Hey, Class 10 students! Welcome to your ultimate guide for Chapter 9: Heredity from the NCERT Science book (2023-24 syllabus). This chapter is all about why you look like your parents—or why you don’t! It’s about how traits pass from one generation to the next, and it’s a big deal for your exams. We’ll break down the main questions with clear, easy answers to help you ace your studies. Let’s dive into the fascinating world of heredity!
What Is Heredity?
Heredity is the process of passing traits—like eye color, height, or even dimples—from parents to kids through genes. It’s why families look alike but also why everyone’s a little unique. This chapter explores how it works in plants, animals, and us humans. Let’s get to the questions!
Key Questions and Answers from Chapter 9
Here are the top questions from Heredity with simple, student-friendly explanations:
Q1: What is heredity? Why is it important?
Answer:
Heredity is how traits are handed down from parents to offspring via genes.
- Why Important: It keeps species going, passes useful traits (e.g., strong roots in plants), and explains why you’re you!
Example: Your curly hair might come from your mom.
Q2: What are genes? Where are they found?
Answer:
- Genes: Tiny units of DNA that carry instructions for traits (e.g., hair color).
- Where: Inside chromosomes, which are in the nucleus of every cell.
Think: Genes are like recipe cards for your body!
Q3: What is the role of chromosomes in heredity?
Answer:
Chromosomes are thread-like structures that hold genes.
- Humans have 46 (23 pairs)—half from mom, half from dad.
- During reproduction, sperm (23) and egg (23) combine to make 46 in the baby.
Fact: One pair (sex chromosomes: XX or XY) decides if you’re a girl or boy!
Q4: What did Mendel discover about heredity?
Answer:
Gregor Mendel, the “father of genetics,” used pea plants to find:
- Traits come in pairs (e.g., tall or short).
- One trait can hide another (dominant vs. recessive).
- Traits pass independently (Law of Segregation, Law of Independent Assortment).
Cool Part: He figured this out in the 1860s with no fancy tech!
Q5: What are dominant and recessive traits?
Answer:
- Dominant: A trait that shows up if present (e.g., tallness in peas, T).
- Recessive: A trait that hides unless both genes are recessive (e.g., shortness, t).
Example: If mom gives T (tall) and dad gives t (short), you’re tall (Tt)—T wins!
Q6: What is a monohybrid cross? Explain with an example.
Answer:
A monohybrid cross studies one trait.
Example: Mendel crossed tall (TT) and short (tt) pea plants:
- F1 Generation: All tall (Tt)—tall is dominant.
- F2 Generation: Self-cross Tt × Tt → 3 tall (TT, Tt, Tt), 1 short (tt).
- Ratio: 3:1.
Think: T masks t in F1, but t shows up in F2!
Q7: What is a dihybrid cross? Give an example.
Answer:
A dihybrid cross studies two traits.
Example: Mendel crossed round-yellow (RRYY) and wrinkled-green (rryy) peas:
- F1: All round-yellow (RrYy).
- F2: 9 round-yellow, 3 round-green, 3 wrinkled-yellow, 1 wrinkled-green.
- Ratio: 9:3:3:1.
Key: Traits mix independently—round doesn’t stick to yellow!
Q8: What are alleles? How do they affect traits?
Answer:
- Alleles: Different forms of a gene (e.g., T for tall, t for short).
- Effect: You get one allele from each parent. If they’re different (Tt), the dominant one shows; if same (tt), that trait appears.
Example: Brown eyes (B) over blue (b)—Bb = brown.
Q9: What is genotype and phenotype?
Answer:
- Genotype: The gene combo (e.g., TT, Tt, tt).
- Phenotype: What you see (e.g., tall or short).
Example: Tt genotype = tall phenotype (T dominates).
Tip: Geno = genes, Pheno = physical!
Q10: How does sexual reproduction cause variation?
Answer:
Sexual reproduction mixes genes from two parents:
- Sperm and egg combine randomly.
- Each parent gives half the chromosomes.
Result: Offspring are unique (e.g., you’re not identical to your siblings).
Why Cool?: Variation helps species adapt!
Q11: What is the Law of Segregation?
Answer:
Mendel’s Law of Segregation says:
- Each parent gives one allele per trait.
- Alleles separate during gamete formation (sperm/egg).
Example: Tt splits into T and t gametes—F2 shows both tall and short.
Q12: What is the Law of Independent Assortment?
Answer:
Mendel’s Law of Independent Assortment says:
- Different traits are inherited separately.
- One trait (e.g., height) doesn’t affect another (e.g., seed color).
Example: Dihybrid cross gives 9:3:3:1—not all round seeds are yellow!
Q13: How is sex determined in humans?
Answer:
Sex depends on the 23rd chromosome pair:
- Females: XX (mom gives X, dad gives X).
- Males: XY (mom gives X, dad gives Y).
- Dad’s sperm decides—X = girl, Y = boy.
Fact: 50-50 chance each time!
Q14: Why don’t offspring look exactly like parents?
Answer:
- Sexual reproduction shuffles genes.
- Mutations (random changes) add differences.
- Dominant/recessive combos vary (e.g., Tt vs. TT).
Example: You might get dad’s nose but mom’s height!
Q15: What is the significance of variation?
Answer:
Variation:
- Helps species survive changes (e.g., disease resistance).
- Makes each individual unique.
- Drives evolution over time.
Think: Variety is nature’s strength!
Extra Questions from NCERT Exercises
- Why did Mendel choose pea plants?
Answer: Easy to grow, quick generations, clear traits (e.g., tall/short). - What is a Punnett square?
Answer: A grid to predict offspring traits (e.g., Tt × Tt = 25% TT, 50% Tt, 25% tt). - How many chromosomes do human gametes have?
Answer: 23 (half of 46).
Tips to Master Chapter 9
- Learn Mendel’s Experiments: Practice monohybrid and dihybrid crosses.
- Draw Punnett Squares: Solve 5 daily—nail those ratios!
- Memorize Terms: Genes, alleles, genotype—make flashcards.
- Understand Sex Determination: XX/XY is a fave exam question.
- Relate to You: Spot traits from your family!
Chapter 9: Heredity is like a detective story about how you got your traits. With these questions and answers, you’re all set to rock your Class 10 Science exams! Keep practicing, stay curious, and you’ll shine. Got doubts? Drop them below—I’m here to help. Happy studying, heredity heroes!
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