All questions of Heredity and Evolution for Class 10 Exam

The primary function of the flight feathers is to aid in the generation of both thrust and lift, thereby enabling flight. The flight feathers of some birds have evolved to perform additional functions, generally associated with territorial displays, courtship rituals or feeding methods.

Artificial selection is a process in which man selects a particular desired traits for breeding, in order to generate new plants/ animals with improved characters. For e.g. Early farmers cultivated wild cabbage orBrassica oleracea. This wild cabbage developed into many varieties such as cabbage, broccoli, kohlrabi, cauliflower, kale, and brussels. These varieties were artificially selected because of their characteristic traits.

Genetic Drift Means Change In the frequency of gene from Generation to generation.. So D is Correct

Genetic drift (also known as allelic drift or the Sewall Wright effect) is the change in the frequency of an existing gene variant (allele) in a population due to random sampling of organisms. ... A population's allele frequency is the fraction of the copies of one gene that share a particular form.

We only know about extinct groups like dinosaurs, ammonites and trilobites through fossils. Some animals and plant are only known to us as fossils. By studying the fossil record we can tell how long life has existed on Earth, and how different plants and animals are related to each other.

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.

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.

A) 50%

Explanation:

A heterozygous tall plant has the genotype Tt (T for the tall allele and t for the dwarf allele). A homozygous dwarf plant has the genotype tt. When these two plants are crossed, the possible genotypes of the progeny can be determined using a Punnett square.

Tt (heterozygous tall plant)
T | t
---------
t | Tt | tt
t | Tt | tt

As we can see, there are 4 possible outcomes: 2 Tt (tall) and 2 tt (dwarf). So, the proportion of dwarf progeny (tt) is 2 out of the 4 possibilities, which is equal to 50%.

For most DNA sequences, humans and chimpanzees appear to be most closely related, but some point to a human-gorilla or chimpanzee-gorilla clade. The human genome has been sequenced, as well as the chimpanzee genome. Humans have 23 pairs of chromosomes, while chimpanzees, gorillas, and orangutans have 24.

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.

Role of Genes in Controlling Traits
Genes are fundamental units of heredity that play a crucial role in determining the characteristics or traits of an organism. They are segments of DNA that encode specific instructions for the production of proteins, which are essential for the structure and function of cells.
How Genes Influence Traits
- Genes provide the blueprint for protein synthesis: Proteins are vital molecules that perform a myriad of functions in the body, from structural roles in cells to enzymes that catalyze biochemical reactions.
- Expression of traits: The specific combination of genes inherited from parents influences traits such as eye color, height, and susceptibility to certain diseases. Each gene can have different variations, known as alleles, which contribute to the diversity of traits observed in a population.
- Interaction with the environment: While genes provide the foundational information for traits, they often interact with environmental factors. For example, nutrition can impact height, while exposure to sunlight can affect skin color.
Conclusion
In summary, the correct answer is option 'B' because genes provide the information necessary for making proteins that ultimately control traits. This relationship between genes and proteins is fundamental to understanding how biological characteristics are expressed and inherited across generations.

In bat, skin folds are stretched between the elongated fingers and serve the purpose of wings.

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 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.

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.

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.

Introduction to Mendel's Pea Plant Experiments
Gregor Mendel, often referred to as the father of genetics, conducted groundbreaking experiments using pea plants in the 19th century. His work laid the foundation for understanding heredity and the concept of dominant and recessive traits.
Dominant Traits Identified
In his experiments, Mendel observed various traits and their inheritance patterns. Among the traits he studied, one of the key findings was the relationship between dominant and recessive traits.
Round Seed Shape as Dominant
- Mendel found that when he crossed two pea plants with different traits, the offspring exhibited certain predictable patterns.
- The round seed shape (option B) was determined to be dominant over the wrinkled seed shape.
- This means that if a plant had at least one allele for round seeds, it would display the round shape, regardless of the other allele.
Other Traits Considered
- Shortness (option A) is a trait associated with the height of the plant, but it was not dominant in Mendel's findings.
- Green seed color (option C) and wrinkled seed shape (option D) were also traits studied, but they were found to be recessive traits.
Conclusion
Mendel's experiments highlighted the concept of dominant and recessive traits, with round seed shape emerging as the dominant trait. This discovery was pivotal in understanding genetic inheritance and has influenced modern genetics profoundly.

Understanding Artificial Selection
Artificial selection, also known as selective breeding, is a process where humans intentionally choose specific individuals with desirable traits to reproduce. This method contrasts with natural selection, where the environment influences which individuals survive and reproduce.
Key Features of Artificial Selection:
- Human Intervention: In artificial selection, humans play an active role in breeding. They select individuals based on traits that are beneficial or desirable, such as size, color, or yield.
- Desired Traits: The traits selected can range from physical characteristics (like the size of fruits in agriculture) to behavioral traits (like temperament in pets).
- Controlled Breeding: By controlling the breeding process, humans can enhance specific traits over generations, leading to significant changes in the species.
Examples of Artificial Selection:
- Agriculture: Farmers have selectively bred crops to increase yield, resistance to pests, and improve taste. For instance, modern corn varieties are vastly different from their wild ancestors due to selective breeding.
- Animal Breeding: Dogs are a prime example, where various breeds have been developed through artificial selection to exhibit specific traits, such as size, appearance, and behavior.
Implications of Artificial Selection:
- Genetic Diversity: While artificial selection can produce desired traits, it can also reduce genetic diversity within a species, making them more vulnerable to diseases and environmental changes.
- Ethical Considerations: The practice raises ethical questions regarding animal welfare and the long-term impacts on biodiversity.
In summary, artificial selection is a powerful tool that allows humans to shape the characteristics of plants and animals, leading to significant advances in agriculture and pet breeding.

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.

Evolutionary relationships help us to trace who we are more close to and who is our common ancestor. A group of organisms is similar enough to be thought of together by certain characteristics.Thus, the homologous and analogous characteristics help to trace an evolutionary relationship between different species.

Explanation:
Introduction:
The question is asking which sentence is correct regarding the relationship between the age of a fossil and the depth at which it is found. We need to determine which statement accurately describes this relationship.

Analysis:
Let's analyze each option to determine which one is correct:

- Option a: "Age of fossil is not related to the depth where it is found." This statement is incorrect. The age of a fossil is often related to the depth at which it is found because fossils found in deeper layers are generally older than those found near the surface.

- Option b: "Fossil found near earth surface is more recent." This statement is correct. Fossils found near the Earth's surface are usually more recent because they have been deposited more recently and have not been subjected to the same geological processes as fossils found in deeper layers.

- Option c: "Fossil found at deeper layers is more recent." This statement is incorrect. Fossils found in deeper layers are generally older, not more recent. This is because the layers of sedimentary rock that contain fossils are formed over time, with older layers being deposited first and newer layers being deposited on top.

- Option d: "Fossil found in the rocks is more recent." This statement is incorrect. All fossils are found in rocks, so this statement does not provide any information about the relationship between the age of a fossil and the depth at which it is found.

Conclusion:
Based on the analysis, we can conclude that option b is the correct sentence. Fossils found near the Earth's surface are generally more recent because they have been deposited more recently and have not undergone the same geological processes as fossils found in deeper layers.