About Gregor Mendel's Theory and its application in Science and Health for Grade9 students who are studying Science 9

1. HEREDITY

2. OBJECTIVES
• The learner should demonstrate
how genetic information genes on
chromosomes.
• Identify the different pattern of
inheritance.

3. Heredity or Hereditary is the process of passing the
traits and characteristics from parents to offsprings
through genes. The offspring, get their features and
characteristics that is genetic information from their
mother and father. Heredity and genetics are the
reason you look so much like your parents. Genetics is
a branch of science that studies the DNA, genes,
genetic variation, and heredity in living organisms. Let
us learn all about it.

4. GREGOR JOHANN MENDEL
Gregor Mendel- The Father of Genetics
Acquiring characteristics or traits from
one generation to the other is nothing
but inheritance. Here, both parents
contribute equally to the inheritance of
traits. Gregor Mendel, also known as
the Father of Genetics, conducted
immense research and studies on this
inheritance of traits.
He researched on plant breeding and
hybridization and conducted his
experiments on pea plants to show the
inheritance of traits in living organisms.

5. KNOW SOME TERMS
Gene – It is the basic unit of inheritance. It consists of a sequence
of DNA, which is the genetic material. Genes can mutate and can
take two or more alternative forms.
Alleles – The alternative forms of genes. They affect the same
characteristics or traits in alternate forms. They are located on the
same place of the chromosome.
Chromosomes – These are thread-like structures made up of
nucleic acids (DNA) and proteins. They are mostly found in the
nucleus of the cells. They carry the hereditary or genetic
in the form of genes.
Genotype – It is the complete heritable genetic identity of an
organism. It is the set of alleles that are carried by the organism. It
also includes non-expressed alleles.
Phenotype – It is the description of the actual physical
characteristics of an organism or the expressed form of the
genotype.

6. Dominant alleles – When an allele affects the phenotype of
an organism, then it is a dominant allele. Capital letters
represent dominant alleles. For example, “T” to express
tallness.
Recessive alleles – An allele that affects the genotype in the
absence of the dominant allele is called a recessive allele.
Small letters represent recessive alleles. For example – “t” for
tallness.
Homozygous – Each organism has two alleles for every
gene (Each chromosome has one each). In homozygous,
both the alleles are same. For Example, “TT” is the
homozygous expression for tallness trait.
Heterozygous – If the two alleles are different from each
other, then they are heterozygous in nature. For Example,
“Tt” is the heterozygous expression for tallness trait.

7. MENDEL’S EXPERIMENT
Monohybrid Cross
It is the cross between
two plants which have
one pair of contrasting
characters. For Example,
cross between a tall pea
plant and a short (dwarf)
plant. The following
diagram explains this in
detail

8. OBSERVATIONS & CONCLUSION
• In Tt, ‘T’ is expressed and ‘t’ is suppressed. Hence, the
characters ‘T’ is the dominant trait and ‘t’ is the
recessive trait.

9. Dihybrid Cross
It is the cross between two
plants which have two pairs of
contrasting characters. This
takes into consideration
alternative traits of two
different characters. For
example, a cross between one
pea plant with round and
green seeds and the other
plant having wrinkled and
yellow seeds. The following
diagram explains the dihybrid
cross in detail.

10. OBSERVATIONS & CONCLUSION
• This shows that the genes
independently inherited.

11. INCOMPLETE DOMINANCE
Mendel’s results were
groundbreaking partly
because they contradicted
the (then-popular) idea that
parents' traits were
permanently blended in
their offspring. In some
cases, however, the
phenotype of a
heterozygous organism can
actually be a blend between
the phenotypes of its

13. CODOMINANCE
Co-Dominance
Both alleles can be
expressed
For example, red cows
crossed with white will
generate roan cows.
Roan refers to cows that
have red coats with
white blotches.

14. MULTIPLE ALLELES
Three or more alternative
forms of a gene (alleles)
that can occupy the same
locus. However, only two
of the alleles can be
present in a single
organism. For example, the
ABO system of blood
groups is controlled by
three alleles, only two of
which are present in an
individual

15. DISEASES

16. • Genetic disorders can be the result of genetic
abnormalities such as gene mutation or
additional chromosomes. The effects of
abnormalities in an individual’s DNA were once
entirely unpredictable. However, modern
medicine has produced methods of identifying
the potential health outcomes of genetic
disorders, as evidenced by medical research
from educated, advanced-degreed nurse
practitioners and practicing physicians. By
collecting the following evidence-based
statistical observations, these professionals
have identified some of the current best
practices for detecting, treating, and potentially
preventing some genetic disorders.

17. DOWN SYNDROME
Typically, the nucleus of an individual cell
contains 23 pairs of chromosomes, but Down
syndrome occurs when the 21st chromosome
is copied an extra time in all or some cells.
Nurse practitioners and physicians commonly
perform detailed prenatal screening tests, like
blood tests, that detect quantities of
chromosomal material and other substances
in a mother’s blood. This type of testing can
determine, with high accuracy, whether or not
a child will be born with Down syndrome.
When a person is diagnosed with Down
syndrome, they are likely to exhibit varying
levels of mild to severe cognitive delays.

18. THALASSEMIA
Thalassemia is a family of
hereditary genetic conditions
that limits the amount of
hemoglobin an individual can
naturally produce. This
condition inhibits oxygen flow
throughout the body. There is
a 25 percent chance that
children who inherit the
Thalassemia gene from both
parents will be born with

19. CRI DU CHAT SYNDROME
A genetic condition present from birth that
affects growth and development. Infants with this
condition often have a high-pitched cat-like cry,
small head size, and a characteristic facial
appearance.
They may have trouble breathing and feeding
difficulties. People with this condition typically
have intellectual disability, developmental and
speech delay, and behavioral issues.
Cri du chat syndrome is due to a missing piece
(deletion) of a specific part of chromosome 5
known as the 'p' arm. In general, the severity of
the symptoms is determined by the size and

20. CYSTIC FIBROSIS
Cystic Fibrosis is a chronic, genetic
condition that causes patients to
produce thick and sticky mucus,
inhibiting their respiratory, digestive,
and reproductive systems. Like
Thalassemia, the disease is commonly
inherited at a 25 percent rate when
both parents have the Cystic Fibrosis
gene. In the United States, there are
close to 30,000 people living with
Cystic Fibrosis, and they frequently
develop greater health problems.

21. TAY-SACHS DISEASE
The genetic condition known as Tay-
Sachs is carried by about one in
every 27 Jewish people, and by
approximately one of every 250
members of the general population.
The condition is caused by a
chromosomal defect similar to that
of Down syndrome. Unlike Down
syndrome, however, Tay-Sachs
results from a defect found in
chromosome #15, and the disorder
is irreversibly fatal when found in

22. SICKLE CELL ANEMIA
Sickle Cell Disease is a lifelong genetic
condition that may be inherited when
the Sickle Cell trait is passed down by
both parents to their children. The trait
is more commonly inherited by people
with a sub-Saharan, Indian, or
Mediterranean heritage. Sickle Cell
Disease causes red blood cells to
change from their usual donut shape to
a sickle shape. This causes the cells to
clump together and become caught in
blood vessels, triggering severe pain
and serious complications such as
infections, organ damage, and acute