Heredity Class 10 Science Handwritten Notes

The Heredity Class 10 Science handwritten notes are scanned, boxed and built for fast last-minute revision, fully matched to the 2026-27 CBSE syllabus. They cover Mendel's experiments, dominant and recessive traits, the monohybrid and dihybrid crosses, the rules of inheritance, and how the sex of a child is decided, all in clear ruled-page form with hand-drawn Punnett squares and labelled crosses.

• CBSE Weightage: 4 to 6 marks from the World of the Living unit, often as 3-mark and 5-mark questions on Mendel's crosses, the F1 and F2 ratios and sex determination.
• Boxed definitions and a hand-drawn Punnett square for every cross, ratio and term the board paper asks about.
• Pairs with the NCERT Solutions, Notes and Book PDF linked lower on this page.

These Heredity handwritten notes are prepared from the official NCERT Science textbook and matched to the 2026-27 CBSE syllabus.

What These Heredity Handwritten Notes Include

These Heredity handwritten notes condense the whole chapter into 21 scanned pages of ruled paper, with every cross drawn by hand and every key term underlined. The pages are built around the three big ideas that the CBSE board paper tests:

• Traits and variation: what heredity means, inherited versus acquired traits, and why variation appears.
• Mendel's experiments: monohybrid and dihybrid crosses on pea plants, the F1 and F2 results, the 3:1 and 9:3:3:1 ratios.
• Inheritance and sex: dominant and recessive alleles, the rules of inheritance, and how chromosomes decide a child's sex.

Heredity Class 10 Science Video Lecture

Source: Magnet Brains on YouTube

Heredity, Traits and Variation: The First Page of the Notes

The opening page settles the most basic board question: what heredity is and how an inherited trait differs from an acquired one. Heredity is the passing of characters, or traits, from parents to their offspring through the genes.

• Heredity: the transmission of traits across generations through the DNA in the genes.
• Inherited trait: a character passed on through the germ cells, like eye colour or ear-lobe type; it reaches the next generation.
• Acquired trait: a change gained during life in the body cells, like low body weight from poor diet; it is not passed on.

Acquired traits are not inherited (a favourite reasoning question): a change in a body (somatic) cell does not reach the germ cells that make the next generation, so only changes in germ-cell DNA can be passed down.

• Variation: the small differences between parents and offspring, and among the offspring.
• Source: sexual reproduction mixes two parents' genes, giving more variation than asexual reproduction.
• Exam line: variation is the raw material of evolution, useful at the species level.

Mendel's Monohybrid Cross and the 3:1 Ratio

The notes draw Mendel's monohybrid cross as a labelled Punnett square; the F2 ratio is a top 3-mark question. The cross below uses tall (T) and short (t) pea plants.

The sharpest point students miss: the short trait disappears in F1 but returns in F2, proving the short factor was hidden, not lost. The two ratios examiners check first:

• Phenotypic ratio: 3 tall : 1 short in F2.
• Genotypic ratio: 1 TT : 2 Tt : 1 tt in F2.
• Why it matters: tall (T) is dominant and short (t) recessive, so a single T makes the plant tall.

Exam line: a recessive trait shows up only when both alleles are recessive (tt). The monohybrid cross proves the two alleles separate during gamete formation, the law of segregation.

Dihybrid Cross and the 9:3:3:1 Ratio in the Notes

The dihybrid cross follows two traits at once, such as seed shape and colour, a common 5-mark question. The cross uses round-yellow (RRYY) and wrinkled-green (rryy) pea seeds.

• Parents (P): round yellow (RRYY) crossed with wrinkled green (rryy).
• F1 generation: all seeds round and yellow (RrYy), the dominant traits.
• F2 generation: four seed types in the ratio 9 round-yellow : 3 round-green : 3 wrinkled-yellow : 1 wrinkled-green.

The big idea the board rewards: the new combinations in F2. Round-green and wrinkled-yellow seeds were absent in the parents, proving the two traits are inherited independently.

• Law of independent assortment: the alleles of one trait separate independently of those of another during gamete formation.
• The 9:3:3:1 ratio: the F2 phenotypic ratio in a dihybrid cross.

How Traits Are Inherited: Genes, Alleles and Rules

This spread settles the vocabulary the board tests by name: define a gene, an allele or the difference between genotype and phenotype.

• Gene: a unit of DNA on a chromosome that controls a trait, such as plant height.
• Allele: one of the two forms of a gene (T for tall, t for short); one comes from each parent.
• Dominant allele: shows its effect even in a single copy (T in Tt).
• Recessive allele: shows only when both copies are recessive (tt).

The difference students mix up most, genotype versus phenotype:

Exam line: TT and Tt look the same (tall), but their genotypes differ. A tall plant can be pure (TT) or hybrid (Tt), so the recessive trait can reappear later.

Sex Determination in Humans

How the sex of a child is decided is a guaranteed 2 to 3-mark question. Humans have 23 pairs of chromosomes, one pair being the sex chromosomes.

• Female: two X chromosomes (XX), so every egg carries an X.
• Male: one X and one Y (XY), so half the sperms carry X and half carry Y.
• Deciding factor: the egg always gives an X, so the sperm decides the child's sex.

• X sperm + X egg: gives XX, so the child is a girl.
• Y sperm + X egg: gives XY, so the child is a boy.
• The ratio: equal chance of a boy or a girl, about 50:50.

Exam point: the sex of the child is decided by the father, because the mother can give only an X chromosome. This corrects the common myth that the mother is responsible for the baby's sex.

Common Mistakes These Notes Help You Avoid

A few errors cost marks every year, mostly from mixing up genotype with phenotype or writing the wrong F2 ratio.

The exam rewards exact terms and correct ratios, so always name the alleles, draw the Punnett square and state the ratio.

How These Notes Pair with the Solutions and Book PDF

These handwritten notes are a revision layer. Use them with the other resources for the same chapter, linked in the table below.

Tip: redraw the monohybrid and dihybrid Punnett squares once from memory, then write the 3:1 and 9:3:3:1 ratios beside them.

All Class 10 Science Handwritten Notes by Chapter

The table links the handwritten notes for every chapter in Class 10 Science. Heredity is highlighted.

FAQs on Heredity Handwritten Notes