What are Mendel's laws of inheritance and why are they important?

Gregor Mendel, through his experiments on pea plants, formulated the fundamental laws of inheritance. The Law of Dominance states that when two contrasting forms of a trait are present, only one (dominant) is expressed in the first generation while the other (recessive) is hidden. The Law of Segregation states that during gamete formation, the two alleles for a trait separate so that each gamete carries only one allele. The Law of Independent Assortment states that alleles of different traits are distributed independently of each other during gamete formation. These laws form the foundation of genetics and explain how traits are passed from parents to offspring. Mendel's work was revolutionary because it provided a mathematical and systematic explanation for heredity, which had been poorly understood before his experiments.

What is the difference between dominant and recessive traits with examples?

Dominant traits are those that are expressed (visible) in an organism even when only one copy of the dominant allele is present. Recessive traits are expressed only when two copies of the recessive allele are present (homozygous recessive). In Mendel's pea plant experiments, tall plants (T) dominated over short plants (t), meaning even a Tt plant would appear tall. Round seeds (R) dominate over wrinkled seeds (r). Yellow seed colour dominates over green. In humans, brown eye colour is dominant over blue eyes, and free earlobes are dominant over attached earlobes. A person can carry a recessive allele without showing the trait — this is called being a carrier. Dominant traits are represented by capital letters and recessive traits by lowercase in genetic crosses.

How does sex determination happen in humans?

In humans, sex is determined by chromosomes. Humans have 23 pairs of chromosomes — 22 pairs are called autosomes and one pair consists of the sex chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). During reproduction, the mother (XX) always contributes an X chromosome through her egg. The father (XY) can contribute either an X or a Y chromosome through sperm. If a sperm carrying X fertilises the egg, the resulting XX combination produces a female child. If a sperm carrying Y fertilises the egg, the resulting XY combination produces a male child. Therefore, it is the father's chromosome that determines the sex of the child, not the mother's. This makes the idea of blaming the mother for a child's gender scientifically incorrect.

What is the difference between inherited traits and acquired traits?

Inherited traits are characteristics that are passed down from parents to offspring through genes. These traits are encoded in the DNA and can be transmitted to the next generation. Examples include eye colour, blood group, skin colour, height (partially), and the ability to roll one's tongue. Acquired traits are characteristics developed during an individual's lifetime due to environmental influences, experiences, or use and disuse of body parts. These traits are NOT passed on to offspring because they do not involve changes in the DNA of germ cells (sperm and egg). For example, a person who exercises and develops strong muscles will not automatically have muscular children. A bodybuilder's offspring will not be born muscular. Only changes in the DNA present in reproductive cells can be inherited by future generations.

How does evolution relate to heredity and what evidence supports it?

Evolution is the gradual change in the inherited characteristics of populations over successive generations. It is closely linked to heredity because genetic variations arise during reproduction and are passed to offspring. Natural selection acts on these variations — individuals with favourable traits survive and reproduce more, passing those traits on. Over many generations, this causes species to change. Evidence for evolution comes from fossils (which show gradual changes in forms over millions of years), homologous organs (similar structures in different organisms suggesting common ancestry, like the forelimbs of humans, whales, and bats), analogous organs (different structures performing the same function), and molecular evidence (similar DNA and proteins in related species). Mendel's laws explain how traits are inherited, while Darwin's theory of natural selection explains how genetic diversity in a population leads to evolutionary change.

NCERT Solutions for Class 10 Science Chapter 8 Heredity

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NCERT Solutions for Class 10 Science Chapter 8: Heredity

Heredity is the science of how traits are passed from parents to their offspring, and Chapter 8 of Class 10 Science opens the fascinating world of genetics. From Mendel's groundbreaking experiments with pea plants to the molecular structure of DNA, this chapter lays the foundation for understanding how we inherit characteristics like eye colour, blood group, or height. For CBSE board exam preparation, NCERT Solutions for Class 10 Science Chapter 8 — Heredity are a must-study resource.

Myclass24 presents these solutions in a clear, chapter-focused format with easy-to-understand explanations of dominant and recessive traits, monohybrid and dihybrid crosses, sex determination, and the connection between genes and inheritance. If you have struggled with Punnett squares or the law of segregation, these solutions break everything down step by step. Students from all boards who follow the NCERT curriculum will find these solutions extremely useful for their exams.

Download NCERT Solutions for Class 10 Science Chapter 8 Heredity PDF

Download the PDF of NCERT Solutions for Class 10 Science Chapter 8 — Heredity from Myclass24. The PDF includes fully solved exercise questions, Punnett square diagrams, and key definitions. It is mobile-optimised for easy reading on any screen size and includes all in-text questions with answers. Perfect for last-minute board exam revision.

Chapter 8: Heredity — Key Concepts, Facts & Topic Breakdown

Gregor Johann Mendel is called the Father of Genetics. He conducted his famous experiments on Pisum sativum (garden pea) in the 1860s and proposed two laws: the Law of Segregation and the Law of Independent Assortment. His work was rediscovered in 1900, long after his death, and formed the basis of modern genetics.

Mendel's Laws at a Glance

Law	Statement	Example
Law of Dominance	In a cross, dominant allele masks the recessive allele	Tall (T) masks Dwarf (t) in Tt plants
Law of Segregation	Alleles separate during gamete formation	Tt plant produces T and t gametes equally
Law of Independent Assortment	Genes for different traits segregate independently	Applies in dihybrid crosses (e.g., TTGG x ttgg)

Monohybrid Cross — Tall (TT) x Dwarf (tt)

Generation	Cross	Genotype Ratio	Phenotype Ratio
F1	TT x tt	All Tt	All Tall
F2	Tt x Tt	1TT : 2Tt : 1tt	3 Tall : 1 Dwarf

Sex Determination in Humans

Humans have 46 chromosomes (23 pairs); the 23rd pair are sex chromosomes
Females have XX sex chromosomes; Males have XY sex chromosomes
The sex of a child is determined by the father's contribution — X gives girl (XX), Y gives boy (XY)
Chromosomal sex determination also occurs in birds (ZW system), insects, and other organisms differently
Genes are segments of DNA located on chromosomes that carry hereditary information

Key Genetic Terms

Term	Definition
Gene	A segment of DNA that codes for a specific trait
Allele	Alternative forms of a gene (e.g., T for tall, t for dwarf)
Genotype	Genetic composition of an organism (e.g., TT, Tt, tt)
Phenotype	Observable characteristics of an organism (e.g., tall, dwarf)
Dominant	Allele that expresses itself even in heterozygous condition
Recessive	Allele that expresses only in homozygous condition
Homozygous	Both alleles are same (TT or tt)
Heterozygous	Alleles are different (Tt)

Exam-Important Facts — Chapter 8

Mendel selected 7 contrasting traits in pea plants such as seed shape (round/wrinkled), seed colour, flower colour, pod shape, pod colour, flower position, and plant height
Evolution and heredity are linked — inherited variations over generations lead to evolution
Acquired traits (like a scar or a muscle built by exercise) are NOT inherited; only genetic traits are
Blood group in humans is determined by three alleles: IA, IB, and i (multiple allelism)
Haemophilia is a sex-linked disorder carried on the X chromosome