Name -S.
Kishore
Class- 10‘A’
Roll No.- 1003
Subject- Science [Biology]
Submitted to- Sinduja Mam
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Acknowledgement
I would like to express my special
thanks of gratitude to my teacher Mrs.
Sinduja Mam as well as our principal sir
Mr. T.Pravinkumar who gave me the
golden opportunity to do this wonderful
project on the topic “Hereditary”, which
also helped me in doing a lot of research.
I came to know about much new things.
I am really thankful to them, also I
would also like to thank my elder
brother who helped me a lot in finalizing
this project within the limited time
frame.
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Certificate
This is to certify that S.Kishore of class 10th
‘A’ is awarded this certificate for
completion of the project on ‘Consumer
Rights’ under the guidance of Mrs. Sinduja
Mam.
Teacher’s Signature ________________
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Index
1. Introduction to Heredity
2. Important Terminologies in Heredity
4. Mendel’s Laws of Inheritance
3. Gregor Mendel and His Experiments
5. Monohybrid Cross
6. Dihybrid Cross
7. Inherited Traits vs Acquired Traits
8. DNA, Genes, and Chromosomes
9. Genetic Disorders
10. Applications of Heredity
11. Evolution and Heredity
12. Additional Concepts
13. Importance of Variations
14. Conclusion
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1. Introduction to
Heredity
Definition:
Heredity is the biological process through which parents pass on their genetic
information, traits, and characteristics to their offspring. This process ensures
the continuity of species by transferring physical, biochemical, and sometimes
behavioral traits from one generation to another.
Why is Heredity Important?
It explains family resemblances and variations among individuals.
It is the foundation of genetics, the branch of biology that studies
inheritance.
Heredity affects health, behavior, and appearance of living beings.
Detailed Explanation:
Every organism’s body is made up of cells. Inside each cell’s nucleus are
structures called chromosomes, which carry genes—units of heredity. Genes are
made of DNA and determine specific traits by coding for proteins. These
proteins control physical features and biological processes. When organisms
reproduce, they pass copies of their genes to their offspring, which leads to
inherited traits.
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2. Important
Terminologies in
Heredity
Term Explanation
Gene A section of DNA responsible for a specific trait.
Long DNA molecules bundled into thread-like structures in the nucleus. Humans
Chromosome
have 46 chromosomes (23 pairs).
Allele Different forms of the same gene, e.g., allele for tallness (T) and dwarfness (t).
Genotype The genetic makeup of an organism, e.g., TT, Tt, or tt.
Phenotype Observable characteristics or traits, e.g., tall or dwarf.
Dominant An allele that expresses itself even if only one copy is present.
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Term Explanation
Allele
Recessive Allele An allele that is masked by the dominant allele unless present in two copies.
Homozygous When both alleles for a trait are the same (TT or tt).
Heterozygous When the two alleles for a trait are different (Tt).
Hybrid An organism resulting from the cross of two different types (heterozygous for a trait).
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3. Gregor Mendel and
His Experiments
Background:
Gregor Johann Mendel was an Austrian monk who lived in the 19th century and
is known as the Father of Genetics. His experiments on pea plants revealed how
traits are inherited.
Why Pea Plants?
They have easily distinguishable traits with contrasting characteristics.
They grow quickly and produce many offspring.
They can be artificially cross-pollinated or self-pollinated.
Traits Mendel Studied:
Height: Tall (T) vs. Dwarf (t)
Seed Shape: Round (R) vs. Wrinkled (r)
Seed Color: Yellow (Y) vs. Green (y)
Flower Color: Purple (P) vs. White (p)
Pod Shape: Inflated vs. Constricted
Pod Color: Green vs. Yellow
Flower Position: Axial vs. Terminal
Mendel’s Experimental Method:
Mendel selected pure breeding plants (homozygous for traits).
He cross-pollinated contrasting traits (e.g., tall × dwarf).
Observed the first generation (F1) traits.
Allowed F1 to self-pollinate to produce F2 generation and recorded trait
ratios.
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4. Mendel’s Laws of
Inheritance
4.1 Law of Dominance
When two different alleles are present in an organism, one allele
dominates and masks the expression of the other.
For example, tallness (T) is dominant over dwarfness (t), so Tt plants
appear tall.
4.2 Law of Segregation
During gamete formation, the two alleles for a trait separate so that each
gamete receives only one allele.
Upon fertilization, the offspring receives one allele from each parent.
4.3 Law of Independent Assortment
Alleles of different genes segregate independently of one another during
gamete formation, provided they are on different chromosomes.
This law explains the inheritance of multiple traits simultaneously.
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5. Monohybrid Cross
Definition:
A genetic cross focusing on a single trait.
Example:
Cross between pure tall (TT) and dwarf (tt) pea plants.
All F1 offspring (Tt) are tall, showing dominance of the tall trait.
When F1 plants self-pollinate:
Genotype Phenotype Number of Plants (F2)
TT Tall 1
Tt Tall 2
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Genotype Phenotype Number of Plants (F2)
tt Dwarf 1
Phenotypic Ratio: 3 tall : 1 dwarf
Genotypic Ratio: 1 TT : 2 Tt : 1 tt
Importance:
Monohybrid crosses helped Mendel discover dominant and recessive traits.
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6. Dihybrid Cross
Definition:
A cross that examines the inheritance of two traits simultaneously.
Mendel’s Dihybrid Experiment:
Crossed plants with round yellow seeds (RRYY) with plants having
wrinkled green seeds (rryy).
F1 generation: All round yellow seeds (RrYy).
F1 plants were self-crossed to produce F2.
F2 Phenotypic Ratio:
Phenotype Ratio Description
Round Yellow 9 Both dominant traits
Round Green 3 Dominant round, recessive green
Wrinkled Yellow 3 Recessive wrinkled, dominant yellow
Wrinkled Green 1 Both recessive traits
The 9:3:3:1 ratio supported the Law of Independent Assortment.
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7. Inherited Traits vs
Acquired Traits
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Trait Type Description Examples
Inherited Traits Traits passed genetically from parents Eye color, blood group, freckles
Acquired Traits Traits developed during lifetime, non-genetic Scars, learned skills, language
Note: Acquired traits do not influence genetic material and cannot be passed
on.
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8. DNA, Genes, and
Chromosomes
8.1 What is DNA?
DNA stands for Deoxyribonucleic Acid. It is a long molecule shaped like a
twisted ladder, called a double helix. DNA contains the instructions that
control the growth, development, and functioning of all living organisms.
Structure: DNA is made of four chemical bases: Adenine (A), Thymine
(T), Cytosine (C), and Guanine (G).
The bases pair specifically (A with T, C with G), forming the "rungs" of the
ladder.
The sequence of these bases encodes genetic information.
8.2 What is a Gene?
A gene is a specific segment of DNA that contains instructions to make a
particular protein or to control a specific trait. Genes act as biological blueprints
for building and maintaining an organism.
Each gene has a particular position called a locus on a chromosome.
Different versions of the same gene are called alleles (for example, the
gene for seed color can have a yellow or green allele).
8.3 What are Chromosomes?
Chromosomes are thread-like structures located inside the nucleus of cells.
They are made of tightly coiled DNA and proteins called histones.
Humans have 46 chromosomes, arranged in 23 pairs.
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One chromosome of each pair is inherited from the mother, the other
from the father.
Chromosomes carry thousands of genes.
8.4 How DNA, Genes, and Chromosomes Work Together
DNA molecules coil up to form chromosomes during cell division.
Genes on chromosomes direct the production of proteins through a
process called protein synthesis.
Proteins carry out vital functions and determine traits such as eye color,
height, and blood group.
8.5 DNA Replication and Cell Division
Before a cell divides, it must copy its DNA so each new cell has a complete set
of genes. This process is called DNA replication.
DNA unwinds, and each strand serves as a template for a new
complementary strand.
This ensures that genetic information is accurately passed from cell to
cell, and from parent to offspring.
8.6 Role in Heredity
During reproduction, chromosomes are passed from parents to offspring
through gametes (sperm and egg cells).
The unique combination of genes from both parents results in genetic
variation among offspring.
Additional Points
Feature Description
DNA Location Nucleus (mostly), also mitochondria
Length of DNA About 2 meters per human cell when stretched
Number of Genes Approximately 20,000–25,000 in humans
Gene Expression Genes can be turned “on” or “off” depending on needs
Real-World Examples
Genetic Testing: Uses knowledge of DNA to detect inherited disorders.
Forensic Science: DNA profiling helps in criminal investigations.
Genetic Engineering: Manipulating DNA to improve crops and treat
diseases.
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9. Genetic Disorders
Caused by mutations or inheritance of defective genes.
Examples include:
o Sickle Cell Anemia (defect in hemoglobin gene)
o Cystic Fibrosis (affects lungs and digestion)
o Hemophilia (blood clotting disorder)
Genetic counseling helps families understand risks and inheritance
patterns.
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10. Applications of
Heredity
Agriculture: Development of pest-resistant and high-yield crops.
Medicine: Gene therapy and prenatal genetic diagnosis.
Forensics: DNA fingerprinting for crime solving.
Animal Breeding: Enhancing livestock quality.
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11. Evolution and
Heredity
Genetic variation through heredity is raw material for evolution.
Mutations and recombination introduce new alleles.
Natural selection acts on genetic variation to adapt populations.
Heredity allows beneficial traits to be passed down.
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12. Additional Concepts
12.1 Mutation
Changes in the DNA sequence can lead to new traits or genetic disorders.
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12.2 Multiple Alleles
Some traits are controlled by more than two alleles (e.g., blood groups A, B, AB,
O).
12.3 Sex-linked Traits
Traits associated with genes located on sex chromosomes, such as color
blindness and hemophilia.
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13. Importance of
Variations
What Are Variations?
Variations refer to the differences in physical traits or characteristics among
individuals of the same species. These differences can be slight or significant
and are crucial for the survival and evolution of species.
Types of Variations
1. Genetic Variations:
These arise due to differences in the DNA sequence among individuals.
Genetic variations occur because of:
o Mutation: A change in the DNA sequence which can create new
alleles.
o Recombination: During sexual reproduction, chromosomes
exchange segments, creating new allele combinations.
o Independent Assortment: Random distribution of chromosomes
during gamete formation leads to new gene combinations.
2. Environmental Variations:
These are changes in traits caused by environmental factors such as
climate, food availability, lifestyle, and experiences.
Example: A person’s muscle strength can increase with exercise but this
acquired trait is not inherited.
Why Are Variations Important?
Adaptation: Variations allow species to adapt to changing environments.
For example, some plants may be more drought-resistant than others.
Survival: When conditions change, individuals with beneficial variations
are more likely to survive and reproduce.
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Evolution: Variations provide the raw material on which natural selection
acts, driving evolution.
Biodiversity: Variations increase the diversity within a population, which
helps maintain ecosystem stability and resilience.
Selective Breeding: Humans use variations to breed plants and animals
with desirable traits, improving food crops and livestock.
Example of Variation in Humans
Height, eye color, and blood groups are all examples of inherited
variations.
Skin tanning is an example of environmental variation.
Summary:
Aspect Description
Genetic Variation Differences due to DNA, inherited by offspring.
Environmental Variation Differences caused by surroundings, not inherited.
Role in Evolution Essential for natural selection and adaptation.
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14. Conclusion
Heredity is a fundamental biological process that explains how traits and
characteristics are passed from parents to their offspring through genes. The
pioneering work of Gregor Mendel laid the foundation for modern genetics by
uncovering the principles of inheritance, such as dominance, segregation, and
independent assortment. Understanding heredity helps us explain the variation
seen within species and the patterns by which traits are inherited. Variations,
both genetic and environmental, play a crucial role in the survival and evolution
of organisms, allowing them to adapt to changing environments. Moreover, the
study of heredity has practical applications in medicine, agriculture, and
forensic science, improving our quality of life. Overall, heredity is essential not
only for the continuation of life but also for the diversity and adaptability of
living organisms on Earth.
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Bibliography
(1) NCERT CLASS 10 SCIENCE BOOK
(2) WIKIPEDIA
(3) https://teach.genetics.utah.edu/
(4) https://www.ncbi.nlm.nih.gov/
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(5) https://www.sciencedirect.com/
(6) https://www.britannica.com/science/heredity-
genetics
(7) https://www.livescience.com/27332-
genetics.html
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