All questions of Heredity for Class 10 Exam

The DNA in the nucleus of a cell is the information source for making proteins. If the information is changed, different proteins will be made. The basic event in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell and they need to get separated from each other. DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate, each with its own cellular apparatus.

Understanding Genetic Material Exchange
Genetic material exchange is a fundamental process in biological reproduction, particularly significant in the context of sexual reproduction.
What is Sexual Reproduction?
- Sexual reproduction involves the combination of genetic material from two parent organisms.
- It typically requires the formation of gametes (sperm and egg cells) through a process called meiosis.
Mechanism of Genetic Exchange
- During fertilization, a sperm cell merges with an egg cell, resulting in a zygote.
- This zygote contains a unique combination of genes from both parents, contributing to genetic diversity.
Key Benefits of Genetic Exchange
- Genetic Variation: Sexual reproduction promotes genetic diversity, which is crucial for the adaptation and survival of species in changing environments.
- Evolution: The variation introduced through genetic exchange is a driving force in the process of evolution, enabling populations to adapt over generations.
Contrast with Other Reproductive Methods
- Asexual Reproduction:
- Involves a single organism producing offspring identical to itself.
- No exchange of genetic material occurs, leading to clones.
- Vegetative Reproduction:
- A form of asexual reproduction where new plants grow from parts of the parent plant.
- Again, no genetic exchange takes place.
- Budding:
- A type of asexual reproduction where a new organism develops from an outgrowth or bud.
- This method also results in genetically identical offspring.
Conclusion
In summary, sexual reproduction is the only method among the options listed that involves the exchange of genetic material, resulting in genetic diversity and evolutionary potential.

The genotypic ratio in the F2 generation of a monohybrid cross is 1:2:1, corresponding to homozygous dominant, heterozygous, and homozygous recessive individuals, respectively.

Understanding Reproduction
Reproduction is a biological process that ensures the continuation of a species. It can be broadly classified into two types: asexual and sexual reproduction. The method of reproduction significantly influences the genetic diversity of the offspring.
Asexual Reproduction
- In asexual reproduction, a single organism produces offspring without the involvement of gametes (sex cells).
- The offspring are genetically identical to the parent, resulting in little to no variation.
- Common examples include binary fission in bacteria, budding in yeast, and vegetative propagation in plants.
Sexual Reproduction
- In contrast, sexual reproduction involves the fusion of male and female gametes, leading to the formation of a zygote.
- This process introduces genetic variation in offspring due to the combination of genes from two parents.
- Organisms can adapt more effectively to environmental changes due to this genetic diversity.
Why Sexual Reproduction Leads to More Variation
- Genetic Recombination: During meiosis, the process of gamete formation, genetic material is shuffled and recombined, resulting in unique genetic combinations.
- Mutations: Sexual reproduction allows for the introduction of new traits through mutations, which may be beneficial for adaptation.
- Selection Pressure: The variation produced enhances the chances of survival and reproduction in changing environments, as some offspring may possess advantageous traits.
In summary, sexual reproduction is the method that leads to greater variation in offspring compared to asexual reproduction, making option 'B' the correct answer. This genetic diversity is crucial for the evolution and adaptability of species.

The Concept of Heredity
Heredity refers to the biological process through which traits and characteristics are passed down from parents to their offspring. This fundamental concept is crucial in understanding genetics and how living organisms inherit various features.
Key Points about Heredity:
- Transfer of Genetic Information:
- Heredity involves the transmission of genes, which are units of heredity located on chromosomes.
- These genes carry information that determines physical traits, such as eye color, height, and susceptibility to certain diseases.
- Role of DNA:
- Deoxyribonucleic acid (DNA) is the molecule that contains the genetic blueprint for an organism.
- During reproduction, DNA from both parents combines, resulting in a unique genetic makeup for the offspring.
- Mendelian Inheritance:
- The principles of heredity were first systematically studied by Gregor Mendel in the 19th century.
- Mendel’s laws describe how traits are inherited through dominant and recessive alleles.
- Variability and Evolution:
- While heredity ensures that offspring resemble their parents, it also introduces variations due to mutations and recombination.
- This genetic diversity is essential for evolution and adaptation to changing environments.
Conclusion
Understanding heredity is crucial for fields such as medicine, agriculture, and evolutionary biology. It provides insights into how traits are inherited and can influence health and behavior in future generations. In summary, option 'B' accurately represents heredity as the transfer of characteristics from parents to offspring, highlighting its fundamental role in biology.

Understanding Mendel's F2 Generation
Mendel's experiments with pea plants laid the foundation for genetics, especially in understanding inheritance patterns.
Single Trait Inheritance
When studying a single trait, Mendel observed the inheritance of dominant and recessive alleles. In his experiments, he crossed homozygous parents:
- P Generation: One parent with two dominant alleles (AA) and another with two recessive alleles (aa).
- F1 Generation: All offspring (Aa) displayed the dominant trait.
F2 Generation Results
When F1 plants were self-fertilized, the F2 generation emerged, revealing a classic 3:1 phenotypic ratio of dominant to recessive traits:
- Phenotypic Ratio: 3 dominant (AA or Aa) : 1 recessive (aa)
However, when considering the genotypes:
- Genotypic Ratio: This includes:
- 1 homozygous dominant (AA)
- 2 heterozygous (Aa)
- 1 homozygous recessive (aa)
Thus, the genotypic ratio for the F2 generation is:
- 1 AA : 2 Aa : 1 aa
Correct Answer: 1:2:1
This corresponds to option 'B'. The 1:2:1 ratio illustrates the distribution of genotypes resulting from the segregation of alleles during meiosis.
Conclusion
Mendel's work exemplifies the foundational principles of genetic inheritance, with the F2 generation showcasing the predictable ratios of genotypes and phenotypes, crucial for understanding heredity.

Understanding Human Sex Chromosomes
In humans, the determination of biological sex is primarily influenced by the composition of sex chromosomes. Let's break down the key aspects:
Sex Chromosome Composition
- Females (XX): Women have two X chromosomes, which are denoted as XX. This configuration is essential for typical female development and functions in reproduction.
- Males (XY): Men possess one X and one Y chromosome, represented as XY. The presence of the Y chromosome triggers male biological development and characteristics.
Significance of the Y Chromosome
- The Y chromosome carries genes that are critical for male sex determination and sperm production. One of the key genes on the Y chromosome is the SRY gene, which initiates the pathway for male sex differentiation.
Why Other Options are Incorrect
- Option A (Both males and females have two X chromosomes): This statement is false because only females have two X chromosomes. Males have one X and one Y.
- Option B (Males have two Y chromosomes): This is incorrect. Males have one Y chromosome, not two. Having two Y chromosomes is not viable in humans.
- Option D (Sex chromosomes do not affect sex determination): This statement is misleading. Sex chromosomes are crucial for determining biological sex in humans.
Conclusion
Thus, the correct answer is option 'C': Females have two X chromosomes (XX), and males have one X and one Y chromosome (XY). This chromosomal structure is fundamental to our understanding of human biology and reproduction.

Understanding the Dihybrid Cross
A dihybrid cross involves two traits, each governed by different alleles. In Mendel's experiments, he studied pea plants that had two distinct traits. For simplicity, let’s consider seed shape (round vs. wrinkled) and seed color (yellow vs. green).
Parental Generation (P Generation)
- The parental generation consists of true-breeding plants for both traits (e.g., Round Yellow x Wrinkled Green).
- Round (R) and Yellow (Y) are dominant traits, while wrinkled (r) and green (y) are recessive.
Gamete Formation
- Each parent produces gametes with combinations of alleles:
- Round Yellow (RY)
- Wrinkled Green (ry)
F1 Generation
- The offspring from this cross (F1 generation) will all be heterozygous (RrYy) and display the dominant traits (Round Yellow).
F2 Generation and Phenotypic Ratio
- When F1 plants are crossed (RrYy x RrYy), the F2 generation shows a variety of combinations.
- The resulting phenotypes can be broken down as follows:
- Round Yellow (RY) – 9
- Round Green (Rg) – 3
- Wrinkled Yellow (rY) – 3
- Wrinkled Green (rg) – 1
Final Phenotypic Ratio
- The total ratio of phenotypes is 9:3:3:1.
- This ratio indicates that there are 9 Round Yellow, 3 Round Green, 3 Wrinkled Yellow, and 1 Wrinkled Green.
Conclusion
- Thus, the correct answer to the phenotypic ratio of a dihybrid cross in Mendel’s experiments is indeed 9:3:3:1 (option B). This illustrates the principle of independent assortment, where different traits segregate independently during gamete formation.

DNA copying during reproduction creates variations, which can provide different individuals with advantages for survival. These variations are essential for the adaptability and evolution of species.

Mendel performed cross-breeding experiments on garden pea (Pisum sativum).

 Although he studied the inheritance of seven different pairs of contrasting characters in this plant, he considered only one pair at a time. 

He crossed two pea plants having contrasting characters (e.g., tall and dwarf pea plants) by artificial pollination and obtained the hybrids. 

The resulting hybrid plants were then crossed with each other. He obtained the data from these crosses and analyzed the results carefully.

Chromosomes ensure the stability of DNA in the species by carrying genetic material from both parents and restoring the normal chromosome number during reproduction.