Chromosomes and Genes: The Instruction Manual of Life 

Have you ever wondered why you look like your parents or why siblings can look similar but not exactly the same? The answer lies inside your cells—in tiny structures called chromosomes and genes. These two work together to carry instructions that make you who you are.


What Is a Chromosome?

A chromosome is a thread-like structure found in the nucleus of a cell. Chromosomes are made of DNA(deoxyribonucleic acid) and proteins.

Key Facts About Chromosomes

  • Humans have 46 chromosomes in most body cells
  • They are arranged in 23 pairs
  • One chromosome in each pair comes from the mother, and the other comes from the father
  • Chromosomes carry thousands of genes

Chromosomes act like organized folders that store important information needed for growth, development, and daily body functions.


What Is a Gene?

A gene is a small section of DNA found on a chromosome. Each gene carries instructions for making a specific protein, which controls traits and body functions.

Examples of Traits Controlled by Genes

  • Eye color 👀
  • Hair texture 💇
  • Height 📏
  • Blood type 🩸

Genes determine how your body looks and works, but the environment (like diet and exercise) can also influence how some genes are expressed.

How Are Chromosomes and Genes Related?

Think of it this way:

  • Chromosome → a book
  • Gene → a sentence in the book
  • DNA → the letters that make up the sentence

Each chromosome contains many genes, and together they provide all the instructions needed to build and maintain an organism.


Why Are Chromosomes and Genes Important?

Chromosomes and genes are important because they:

  • Pass traits from parents to offspring
  • Control how cells grow and divide
  • Help doctors understand genetic disorders
  • Play a role in inheritance and evolution

Changes or mistakes in genes or chromosomes can sometimes lead to genetic conditions.


Fun Fact! 

Even though all humans have the same number of chromosomes, no two people (except identical twins) have the exact same genes!


Worksheets:


Part 1: Vocabulary Match

Match the term with the correct definition. Write the letter on the line.

  1. _____ Chromosome
  2. _____ Gene
  3. _____ DNA
  4. _____ Trait

Definitions:

A. A characteristic passed from parents to offspring
B. A section of DNA that controls a specific trait
C. A thread-like structure that carries genes
D. The molecule that carries genetic information


Part 2: Multiple Choice

Circle the correct answer.

  1. Where are chromosomes found?
    A. Cytoplasm
    B. Cell membrane
    C. Nucleus
    D. Ribosome
  2. How many chromosomes do humans usually have?
    A. 23
    B. 46
    C. 92
    D. 44
  3. Genes are made of:
    A. Protein
    B. Cells
    C. DNA
    D. Blood
  4. Which trait is controlled by genes?
    A. Shoe size
    B. Eye color
    C. Favorite food
    D. Favorite movie

Part 3: Fill in the Blanks

Use the words below to complete the sentences.

(genes, chromosomes, DNA, parents)

  1. Chromosomes are made of __________.
  2. Genes are found on __________.
  3. Traits are passed down from __________ to offspring.
  4. Each gene carries instructions for making __________.

Part 4: True or False

Write T for true or F for false.

  1. _____ All genes are found inside chromosomes.
  2. _____ Humans get all their chromosomes from one parent.
  3. _____ Genes help determine traits.
  4. _____ DNA carries instructions for life.


Part 5: Short Answer

Answer in 1–2 sentences.

  1. What is the difference between a gene and a chromosome?

.........................................................................................................................................................................................................................................................................................................................................................................................


  1. Why are chromosomes important?Ans:.............................................................................................................................................................................................................................................................................................................................................................Answer Key

    Part 1

    1. C
    2. B
    3. D
    4. A

    Part 2

    1. C
    2. B
    3. C
    4. B

    Part 3

    1. DNA
    2. chromosomes
    3. parents
    4. genes

    Part 4

    1. T
    2. F
    3. T
    4. T

    Part 5 (Sample Answers)

    1. A chromosome is a structure that holds many genes. A gene is a small section of DNA that controls a trait.
    2. Chromosomes carry genetic information and pass traits from parents to offspring.

Topic: The Cell Cycle

Name: _______________________
Date: _______________________
Class: _______________________


Part 1: Vocabulary Match

Match the term with the correct definition. Write the letter on the line.

  1. _____ Cell Cycle
  2. _____ Interphase
  3. _____ Mitosis
  4. _____ Cytokinesis

Definitions:

A. Division of the cytoplasm to form two cells
B. The series of stages a cell goes through as it grows and divides
C. The stage where the cell grows and copies DNA
D. Division of the nucleus


Part 2: Multiple Choice

Circle the correct answer.

  1. Which stage takes the longest time in the cell cycle?
    A. Mitosis
    B. Cytokinesis
    C. Interphase
    D. Prophase
  2. During which stage does DNA replication occur?
    A. G1
    B. S
    C. G2
    D. M
  3. What is the main purpose of mitosis?
    A. Make energy
    B. Repair DNA
    C. Make two identical cells
    D. Move proteins
  4. Cytokinesis happens:
    A. Before mitosis
    B. During interphase
    C. After mitosis
    D. Instead of mitosis


Part 3: Fill in the Blanks

Use the words below.

(interphase, mitosis, cytokinesis, DNA)

  1. __________ is the stage when the cell grows and prepares to divide.
  2. __________ is the division of the nucleus.
  3. __________ carries genetic information.
  4. __________ is when the cytoplasm divides.


Part 4: True or False

Write T for true or F for false.

  1. _____ Interphase includes G1, S, and G2 phases.
  2. _____ Mitosis produces two identical daughter cells.
  3. _____ DNA is copied during mitosis.
  4. _____ Cytokinesis happens at the same time as mitosis.


Part 5: Short Answer

Answer in 1–2 sentences.

  1. Why is the cell cycle important?


  1. What happens during interphase?



Answer Key

Part 1

  1. B
  2. C
  3. D
  4. A

Part 2

  1. C
  2. B
  3. C
  4. C

Part 3

  1. Interphase
  2. Mitosis
  3. DNA
  4. Cytokinesis

Part 4

  1. T
  2. T
  3. F
  4. T

Part 5 (Sample Answers)

  1. The cell cycle is important because it allows organisms to grow, repair damaged cells, and replace old cells.
  2. During interphase, the cell grows, carries out normal functions, and copies its DNA.

Mitosis and Meiosis: How Cells Divide

All living organisms grow, repair themselves, and reproduce using a process called cell division. There are two main types of cell division: mitosis and meiosis. Although they sound similar, they have very different purposes.


What Is Mitosis?

Mitosis is the type of cell division that helps the body grow and repair itself.

Key Facts About Mitosis

  • Occurs in body (somatic) cells
  • Produces two identical daughter cells
  • Each new cell has the same number of chromosomes as the original cell
  • Used for growth, repair, and replacement of cells

Stages of Mitosis

  1. Prophase – Chromosomes become visible
  2. Metaphase – Chromosomes line up in the middle of the cell
  3. Anaphase – Chromatids are pulled apart
  4. Telophase – Two nuclei form

After mitosis, cytokinesis divides the cytoplasm, creating two separate cells.


What Is Meiosis?

Meiosis is a special type of cell division that produces sex cells (sperm and eggs).

Key Facts About Meiosis

  • Occurs in reproductive cells
  • Produces four daughter cells
  • Daughter cells are genetically different
  • Each cell has half the number of chromosomes
  • Important for sexual reproduction

Meiosis happens in two stages: Meiosis I and Meiosis II.

Why Are Mitosis and Meiosis Important?

  • Mitosis helps organisms grow and heal injuries.
  • Meiosis creates genetic diversity, which helps species survive and adapt.

Without these two processes, life as we know it would not be possible.


Fun Fact! 

Human body cells have 46 chromosomes, but human sex cells (sperm and eggs) have 23 chromosomes!


Final Thoughts

Mitosis and meiosis are both essential forms of cell division, but they serve different roles. Mitosis keeps your body healthy, while meiosis makes reproduction possible and ensures genetic variation.

Chromatids are identical copies of a chromosome that are formed during cell division.


When a cell gets ready to divide, it copies its DNA. 

After this copying:

  • Each chromosome is made of two identical halves
  • These halves are called sister chromatids
  • The sister chromatids are joined together at a point called the centromere


Key Points About Chromatids

  • Chromatids form before cell division
  • Each chromatid has the same DNA information
  • During mitosis and meiosis, sister chromatids separate
  • Once they separate, each chromatid becomes a new chromosome


Easy Way to Remember 

Think of a chromosome like a zipper:

  • Before copying → one side
  • After copying → two identical sides (chromatids)
  • When they separate → each side becomes its own chromosome


One-Sentence Definition

👉 A chromatid is one of two identical copies of a chromosome that are attached at the centromere. 

Worksheets

Chromosomes and Genes – The Instruction Manual of Life

Every living organism has a set of instructions that tells its body how to grow, develop, and function. These instructions are written in a chemical called DNA (Deoxyribonucleic Acid). DNA is organized into structures called chromosomes, which are found in the nucleus of most cells. Humans have 46 chromosomes, arranged in 23 pairs.

Each chromosome contains many genes, which are segments of DNA that provide specific instructions for making proteins. Proteins carry out essential functions in the body, such as building tissues, transporting substances, and supporting chemical reactions.

Genes determine traits such as eye color, blood type, and even some aspects of behavior. Some traits are inherited from parents, while others can be influenced by the environment. Chromosomes and genes together act like an instruction manual for life, guiding the development and functioning of every living thing.


Comprehension Questions

1. What is DNA, and where is it found in a cell?

................................................................................................................................

2. What are chromosomes, and how many do humans have?

...............................................................................................................................

3. Define a gene.

..............................................................................................................................

4. What role do proteins play in the body?

..............................................................................................................................

5. Give two examples of traits determined by genes.

.............................................................................................................................

6. How do chromosomes and genes act like an “instruction manual”?

............................................................................................................................

7. Can traits be influenced by factors other than genes? Explain.

.............................................................................................................................

8. Why do humans have chromosomes in pairs?

............................................................................................................................



  1. Answer: DNA is a chemical that carries the instructions for growth, development, and function of an organism. It is found in the nucleus of most cells.
  2. Answer: Chromosomes are structures that organize DNA. Humans have 46 chromosomes, arranged in 23 pairs.
  3. Answer: A gene is a segment of DNA that provides instructions for making proteins.
  4. Answer: Proteins carry out essential functions, such as building tissues, transporting substances, and supporting chemical reactions.
  5. Answer: Eye color and blood type.
  6. Answer: They provide the instructions needed for the development, growth, and functioning of an organism.
  7. Answer: Yes, some traits can be influenced by environmental factors, such as diet, exercise, and lifestyle.
  8. Answer: Humans have chromosomes in pairs because we inherit one chromosome of each pair from each parent, ensuring genetic variation and proper function.

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