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.

Correct answer is:- (d) tall with round seeds

explanation:- since T and R are dominant traits and t and r are ressassive traits. So tall and round are dominant that's why they hide the identity of dwarf and wrinkled so that the seeds looks tall and round.

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.

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

Understanding Monohybrid Crosses
In genetics, a monohybrid cross involves studying the inheritance of a single trait. The classic example is the pea plant experiments conducted by Gregor Mendel.
F1 Generation
In a typical monohybrid cross, two homozygous parents are crossed. For instance, if we cross a tall pea plant (TT) with a short one (tt):
- All offspring (F1) will be heterozygous (Tt) and exhibit the dominant trait (tall).
F2 Generation Creation
When these F1 plants (Tt) are self-fertilized, the next generation (F2) is produced:
- Tt x Tt
Possible Gametes
Each parent can produce two types of gametes:
- T (dominant allele)
- t (recessive allele)
Genotypic Combinations
When we combine these gametes, we can form a Punnett square:
- TT (homozygous dominant)
- Tt (heterozygous)
- Tt (heterozygous)
- tt (homozygous recessive)
Genotypic Ratio
The resulting genotypic ratio from the Punnett square is:
- 1 TT: 2 Tt: 1 tt
This means for every four offspring, one will be homozygous dominant, two will be heterozygous, and one will be homozygous recessive.
Conclusion
Thus, the correct answer for the genotypic ratio of the F2 generation in a monohybrid cross is 1:2:1, which is option 'C'.
This ratio highlights the predictable patterns of inheritance that Mendel discovered through his meticulous experiments.

Mendel's success in discovering the laws of inheritance can be attributed to several factors, but the most important one is his approach to experimentation. His approach was unique and different from the contemporary methods of experimentation.

Consideration of one character at a time:
Mendel focused on studying one trait at a time, rather than studying multiple traits simultaneously. This allowed him to maintain a clear focus on the traits he was studying and avoid confusion caused by multiple traits. He chose to study pea plants, which have seven distinct traits that can be easily identified and studied. By choosing to study one trait at a time, Mendel was able to identify patterns of inheritance that were not noticeable before.

Qualitative analysis of data:
Mendel used a qualitative analysis of data, which means he focused on identifying the presence or absence of a trait rather than measuring the quantity of the trait. This approach allowed him to identify clear and distinct patterns of inheritance. He counted the number of offspring with a particular trait and used statistical analysis to determine the ratios of dominant and recessive traits in the offspring.

Observation of distinct inherited traits:
Mendel observed seven distinct inherited traits in pea plants, including seed color, seed shape, flower color, and plant height. He carefully observed the traits and recorded his findings. This allowed him to identify patterns of inheritance that were not noticeable before.

His Knowledge of biology:
Mendel had a good understanding of biology, which helped him to interpret his findings and draw conclusions about patterns of inheritance. He was familiar with the concepts of genetics, heredity, and variation. This knowledge allowed him to design experiments that were effective in studying inherited traits.

In conclusion, Mendel's success can be attributed to his focus on studying one trait at a time, qualitative analysis of data, observation of distinct inherited traits, and his knowledge of biology. These factors allowed him to discover the laws of inheritance, which revolutionized the field of genetics.

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.

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.

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.

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.