How are genes passed from parents to children?

In one line

The rule

Genes are units of heredity that are passed from parents to offspring through reproductive cells (sperm and egg), determining the traits of the next generation.

Let's understand it simply

Imagine you are making a roti. You use flour from a bag your parents bought. The flour is like the genes—it comes from your parents, and you use it to make something new. In the same way, your body is made from instructions (genes) you got from your parents.

Each parent gives you half of your genes. Your mother gives you half through her egg cell, and your father gives you half through his sperm cell. When these two cells join, they mix their genes, and you get a new set—half from each parent. This is why you may look like your mother, but have your father's smile.

How it works

1. Parents have genes: Each parent has two copies of each gene (one from their mother, one from their father).
2. Formation of gametes: In the mother, eggs are made; in the father, sperm is made. Each egg or sperm gets only one copy of each gene.
3. Fertilisation: When a sperm meets an egg, they join to form a single cell (zygote) with two copies of each gene—one from each parent.
4. Development: The zygote divides and grows, using these genes as instructions to build the body.
5. Traits appear: The combination of genes decides your traits—like skin colour, blood group, or whether you can roll your tongue.
6. Variation: Because the mix is random, siblings (brothers and sisters) can look different, even with the same parents.

The story behind it

The idea that genes are passed from parents to children started with Gregor Mendel, a monk in Austria in the 1800s. He grew pea plants and noticed patterns in how traits like flower colour and seed shape were inherited. Mendel's careful experiments showed that traits are controlled by 'factors' (now called genes) that are passed down in predictable ways. His work was not famous during his life, but later scientists realised how important it was.

Where you see it in real life

• Family resemblances: You may have your father's nose or your mother's hair. These features come from genes passed down.
• Inherited diseases: Some diseases, like sickle cell anaemia or thalassemia, run in families because of genes.
• Blood groups: Your blood group (A, B, AB, O) is decided by genes from your parents.
• Plant breeding: Farmers select seeds from the best plants to get good crops. The traits are passed through genes.
• Animal breeding: Buffaloes or cows are bred for more milk by choosing parents with good genes.
• Twins: Identical twins have the same genes, so they look very similar. Non-identical twins are like normal siblings, with different mixes of genes.

Why it matters

• Understanding heredity: Knowing how genes are passed helps us predict traits in children.
• Medical care: Doctors can check for genetic diseases and advise families.
• Agriculture: Helps in breeding better crops and animals.
• Forensics: DNA from genes is used to identify people in crime cases.

Worked example

Let's say:

• Mother has gene pair for eye colour: BB (brown)
• Father has gene pair: Bb (brown, but carries blue)

Step 1: List possible genes from mother: B
Step 2: List possible genes from father: B or b
Step 3: Make combinations: BB (brown), Bb (brown)
Step 4: All children will have brown eyes, but some can carry the blue gene (b)

Common mistakes

• Thinking you get all traits only from one parent. In reality, you get half your genes from each.
• Believing siblings should look exactly alike. Each child gets a different mix of genes.
• Confusing genes with traits. Genes are instructions; traits are the result.
• Assuming only physical traits are inherited. Many health conditions and even some behaviours have genetic parts.

Remember it

You are a mix of your parents' genes—half from your mother, half from your father, combined in a unique way.