Like Father, Like Daughter: CBSE Class 5 EVS Chapter 21

Understanding Inherited vs. Acquired Traits

Every human being is unique, yet we carry distinct signatures of our family members. Physical characteristics passed down from parents to their children through biological processes are called inherited traits. Examples include your eye color, hair texture, skin tone, height, and even the shape of your earlobes. On the other hand, we develop several characteristics after birth based on our environment, training, and lifestyle. These are known as acquired traits. For instance, learning how to speak a specific language, playing musical instruments like the violin, riding a bicycle, or acquiring a scar from a playground fall are all acquired traits. They cannot be biologically passed down to your future children because they do not alter your genetic structure. Understanding this difference helps us appreciate how nature and nurture work together to make us who we are.

How Gregor Mendel Unlocked the Secret of Inheritance

1. Choosing the Pea Plant (Pisum sativum) — Gregor Mendel, an Austrian monk born in 1822, observed that pea plants have distinct, contrasting characteristics (such as tall vs. short height, and yellow vs. green seeds) that make them perfect for studying heredity.
2. First Generation Crossings — He carefully cross-pollinated a pure tall pea plant with a pure short pea plant. He discovered that the first generation of offspring consisted entirely of tall plants. The short trait seemed to completely disappear.
3. Self-Pollinating the Offspring — Next, he allowed these new tall offspring to self-pollinate naturally to see if the short characteristic would return in the second generation.
4. Discovering the Mathematical Ratio — To his surprise, the short trait reappeared! In the second generation, roughly 75% of the plants grew tall, while 25% grew short. This showed that traits are passed down in distinct units (now called genes) that do not simply mix or disappear.

Crucial Facts: Diseases and Genes

• Polio is NOT hereditary: Some diseases, like polio, are caused by external viral infections and are not inherited. A child born to a parent who had polio will NOT automatically have polio.
• Twin Differences: Identical twins share identical genes and look very similar, whereas fraternal twins develop from separate eggs and look different, sometimes even having different genders.
• Acquired Physical Changes: Physical changes resulting from accidents, diseases, or surgeries are not passed on to offspring because they are not coded in our DNA.
• Environmental Impact: Good health, access to clean drinking water, and nutritious food are critical for a child's growth, regardless of their inherited genetic traits.

Practice Questions with Solutions

• Q: What is the main difference between inherited traits and acquired traits? Provide examples. A: Step 1: Define inherited traits as physical characteristics passed from parents to offspring biologically. Example: Curly hair or brown eyes. Step 2: Define acquired traits as skills or habits learned through practice or environmental exposure. Example: Knowing how to swim or speak Hindi. Final answer: Inherited traits are present from birth via genes (e.g., eye color), while acquired traits are developed during a lifetime through experiences (e.g., playing piano).
• Q: Is polio a hereditary disease? Explain your answer. A: Step 1: Define the cause of polio. Polio is caused by a virus (poliovirus) that enters the body through contaminated water or food. Step 2: Address the genetic aspect. Because it is an infectious viral disease, it does not change or affect human genetic DNA. Step 3: State the conclusion. A child of a parent affected by polio will not inherit the disease at birth. Final answer: No, polio is not hereditary. It is an infectious disease caused by a virus, meaning a child of a polio survivor will not be born with polio.
• Q: Who was Gregor Mendel, and what did he discover about traits? A: Step 1: Introduce Mendel. Gregor Mendel was an Austrian monk who conducted experiments on pea plants in his monastery garden. Step 2: Explain his discovery. He discovered that biological traits do not simply blend together. Instead, they are inherited in specific, predictable patterns. Step 3: State the pea plant findings. He showed that crossing tall and short plants produces tall plants, but the short trait can reappear in later generations. Final answer: Gregor Mendel is known as the 'Father of Genetics' for discovering the fundamental laws of trait inheritance using pea plants.
• Q: Why do identical twins look so similar while fraternal twins may look different? A: Step 1: Explain the biological origin of identical twins. They form from a single fertilized egg that splits, meaning they share 100% of the same genetic material. Step 2: Explain fraternal twins. They form from two separate eggs fertilized by two different sperm, sharing only about 50% of their genes. Step 3: Conclude why their appearances differ. High genetic similarity causes identical twins to look almost identical, while low genetic similarity makes fraternal twins look like regular siblings. Final answer: Identical twins share identical DNA, causing them to look highly similar, whereas fraternal twins are genetically distinct and can look completely different.

Frequently Asked Questions