
that help the body work.
3
TRAITS-
A trait, as related to genetics, is a specific characteristic of an individual. Traits
can be determined by genes, environmental factors or by a combination of
both.
ALLELE-
Genes governing variations of the same characteristic (trait) that occupy corresponding positions
(loci) on homologous chromosomes; alternative forms of a gene.
HOMOZYGOUS –
Possessing a pair of identical alleles for a particular locus (gene).
HETEROGYGOUS-
Possessing a pair of unlike alleles for a particular locus (gene).
FILIAL GENERATION (F)-
The generation that receives gametes from the parental generation.
PARENT GENERATION (P)-
The generation that supplies gametes to the filial generation.
GENOTYPE-
the genetic make-up (the assemblage of alleles) of an individual.
PHENOTYPE-
the physical or chemical expression of an organism’s genes.
CHROMOSOME-
structures within the nucleus of eukaryotic cells composed of chromatin and
visible at cell division (condensed chromatin).
HYBRID-
an offspring resulting from the mating between individuals of two different genetic constitutions.
Families in which all members have
Identical sequence belong to
simple(classical) multi gene family.
rRNA genes is an classic example for
simple multigene family.Human cell
contain about 200rRNA gene copies
haploid chromosome.
This repeated rRNA genes are
needed to meet the great cellular
demand for transcripts.
SIGNIFICANCE OF GENETICS –
-A few of these characteristics are favourable and are called as beneficial
mutations which provide a better survival benefit to changing surroundings .
5
-Evolution of a new class of species altogether occurs when a permanent
change takes place in the phenotype of an entity as a result of natural selection
and competition when an environment continues to stay for longer durations
incorporating better-adapted entities.
- Gene mutations cause the evolution we observe. It causes a change either in
the organization or amount of genetic material in a cell. Such a mutation if
occurred in a gamete can be easily inherited by the emerging gamete
-New alleles of genes are produced as a result of mutations and hence the
variations between entities. Therefore, genes and genetic mutations play a
significant role in the process of evolution.
-Genetics also can help us understand how medical conditions happen.
GREOGOR MENDEL
THE FATHER OF GENETICS
BIOGRAPHY /BACKGROUND-
- Mendel, baptised Johannes, was born on 22 July 1822 at Heinzendorf in
Moravia, then part of Austria, now in the Czech Republic. He was the only
son of struggling peasant farmers who also had two daughters.
- Initially Mendel attended the village school in Heinzendorf. There, the parish
priest, Johann Schreiber, also an expert in fruit growing, recognised his
talents and persuaded his parents to continue his education in spite of their
limited resources.
- At the age of 12 he was sent to the gymnasium in Troppau where he studied
for the next six years
- In 1843 at the age of 21, Mendel entered the Augustinian Order at St
Thomas Monastery near Bru¨nn (now Brno), took the name of Gregor, and
began his theological studies at the Episcopal Seminary there. He was
ordained to the priesthood in 1847.
- Between 1857 and 1864 Mendel undertook a series of hybridisation
experiments in the Monastery’s garden, which were breathtaking for their
brilliance in planning, observation, and analysis, and in interpretation of
results
MENDEL’S EXPERIMENTS-
-Mendel studied inheritance in peas (Pisum
sativum). He chose peas because they had
been used for similar studies, are easy to
grow and can be sown each year. Pea
flowers contain both male and female parts,
called stamen and stigma, and usually self-
pollinate. Self-pollination happens before the
flowers open, so progeny are produced from
a single plant.
-Peas can also be cross-pollinated by hand,
simply by opening the flower buds to remove
their pollen-producing stamen (and prevent
self-pollination) and dusting pollen from one
plant onto the stigma of another. MENDEL’S RESEARCH GARDEN
(AT ST. THOMAS ABBEY)
-Mendel followed the inheritance of 7 traits in pea plants, and each trait had 2
forms. He identified pure-breeding pea plants that consistently showed 1 form
of a trait after generations of self-pollination.
-Mendel then crossed these pure-breeding lines of plants and recorded the
traits of the hybrid progeny. He found that all of the first-generation (F1) hybrids
looked like 1 of the parent plants. For example, all the progeny of a purple and
white flower cross were purple (not pink, as blending would have predicted).
However, when he allowed the hybrid plants to self-pollinate, the hidden traits
would reappear in the second-generation (F2) hybrid plants.
- Mendel described each of the trait variants as dominant or recessiveDominant traits, like
purple flower colour, appeared in the F1 hybrids, whereas recessive traits, like white flower
colour, did not.
-Mendel did thousands of cross-breeding experiments. His key finding was that there were 3
times as many dominant as recessive traits in F2 pea plants (3:1 ratio).
- Mendel also experimented to see what would Inheriting traits in peas
happen if plants with 2 or more pure-bred traits Mendel crossed pure lines of pea
plants. Dominant traits, like purple
were cross-bred. He found that each trait was flower colour, appeared in the first-
generation hybrids (F1), whereas
inherited independently of the other and
recessive traits, like white flower
produced its own 3:1 ratio. This is theprinciple of colour, were masked. However,
recessive traits reappeared in
independent assortment. second-generation (F2) pea plants
in a ratio of 3:1 (dominant to
recessive).
-In 1866, Mendel published the
paper Experiments in plant
hybridisation (Versuche über plflanzenhybriden). In it, he proposed that
heredity is the result of each parent passing along 1 factor for every trait. If the
factor is dominant, it will be expressed in the progeny. If the factor is
recessive, it will not show up but will continue to be passed along to the next
generation. Each factor works independently from the others, and they do not
blend.
-The science community ignored the paper, possibly because it was ahead of
the ideas of heredity and variation accepted at the time. In the early 1900s, 3
plant biologists finally acknowledged Mendel’s work. Unfortunately, Mendel
was not around to receive the recognition as he had died in 1884.
LAWS OF INHERITANCE-
The two experiments lead to the formulation of Mendel’s laws known as laws of
inheritance which are:
1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment
MENDEL’S LAWS
THE LAW OF DOMINANCE-
Mendel’s law of dominance states that:
“When parents with pure, contrasting traits are crossed
together, only one form of trait appears in the next
generation. The hybrid off springs will exhibit only the
dominant trait in the phenotype.”
-Law of dominance is known as the first law of inheritance. In this law, each
character is controlled by distinct units called factors, which occur in pairs. If
the pairs are heterozygous, one will always dominate the other.
-Law of dominance explains that in a monohybrid cross between a pair of
contrasting traits, only one parental character will be expressed in the F1
generation and both parental characters will be expressed in the F2
generation in the ratio 3:1.
-The one which is expressed in the F1 generation is called the dominant trait
and the one which is suppressed is called a recessive trait. In simple words,
the law of dominance states that recessive traits are always dominated or
masked by the dominant trait. This law can be described by Mendel’s
experiment.
-A monohybrid cross is a cross between the two monohybrid traits (TT and tt).
Here plants which have the same characters, but differ in only one character
were crossed.
-For monohybrid cross, Mendel began with a pair of pea plants with two
contrasting traits, i.e., one tall and another dwarf. The cross-pollination of tall
and dwarf plants resulted in tall plants and the offspring were called F1
progeny. The trait which is expressed in the phenotype is called the dominant
trait while the one that is not is called the recessive trait.
-He then continued his experiment with self-pollination of F1 progeny plants.
This resulted in both tall and short plants in the ratio of 3:1 which gave rise to
the law of segregation
THE LAW OF SEGREGATION-
Mendel’s law of segregation states that:
“During the formation of gamete, each gene separates
from each other so that each gamete carries only one
allele for each gene.”
-Law of segregation is the second law of inheritance. This law explains that
the pair of alleles segregate from each other during
meiosis cell division (gamete formation) so that only one allele will be present
in each gamete.
-In a monohybrid cross, both the alleles are expressed in the F2 generation
without any blending. Thus, the law of segregation is based on the fact that
each gamete contains only one allele.
-This law is based on four basic concepts:
A gene exists in more than one form of an allele.
When gametes are produced by meiosis, the allelic pairs separate,
leaving each gamete with a single allele.
Every organism inherits two alleles for each trait.
The two alleles of a pair are different, i.e., one is dominant and one is
recessive.
THE LAW OF INDEPENDENT
ASSORTMENT-
“The law of independent assortment states that the allels
of different genes are inherited independently within the
organisms that reproduce sexually.”
According to the law of independent assortment, the alleles of two more genes
get sorted into gametes independent of each other. The allele received for one
gene does not influence the allele received for another gene.
Mendel’s experiment always portrayed that the combinations of traits of the
progeny are always different from their parental traits. Based on this, he
formulated the Law of Independent Assortment.
Reasons for Independent Assortment
Independent assortment takes place during the process of meiosis. In this
process, the chromosomes are halved and are known as haploid.
To understand the law of independent assortment, it is very important to
understand the law of segregation. In this, two different genes are sorted into
different gamete cells. On the other hand, the law of independent assortment
occurs when the maternal and paternal genes are divided randomly.
Mendel’s Experiment on the Law of Independent Assortment
The Law of Independent Assortment states that during a dihybrid cross
(crossing of two pairs of traits), an assortment of each pair of traits is
independent of the other. In other words, during gamete formation, one pair of
trait segregates from another pair of traits independently. This gives each pair
of characters a chance of expression.
In the dihybrid cross, he chose round-yellow seed and wrinkled green seed and
crossed them. He obtained only round yellow seeds in the F1 generation. Later,
self-pollination of F1 progeny gave four different combinations of seeds in the
F2 generation. He obtained round-yellow, wrinkled-yellow, round green and
wrinkled green seeds in the phenotypic ratio 9:3:3:1.
The phenotypic ratio 3:1 of yellow: green colour and the ratio 3:1 of the round:
wrinkled seed shape during monohybrid cross was retained in the dihybrid
cross as well. Thus, he concluded that characters are distributed independently
and inherited independently. Based on this observation, he developed his third
law – Law of Independent Assortment.
The dihybrid crosses between the parental genotype RRYY (round yellow
seeds) and rryy (green wrinkled seeds) explains the law. Here the chances of
formation of gametes with the gene R and the gene r are 50:50. Also, the
chances of formation of gametes with the gene Y and the gene y are 50:50.
Thus, each gamete should have either R or r and Y or y.
EXCEPTIONS TO MENDELIAN
INHERITANCE-
The three exceptions to Mendel's observations are:
Law of co-dominance, Law of incomplete dominance, and Pleiotropy.
1. Law of Co-dominance:
1. In co-dominance heterozygotes express the phenotype of both parents
e.g. ABO blood groups and sickle cell anemia.
2. In co-dominance, there is an independence of allele function.
3. Neither allele is dominant or partially dominant over the other.
2. Law of incomplete dominance:
1. One allele is not completely dominant to another. F1 is intermediate
between both parents.
2. The phenotype of the heterozygote is intermediate between the
phenotypes of homozygotes for each allele.
3. Example - flower color in the four o'clock plant (Mirabilis jalapa).
3. Pleiotropy:
1. The term pleiotropy is derived from the Greek word “pleio”, which means
“many”, and tropic, which means “affecting”.
2. Genes that affect multiple, apparently unrelated, phenotypes are thus
called pleiotropic genes.
3. Example of pleiotropy in humans in phenylketonuria.
PUNNETT SQAURE AND
GENETIC RATIOS
PUNNETT SQUARE-
-The Punnett square is a square diagram that is used to predict the genotypes
of a particular cross or breeding experiment. It is named after Reginald C.
Punnett, who devised the approach in 1905.
-A diagram that represents the possible genotypes of offspring, developed
after the event of breeding.
-It was first developed by geneticist Reginald Punnette.
-The possible genotypes of offspring are represented in tabular form.
-Each box in the table represents one
event of fertilization
-Each allele in every Punnett square is
represented by the first letter of the
dominant phenotype
MONOHYBRID CROSS-
-“A monohybrid cross is the hybrid of two individuals with homozygous
genotypes which result in the opposite phenotype for a certain genetic trait.”
-“The cross between two monohybrid traits (TT and tt) is called a Monohybrid
Cross.”
-Monohybrid cross is responsible for the inheritance of one gene. It can be
easily shown through a Punnett Square.
-Monohybrid cross is used by geneticists to observe how homozygous
offspring express heterozygous genotypes inherited from their parents.
-He continued his experiment with self-pollination of F1 progeny plants.
Surprisingly, he observed that one out of four plants were dwarf while the
other three were tall. The tall and the short plants were in the ratio of 3:1.
DIHYBRID CROSS-
-A dihybrid cross is a breeding experiment between two organisms which are
identical hybrids for two traits. In other words, a dihybrid cross is a cross
between two organisms, with both being heterozygous for two different traits.
The individuals in this type of trait are homozygous for a specific trait. These
traits are determined by DNA segments called genes.
-In a dihybrid cross, the parents carry different pair of alleles for each trait.
One parent carries homozygous dominant allele, while the other one carries
homozygous recessive allele. The offsprings produced after the crosses in the
F1 generation are all heterozygous for specific traits.
SEX LINKED INHERITANCE
INHERITANCE OF SEX TRAITS-
-Sex-linked genes are located on the X
chromosome result in X-linkage. Similarly, Y-linkage
refers to the gene which is present on the Y
chromosome. Since females are homogametic with
XX chromosome and males have XY chromosome,
the Y-linked traits are transmitted via males only.
-Males are more affected by sex-linked traits in
comparison to females because they are
heterozygous.
-The female passes the X-linked inheritance to both son and daughter, as they
are homozygous to the X chromosome and pass the X chromosome to both
offspring.
MODERN GENETICS
Modern genetics focuses on the chemical substance that genes are made of,
called deoxyribonucleic acid, or DNA, and the ways in which it affects the
chemical reactions that constitute the living processes within the cell.
SELECTIVE BREEDING-
The process by which humans use animal breeding and plant breeding
to selectively develop particular phenotype traits
(characteristics) by choosing which typically
animal or plant males and females will sexually
reproduce and have offspring together is
called selective breeding.
In short, breeding sheep with special characters,
is called selective breeding (also called artificial
selection).
Selective breeding is done to have sheep with
soft hair.
GENETIC ENGINEERING -
Genetic engineering, also called genetic
modification, is the direct manipulation of an
organism’s genome using biotechnology. It
is a set of technologies used to change the
genetic makeup of cells, including the
transfer of genes within and across species
boundaries to produce improved or
novel organisms
DNA SEQUENCING-
DNA sequencing is also a molecular
biology technique that is used to identify
the order of nucleotides in DNA sequence.
This determines the physical order of
nucleobases (A, T, C, G) in a DNA
molecule. This sequencing technique is
basic for scientific research, medical
diagnosis, forensics, etc. It also requires
the use of cloning or PCR techniques to
amplify the given DNA sample.
GENE THERAPHY-
Gene therapy is a technique which
involves the replacement of the
defective genes with healthy ones in
order to treat genetic disorders. It is an
artificial method that introduces DNA
into the cells of the human body. The
first gene therapy was successfully
accomplished in the year 1989.
HUMAN GENETIC DISORDERS-
-Genetic disorders are due to alterations or abnormalities in the genome of an
organism. A genetic disorder may be caused by a mutation in a single gene or
multiple genes. It can also be due to changes in the number or structure of
chromosomes.
-Following is the list of genetic disorders that occur in humans:
1. Cystic fibrosis
2. Thalassemia
3. Huntington’s disease
4. Hemochromatosis
5. Turner’s syndrome
6. Kleinfelter’s syndrome
7. Leber’s Hereditary Optic
Atrophy etc.
ETHICAL AND
SOCIAL IMPLICATIONS -
ETHICAL CONDERATIONS-
-The human genome project is very
useful, but presents difficult political,
social, and cultural issues for society to
deal with. A living organism is one of the
hardest things to study. Its DNA is always
duplicating within its cells and can mutate
at any moment. Knowledge of how these
strands of DNA work is not necessarily a
good thing to know. Some capability of
taking this knowledge and misusing it.
-There are a few ethical dilemmas that
cause people concern. Being able to
actually procure the information that
lies in the DNA's structure could result
in people being discriminated against
for a job or insurance coverage.
Another issue that causes controversy
is the prospect of selection of fetuses
during pregnancy.
GENETIC PRIVACY -
Genetic privacy involves the concept of personal privacy concerning the
storing, repurposing, provision to third parties, and displaying of information
pertaining to one's genetic information. This concept also encompasses privacy
regarding the ability to identify specific individuals by their genetic sequence,
and the potential to gain information on specific characteristics about that
person via portions of their genetic information, such as their propensity for
specific diseases or their immediate or distant ancestry.
CONCLUSION
- Conclusion that Mendel drew from his experiments
is that the traits are inherited in discrete units one
from each parent and are not the result of blending.
He called these discrete units factors which occur
in pairs.
The genes are transferred from parents to the offspring in pairs known as
alleles. During gametogenesis when the chromosomes are halved, there is a
50% chance of one of the two alleles to fuse with the allele of the gamete of the
other parent.
-----------------------------------------------------------------------
I love you
tooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooo
ooooooooooooooooooooooo so fucking
muchhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
31
