Class 10 Science Chapter 8 (formerly Chapter 9, Heredity and Evolution; rationalised in 2026-27 as Heredity), explains how variations accumulate across generations, how Gregor Mendel worked out the laws of inheritance using garden pea plants (*Pisum sativum*), how genes control traits through proteins, and how sex is determined in human beings.
What Class 10 Science Chapter 8 Covers
8.1 Accumulation of Variation During Reproduction contrasts variations in asexual reproduction (minor DNA copying inaccuracies, as in a field of sugarcane) with the much greater variations generated by sexual reproduction.
8.2 Heredity & Rules for the Inheritance of Traits – Mendel’s Contributions works through Mendel’s monohybrid cross between tall ($TT$) and short ($tt$) pea plants—giving all tall ($Tt$) in $\text{F}_1$ and a $3:1$ phenotypic ($1:2:1$ genotypic) ratio in $\text{F}_2$—and his dihybrid cross between round-yellow ($RRYY$) and wrinkled-green ($rryy$) seeds giving a $9:3:3:1$ ratio in $\text{F}_2$, demonstrating independent assortment of traits. It also explains how a gene section of DNA codes for an enzyme that produces a plant hormone controlling height.
8.2.4 Sex Determination shows that while environmental temperature determines sex in some reptiles, human sex is genetically determined by the 23rd pair of chromosomes: mothers have $XX$ and always contribute an $X$ chromosome, while fathers have $XY$, so a child inheriting $X$ from the father is a girl ($XX$) and one inheriting $Y$ is a boy ($XY$).
Exercises in Chapter 8
- In-text Questions ask how Mendel’s experiments show that traits may be dominant or recessive, how they show that traits are inherited independently, and how the sex of the child is determined in human beings.
- Chapter Exercises (4 Questions) cover Mendelian dihybrid cross ratios, dominant vs recessive blood group/coat colour inheritance problems, and how equal genetic contribution of male and female parents is ensured in the progeny.
Read Class 10 Science Chapter 8 Online
More Chapters
- Previous: Chapter 7: How do Organisms Reproduce?
- Next: Chapter 9: Light – Reflection and Refraction
- Hindi medium: Class 10 Science Chapter 8 PDF in Hindi (Vigyan)
- All Science chapters and the other Class 10 books: Class 10 NCERT books 2026-27
- All Class 1 to 12 NCERT Textbooks: NCERT Books PDF (Class 1–12)
FAQ
How do Mendel’s experiments show that traits are inherited independently?
In a dihybrid cross between pea plants with round-yellow seeds ($RRYY$) and wrinkled-green seeds ($rryy$), the $\text{F}_2$ generation produces not only the parental combinations but also two new combinations—round-green and wrinkled-yellow—in a $9:3:3:1$ ratio, proving that seed shape and seed colour assort independently.
How is the sex of a child determined in human beings?
Human females have two $X$ chromosomes ($XX$) and males have one $X$ and one $Y$ chromosome ($XY$). All children inherit an $X$ chromosome from their mother; the sex of the child is determined by whether they inherit an $X$ chromosome (girl, $XX$) or a $Y$ chromosome (boy, $XY$) from their father.