Mendel's Experiment Class 10 in 3D: Monohybrid, Dihybrid and Sex Determination
Mendel's Experiment Class 10 in 3D: Monohybrid, Dihybrid and Sex Determination
Mendel's experiment for Class 10 is a pea plant cross: a tall plant crossed with a short one gives all-tall offspring, and when those offspring self-pollinate, one quarter of the next generation comes out short. From that single result Mendel worked out that every trait is controlled by two copies of a factor, now called a gene, and that one copy can hide the other.
This guide follows the current NCERT chapter on Heredity: both pea crosses, how traits are expressed, sex determination, the diagrams to draw, and the mistakes that cost marks.
What the NCERT Chapter Covers Now
In the current NCERT textbook (Reprint 2026-27), Chapter 8 is titled simply Heredity and runs six pages:
| Section | What it covers |
|---|---|
| 8.1 Accumulation of variation | Why sexual reproduction creates more diversity than asexual reproduction |
| 8.2.1 Inherited traits | Activity 8.1, the free and attached earlobe survey |
| 8.2.2 Mendel's contributions | The monohybrid and dihybrid pea crosses |
| 8.2.3 How traits get expressed | Genes, proteins, and why each germ cell carries one gene set |
| 8.2.4 Sex determination | X and Y chromosomes in humans |
Older notes titled "Heredity and Evolution" cover evolution, speciation and fossils. That material is not in this chapter any more.
The chapter's box on Gregor Johann Mendel (1822 to 1884) makes one point worth remembering: others had studied peas before him, but Mendel was the first to keep count of how many individuals showed a trait in each generation. He used contrasting pea characters: round or wrinkled seeds, tall or short plants, white or violet flowers.
The Monohybrid Cross: Tall x Short
This is Figure 8.3 in the textbook, and it is the diagram you are most likely to be asked to draw.
- Parents: a pure tall plant (TT) is crossed with a pure short plant (tt).
- F1 generation: every plant is tall. There are no medium-height plants. All F1 plants are Tt.
- F2 generation: the F1 plants self-pollinate. Each F1 plant makes germ cells carrying either T or t.
Build the F2 grid from those germ cells:
| T (from one parent) | t (from one parent) | |
|---|---|---|
| T | TT (tall) | Tt (tall) |
| t | Tt (tall) | tt (short) |
So three out of four F2 plants are tall and one is short. That is the 3:1 phenotypic ratio. The genotypes come out as TT, Tt and tt in a 1:2:1 ratio, which is exactly what Activity 8.2 asks you to think about.
The key conclusion, in NCERT's words: a single copy of T is enough to make the plant tall, while both copies have to be t for it to be short. T is the dominant trait and t is the recessive trait.
The Dihybrid Cross: Two Traits at Once
Figure 8.5 follows two traits together, seed shape and seed colour.
- Parents: RRyy (round, green) crossed with rrYY (wrinkled, yellow).
- F1: all RrYy, round and yellow. So round and yellow are dominant.
- F2: each F1 plant makes four kinds of germ cells: RY, Ry, rY and ry. A 4 x 4 grid of these gives 16 combinations.
The F2 includes combinations neither parent had, which shows that seed shape and seed colour are inherited independently.
Fact check: In NCERT's dihybrid cross (Figure 8.5), the F2 generation of 556 seeds splits into 315 round yellow, 108 round green, 101 wrinkled yellow and 32 wrinkled green seeds, which the figure presents as a 9:3:3:1 ratio out of 16. Source: NCERT, Science Class X, Chapter 8 Heredity (Reprint 2026-27)
How Traits Get Expressed
A gene is a section of DNA that carries the information for one protein. NCERT's example: plant height depends on a growth hormone made with the help of an enzyme. If the gene for that enzyme is altered and the enzyme works less efficiently, less hormone is made and the plant is short.
Why can seed shape and colour separate? Because genes sit on separate pieces of DNA called chromosomes. Every germ cell takes one chromosome from each pair, and fertilisation restores the full number.
Sex Determination in Humans
Humans have 22 pairs of matching chromosomes plus one pair of sex chromosomes. Women have XX. Men have XY, where Y is the shorter one.
Every child gets an X from the mother, so the father's chromosome decides the sex: an X gives a girl, a Y gives a boy (Figure 8.6).
What a 3D View Adds
- Chromosomes separating into germ cells makes it obvious why a gamete carries T or t, never both.
- Independent sorting of the shape and colour chromosomes explains the four dihybrid gamete types better than a list of letters.
- X and Y side by side shows the size difference the chapter describes in words.
For the cell structures behind all of this, see our guide to plant cell vs animal cell in 3D.
Where 3D Does Not Help
In the exam you draw the cross and work out the ratio by hand. A 3D model does not do that for you. Mendel's ratios are also statistical: NCERT's own 556-seed count is close to 9:3:3:1, not exact. The earlobe survey in Activity 8.1 teaches that better than any model, because you collect real, messy counts from your own class.
Common Mistakes That Cost Marks
- Calling 3:1 the genotypic ratio. 3:1 is phenotypic. The genotypic ratio is 1:2:1.
- Writing a germ cell as Tt. Germ cells carry one copy: T or t.
- Missing gamete types in the dihybrid cross. List all four: RY, Ry, rY, ry.
- Saying the mother decides the child's sex. The mother always gives X. The father's X or Y decides.
- Treating "dominant" as "more common". Dominance is about which trait is expressed, not how many people have it. The chapter's blood group question tests exactly this.
Check Yourself
- A Tt pea plant self-pollinates. What fraction of its offspring will be short? (One quarter.)
- Why does a germ cell carry only one copy of each gene? (So that fertilisation restores two copies, not four.)
- In the cross RRyy x rrYY, why are all F1 seeds round and yellow? (Both round and yellow are dominant, and every F1 seed carries one of each.)
- Which parent's chromosome decides whether a human baby is a boy or a girl? (The father's.)
Making a Mendel Experiment Project
- Bead or seed draw. Put equal numbers of two colours of beads, or dried green and yellow peas, in two bags to stand for T and t germ cells. Draw one from each bag 40 times and tally the pairs. Expect something close to 1:2:1.
- Class trait survey. Extend Activity 8.1 by recording earlobe type for students and their parents, then propose a rule.
Exercise 3 in the chapter, a project to find the dominant coat colour in dogs, is another good brief.
How VidyaXR Fits
VidyaXR is a browser-based 3D learning platform for NCERT Class 9 and 10 science.
- Class 10 biology in 3D: cells and organ structures you can rotate and look inside, matching the Class 10 biology 3D diagrams you draw in the exam.
- Check the chapter list during the free trial to see which heredity visuals are available before relying on them.
- Any browser, no headset: phone, tablet or laptop, with a free 14-day trial and no credit card.
Next read: the virtual biology lab for Class 10.
Free Resources for Heredity
- NCERT's Heredity chapter is free as a PDF from ncert.nic.in. Read Figures 8.3, 8.5 and 8.6 closely.
- PhET's Gene Expression Essentials shows how a gene is read to make a protein (section 8.2.3).
- DIKSHA links NCERT video explanations to the QR codes in your textbook.
- OLabs (olabs.edu.in), the government-funded online lab platform, is worth checking when the site is up.
Frequently Asked Questions
What is Mendel's experiment in Class 10?
Mendel crossed pure tall and pure short pea plants. All F1 plants were tall, and one quarter of the F2 plants were short, showing that each trait has two gene copies and one can be dominant.
What is the ratio in Mendel's monohybrid cross?
3 tall to 1 short (phenotypic), and 1 TT to 2 Tt to 1 tt (genotypic).
What is the ratio in Mendel's dihybrid cross?
9:3:3:1 for round yellow, round green, wrinkled yellow and wrinkled green. NCERT's figure counts 315, 108, 101 and 32 out of 556 seeds.
How is the sex of a child determined in humans?
The mother always passes an X. An X from the father gives a girl, a Y gives a boy.
Is evolution part of the Class 10 Heredity chapter?
Not in the current NCERT textbook. The 2026-27 reprint covers variation, Mendel's experiments, gene expression and sex determination only.
Conclusion
Mendel's experiment comes down to two copies of every gene, one copy in every germ cell, and dominant traits hiding recessive ones. Learn Figures 8.3, 8.5 and 8.6, practise the grids by hand, and use a 3D view to see why the ratios work.
Explore Class 9 and 10 biology in 3D. Try VidyaXR free for 14 days. No credit card, no headset needed.