Class 10 Science Chapter 8 Question Answers - Heredity

Q1: Explain the process of sexual reproduction in humans. Describe the role of gametes and the significance of genetic variation in offspring.
Ans: Sexual reproduction in humans involves the fusion of male and female gametes to produce offspring with genetic variation.
The process can be summarized as follows:

• Gamete Formation: In males, the testes produce sperm cells (male gametes), while in females, the ovaries produce egg cells (female gametes).
• Fertilization: During sexual intercourse, sperm from the male is deposited in the female reproductive tract. One sperm fuses with one egg during fertilization, forming a zygote.
• Zygote Development: The zygote undergoes multiple divisions through mitosis, forming an embryo. The embryo implants into the uterus and develops into a fetus over nine months.
• Birth: After development, the fetus is delivered through childbirth.

Significance of Genetic Variation:
Genetic variation is crucial for the survival and adaptation of a species. It results from the combination of genetic material from two parents and is essential for the following reasons:

• Increased Adaptability: Genetic variation leads to diverse traits within a population, allowing some individuals to better adapt to changing environmental conditions.
• Disease Resistance: Variation ensures that some individuals may possess genetic traits that provide resistance to diseases, reducing the overall impact of diseases on a population.
• Evolution: Genetic variation is the raw material for evolution. Natural selection acts on variations, favoring traits that provide advantages in specific environments and leading to the accumulation of beneficial changes over generations.

Q2: Differentiate between acquired traits and inherited traits. Provide examples of each, highlighting their role in the process of evolution.
Ans: Acquired Traits and Inherited Traits are two types of characteristics observed in organisms. They have distinct origins and implications for the process of evolution:
Acquired Traits:

• Acquired traits are those that an individual develops during its lifetime as a result of interactions with its environment. These traits are not determined by an organism's genes.
• Acquired traits are not passed on to offspring as they do not involve changes in the genetic material.
• Example: Tanning of skin due to exposure to sunlight, development of muscles through exercise.

Inherited Traits:

• Inherited traits are characteristics that are determined by an organism's genetic makeup, inherited from its parents.
• Inherited traits are passed on to offspring and play a significant role in shaping the genetic diversity within a population.
• Example: Eye color, height, fur color in animals.

Role in Evolution:

• Inherited traits are central to the process of evolution because they provide the raw material for natural selection to act upon.
• Natural selection favors individuals with inherited traits that offer advantages in a specific environment, leading to their increased survival and reproductive success.
• Over generations, advantageous inherited traits become more prevalent in a population, driving evolutionary changes.

Q3: Describe the process of evolution by natural selection. Provide a detailed example to illustrate how natural selection operates in nature.
Ans: Evolution by natural selection is the process by which organisms with favorable variations are more likely to survive, reproduce, and pass on their advantageous traits to the next generation. This process leads to the gradual accumulation of traits that are better suited to a specific environment.
Here's a detailed example to illustrate natural selection:
Example: Peppered Moths and Industrial Melanism

• Before the Industrial Revolution, the peppered moth population in England had mostly light-colored (peppered) moths, which blended well with the light-colored tree bark.
• With the onset of industrial pollution, the tree bark became darkened due to soot, causing the light-colored moths to be more visible to predators.
• A small number of moths had a genetic variation for dark coloration (melanism), which allowed them to blend in with the darkened tree bark.
• As a result, dark-colored moths had a higher chance of surviving and reproducing, passing on the dark color trait to their offspring.
• Over time, the proportion of dark-colored moths increased in the population, while the proportion of light-colored moths decreased.
• When pollution levels decreased after environmental regulations were enacted, the tree bark became lighter again. As a result, the population of light-colored moths began to recover.

This example demonstrates how natural selection favored a trait (dark coloration) that provided a survival advantage in a changing environment. Over generations, the advantageous trait became more common, illustrating the process of evolution through natural selection.

Q4: Explain the role of variations in the process of evolution. How do variations arise, and how do they contribute to the diversity of species?
Ans: Variations are differences in traits or characteristics within a population of organisms. They play a fundamental role in the process of evolution by providing the raw material upon which natural selection acts. Variations arise through different mechanisms and contribute to the diversity of species in the following ways:
Mechanisms of Variation:

• Genetic Variation: Genetic variations result from changes in an organism's DNA, which can occur due to mutations during DNA replication or genetic recombination during sexual reproduction.
• Environmental Factors: External factors such as diet, climate, and exposure to pollutants can lead to variations in traits that affect an organism's phenotype.

Contribution to Diversity:

• Natural Selection: Variations create differences in traits among individuals in a population. Natural selection acts on these variations, favoring traits that provide advantages in specific environments.
• Adaptation: Organisms with advantageous variations are more likely to survive, reproduce, and pass on their traits to the next generation. This leads to the accumulation of adaptations over time.
• Speciation: Accumulated variations, when significant enough, can lead to the formation of new species as populations diverge and become reproductively isolated.

Variations contribute to the diversity of species by ensuring that each individual is unique. This diversity provides a range of responses to changing environmental conditions, increasing the chances of survival for at least some members of the population. Over time, these variations accumulate, leading to the emergence of new species and the overall richness of life on Earth.

Q5: Describe the process of DNA replication. Explain its significance in the transmission of genetic information from one generation to the next.
Ans: DNA replication is the process by which a DNA molecule makes an identical copy of itself. This crucial process ensures the accurate transmission of genetic information from one generation to the next.
The steps involved in DNA replication are as follows:

• Unwinding: The DNA double helix unwinds with the help of enzymes called helicases, creating two single strands.
• Template Strand and Complementary Base Pairing: Each single strand serves as a template for the synthesis of a new complementary strand. Adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).
• DNA Polymerase: Enzymes called DNA polymerases add complementary nucleotides to the growing strand, following the base-pairing rules. DNA polymerase also proofreads and corrects errors during replication.
• Formation of New Strands: DNA polymerase adds nucleotides to the template strands in the 5' to 3' direction. As a result, the two new strands are synthesized in opposite directions: one continuously (leading strand) and the other in fragments (lagging strand).
• Okazaki Fragments: The lagging strand is synthesized in short fragments called Okazaki.
  
  

Q6: Explain the concept of speciation and how it leads to the formation of new species. Provide an example of speciation, highlighting the role of isolation and adaptation in the process.
Ans: Speciation is the process by which new species arise from existing ones over time. It occurs when populations of a single species become genetically distinct and can no longer interbreed due to various factors.
The process of speciation involves the following steps:

• Geographic Isolation: A population becomes physically separated by geographic barriers, such as mountains, rivers, or oceans. This isolation prevents gene flow between the separated populations.
• Genetic Divergence: Isolated populations experience different selective pressures and accumulate genetic differences through mutations, genetic drift, and natural selection. Over time, these differences lead to distinct traits.
• Reproductive Isolation: Accumulated genetic differences can result in reproductive barriers that prevent successful interbreeding between the two populations. This can be due to differences in mating behaviors, mating seasons, or physical incompatibilities.
• Formation of New Species: Once reproductive isolation is established, the two populations are considered separate species. They can no longer exchange genetic material, leading to the formation of distinct species.

Example: Darwin's Finches

• Darwin's finches in the Galápagos Islands provide a classic example of speciation. Different islands had finch populations with varying beak sizes and shapes, adapted to different food sources.
• Over time, geographic isolation led to genetic divergence between the populations, resulting in distinctive beak traits.
• Reproductive isolation occurred due to differences in beak size affecting mating and feeding behaviors.
• The finch populations on different islands became reproductively isolated and genetically distinct, giving rise to multiple species of finches, each specialized for a specific diet and environment.

Q7: Describe the process of selective breeding. Provide an example of a selectively bred organism, highlighting the desired traits and the significance of this process in agriculture or animal husbandry.
Ans: Selective breeding, also known as artificial selection, is a process where humans intentionally choose certain organisms with desirable traits to mate, aiming to pass on those traits to the next generation.
The process involves the following steps:

• Selection: Organisms with desired traits are selected as parents. These traits could be related to size, color, yield, resistance to diseases, or other characteristics.
• Mating: The selected parents are bred to produce offspring with a higher likelihood of inheriting the desired traits.
• Repeat: The best offspring are chosen as the next generation of parents, and the process is repeated over multiple generations to accentuate the desired traits.

Example: Breeding of Dairy Cattle

• Dairy cattle are selectively bred to enhance milk production. Cows that produce higher quantities of milk with optimal fat content are chosen as parents.
• Through successive generations of selective breeding, offspring inherit genes for increased milk production and desirable milk quality.
• Genetic traits for milk yield and quality become more prevalent in the population over time, leading to more productive dairy cattle.

Significance: Selective breeding is significant in agriculture and animal husbandry as it allows humans to modify and improve the traits of plants and animals for specific purposes. It enhances food production, increases yield, improves disease resistance, and produces organisms better suited to human needs.

Q8: Explain the concept of vestigial organs and their role in providing evidence for evolution. Provide examples of vestigial organs in humans and describe their evolutionary significance.
Ans: Vestigial organs are anatomical structures present in an organism that have lost their original function due to evolutionary changes. Despite their reduced or non-functional state, vestigial organs provide valuable evidence for evolution. They suggest that the ancestors of the organisms possessed fully functional versions of these structures, which were adapted to different conditions.
Examples of vestigial organs in humans include:

• Appendix: The human appendix is a small pouch attached to the large intestine. It is thought to have played a role in digesting plant matter in the ancestral diet but is now vestigial, as humans have evolved to rely less on plant-based diets.
• Coccyx (Tailbone): The coccyx is a small bone at the base of the spine. It is a remnant of a tail that was present in early mammals and served various functions, such as balance and mobility.
• Wisdom Teeth: Many people have smaller jaws than their ancestors, leading to inadequate space for wisdom teeth. These vestigial molars were likely useful for chewing a tougher diet but are now often extracted due to dental issues.
• Ear Muscles: Some people possess small muscles in their ears that allow them to move their ears slightly. These muscles were more developed in the ancestors of humans and aided in focusing on sounds.

Evolutionary Significance: The presence of vestigial organs suggests that organisms share common ancestors with adaptations that were beneficial in different environments. As environments changed, some traits became unnecessary or even detrimental, leading to the loss of functionality in certain structures. Vestigial organs provide strong evidence for evolution by demonstrating the process of natural selection acting on ancestral traits as species adapt to new conditions.

Q9: Describe the contributions of Gregor Mendel to the understanding of inheritance. Explain Mendel's laws of inheritance with reference to the monohybrid cross and provide an example.
Ans: Gregor Mendel, often referred to as the "father of modern genetics," conducted groundbreaking experiments with pea plants in the 19th century. His work laid the foundation for our understanding of inheritance and genetics. Mendel's laws of inheritance include the Law of Segregation and the Law of Independent Assortment.

• Law of Segregation: Mendel proposed that each individual possesses two factors (now known as alleles) for each trait, one inherited from each parent. During gamete formation, these alleles segregate (separate) from each other, so each gamete carries only one allele for a given trait.
• Law of Independent Assortment: Mendel discovered that different traits are inherited independently of each other. Alleles for different traits segregate into gametes independently, resulting in a variety of possible combinations in offspring.

Monohybrid Cross Example:
Consider a monohybrid cross between pea plants with the traits of tall (T) and short (t) stems:

• Parent 1 (P1): TT (tall) × Parent 2 (P2): tt (short)
• F1 Generation: All offspring are tall (Tt), showing the dominance of the tall allele.
• F2 Generation: When F1 plants are self-pollinated, the traits segregate in a 3:1 ratio. Three tall plants (Tt or TT) and one short plant (tt) appear.

Mendel's laws provide a fundamental understanding of how traits are inherited and how genetic diversity is maintained within populations.

Q10: Explain the importance of variation and genetic recombination in the process of evolution. Describe the role of crossing over during meiosis and its significance in creating genetic diversity.
Ans: Variation and genetic recombination are essential mechanisms driving the process of evolution, contributing to the diversity and adaptation of species over time. Genetic recombination, specifically crossing over during meiosis, plays a crucial role in generating genetic diversity.

Importance of Variation and Genetic Recombination:

• Variation: Genetic variation results from differences in DNA sequences among individuals. This variation is the raw material upon which natural selection acts, favoring traits that provide advantages in specific environments.
• Adaptation: Genetic recombination, along with mutations and other mechanisms, leads to new combinations of alleles that may confer adaptability to changing conditions.

Crossing Over during Meiosis: Crossing over occurs during prophase I of meiosis and involves the exchange of genetic material between homologous chromosomes.
The steps of crossing over are as follows:

• Homologous Chromosome Pairing: Homologous chromosomes, each with a maternal and paternal copy, pair up.
• Exchange of Genetic Material: Sections of chromatids from one chromosome cross over and exchange with the corresponding section on the other chromosome.
• Recombination: This exchange results in the formation of new combinations of alleles on the chromatids.

Significance of Crossing Over:

• Genetic Diversity: Crossing over shuffles alleles between homologous chromosomes, creating new genetic combinations in offspring.
• Evolutionary Advantage: Genetic diversity generated by crossing over provides a wider range of traits for natural selection to act upon, enhancing a population's adaptability to changing environments.
• Meiotic Nondisjunction: Crossing over helps correct errors in chromosome separation during meiosis, reducing the likelihood of producing gametes with abnormal chromosome numbers.

In summary, variation and genetic recombination, especially crossing over, are vital mechanisms that contribute to the genetic diversity required for the process of evolution. They ensure that populations can adapt and thrive in response to changing environmental conditions.