CBSE Class 10 · Science · board exam 2027
Chapter 8: Heredity — notes
The chapter’s 6 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. Variation is created and passed on
Okay, so — when living things reproduce, the new ones are similar to their parents.
- • Reproduction creates similar but subtly different individuals
- • Asexual reproduction: very little variation (e.g. bacteria dividing)
- • Sexual reproduction: much greater diversity created
- • Example: sugarcane (little variation) vs animals (distinct variation)
- • Environment selects variants -> basis of evolution
2. Heredity and inherited traits
Okay, so let's talk about heredity.
- • Heredity: rules by which traits are reliably inherited
- • Child inherits basic design but shows variation
- • Father and mother contribute equal genetic material
- • Each trait has two versions in the child
- • Mendel: counted traits across generations in pea plants
3. Mendel's dominant and recessive traits
Okay, so let's talk about Mendel's experiment with pea plants.
- • Cross: Tall x Short pea plants
- • F1 generation: ALL tall (no medium height)
- • F1 self-pollinated -> F2: 3 tall : 1 short
- • Explanation: TT and Tt = tall; tt = short
- • T = dominant trait, t = recessive trait
4. Independent inheritance of two traits
Okay, so Mendel asked another question.
- • Cross: Tall+Round x Short+Wrinkled
- • F1: all Tall, Round seeds (dominant traits)
- • F1 self-pollinated -> F2 shows NEW combinations
- • New types: Tall+Wrinkled, Short+Round
- • Conclusion: traits inherited independently
5. How genes and chromosomes control traits
Okay, so let's see how a gene actually controls a trait.
- • Gene = section of DNA for making one protein
- • Trait example: tallness depends on hormone amount
- • Efficient enzyme -> more hormone -> tall plant
- • Less efficient enzyme -> less hormone -> short plant
- • Genes carried on chromosomes (independent pieces of DNA)
- • Each cell: 2 copies of each chromosome (1 from each parent)
6. Sex determination in human beings
Okay, so let's talk about how a baby's sex gets decided.
- • Women: XX (pair of X chromosomes)
- • Men: XY (one X, one short Y)
- • All children get X from mother
- • Sex depends on father's contribution: X or Y
- • Father's X -> girl; Father's Y -> boy
Summary
Okay, so let's close this chapter. Reproduction gives us individuals similar in basic design, but each one is a little different. Sexual reproduction creates much more variation than asexual reproduction. And the environment decides which of these variants actually survive. Now, heredity — that's just the set of rules by which traits pass reliably from parents to children. Both parents give equal genetic material to the child. Remember Mendel's pea plants? He showed each trait has two copies, called genes. One version, the dominant trait, shows up over the other, the recessive trait. That's why in F2, we got tall to short plants in a 3:1 ratio. His two-trait crosses showed something more — traits like seed shape and plant height are inherited independently of each other. That's what gives new combinations in the offspring. Genes sit on chromosomes, and they control traits by controlling proteins, things like enzymes, which affect stuff like hormone levels. And finally, in human beings, chromosomes decide sex. Women are XX, men are XY. Whether the child gets an X or a Y chromosome from the father — that decides if the baby is a girl or a boy. So tell me — between the mother and the father, who decides the sex of the child?
AskMedha · Medha Ma’am — CBSE Class 10 Science, Chapter 8. Written from the textbook, checked twice.
Questions parents and students ask
- How do I get the "Heredity" notes as a PDF?
- Press "Save as PDF" — the phone’s print sheet opens; choose "Save as PDF" there. The PDF holds the notes only.
- Where are these notes written from?
- From the chapter’s own textbook text, part by part, in the book’s own terms; a second, independent model then checked every part against the book. The full lesson, a check question for each part and the practice are in the AskMedha app.
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