SUMMARY: The chapter "Heredity and Evolution" in Class 10 Science explores the principles of inheritance and the process of evolution, explaining how traits are passed from one generation to the next and how species evolve over time. KEY TOPICS: Mendel's laws of inheritance, monohybrid and dihybrid crosses, sex determination, evolution and natural selection, speciation, genetic drift, fossils and their significance, human evolution, variations and their role in evolution.
What is the phenotypic ratio of a monohybrid cross between two heterozygous pea plants (Tt)?
A1:2:1
B3:1
C9:3:3:1
D1:1
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Correct answer: Option 2 — 3:1
Q21 Mark
Which of the following is NOT a part of Mendel's laws of inheritance?
ALaw of Segregation
BLaw of Independent Assortment
CLaw of Dominance
DLaw of Genetic Drift
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Correct answer: Option 4 — Law of Genetic Drift
Q31 Mark
In a dihybrid cross of two heterozygous parents (RrYy), what is the expected phenotypic ratio of the offspring?
A3:1
B9:3:3:1
C1:2:1
D1:1
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Correct answer: Option 2 — 9:3:3:1
Q41 Mark
Which of the following determines the sex of a human child?
AX and Y chromosomes
BAutosomes
CMitochondrial DNA
DRibosomal RNA
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Correct answer: Option 1 — X and Y chromosomes
Q51 Mark
What is the primary mechanism by which evolution occurs according to Darwin's theory?
AGenetic Drift
BNatural Selection
CArtificial Selection
DMutation
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Correct answer: Option 2 — Natural Selection
Q61 Mark
Which of the following statements about genetic drift is true?
AIt affects large populations more significantly.
BIt is a non-random change in allele frequencies.
CIt leads to increased genetic variation.
DIt can lead to the fixation of alleles in small populations.
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Correct answer: Option 4 — It can lead to the fixation of alleles in small populations.
Q71 Mark
What type of evidence do fossils provide in the study of evolution?
ADirect evidence of genetic material
BEvidence of extinct species and evolutionary changes
CEvidence of current species' behavior
DEvidence of environmental changes only
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Correct answer: Option 2 — Evidence of extinct species and evolutionary changes
Q81 Mark
Which of the following is an example of speciation?
AA population adapting to a new environment
BTwo species evolving from a common ancestor
CA species becoming extinct
DA species migrating to a different habitat
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Correct answer: Option 2 — Two species evolving from a common ancestor
Q91 Mark
In pea plants, the allele for tall stems (T) is dominant over the allele for short stems (t). What will be the genotype of a homozygous tall plant?
ATT
BTt
Ctt
DTt or TT
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Correct answer: Option 1 — TT
Q101 Mark
What is the significance of variations in a population?
AThey decrease the chances of survival.
BThey are essential for natural selection.
CThey have no impact on evolution.
DThey only occur in asexual reproduction.
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Correct answer: Option 2 — They are essential for natural selection.
Q111 Mark
Which of the following best describes the term 'speciation'?
AThe process of natural selection
BThe formation of new and distinct species
CThe extinction of a species
DThe adaptation of species to their environment
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Correct answer: Option 2 — The formation of new and distinct species
Q121 Mark
What is the expected outcome of a cross between a homozygous dominant (AA) and a homozygous recessive (aa) organism?
AAll offspring will be homozygous dominant.
BAll offspring will be heterozygous.
CAll offspring will be homozygous recessive.
DOffspring will show a 1:1 ratio of genotypes.
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Correct answer: Option 2 — All offspring will be heterozygous.
Q131 Mark
Which of the following is a key factor in the process of natural selection?
AOverproduction of offspring
BUniformity of traits
CLack of competition
DAbsence of environmental changes
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Correct answer: Option 1 — Overproduction of offspring
Q141 Mark
What role do fossils play in understanding human evolution?
AThey provide insights into dietary habits.
BThey show the physical changes over time in human ancestors.
CThey indicate the genetic makeup of ancient humans.
DThey have no relevance to human evolution.
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Correct answer: Option 2 — They show the physical changes over time in human ancestors.
Q151 Mark
Which of the following is an example of a trait that is inherited through Mendelian genetics?
AIntelligence
BHeight
CFlower color in pea plants
DSkin color in humans
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Correct answer: Option 3 — Flower color in pea plants
Short Answer Questions10 questions
Q163 Marks
What is Mendel's first law of inheritance, and how does it apply to monohybrid crosses?
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Mendel's first law, the Law of Segregation, states that during gamete formation, the two alleles for a trait segregate from each other. In a monohybrid cross, this means that offspring receive one allele from each parent, resulting in a 3:1 phenotypic ratio in the F2 generation.
Q173 Marks
Explain the concept of a dihybrid cross and its significance in understanding inheritance patterns.
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A dihybrid cross examines the inheritance of two different traits simultaneously. It demonstrates Mendel's second law, the Law of Independent Assortment, which states that alleles for different traits segregate independently during gamete formation, resulting in a phenotypic ratio of 9:3:3:1 in the F2 generation.
Q183 Marks
What are sex-linked traits, and how are they inherited?
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Sex-linked traits are associated with genes located on the sex chromosomes, typically the X chromosome. Inheritance of these traits often shows different patterns in males and females, as males have one X and one Y chromosome, while females have two X chromosomes, leading to conditions like color blindness being more common in males.
Q193 Marks
Define evolution and explain the role of natural selection in this process.
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Evolution is the change in the heritable traits of biological populations over successive generations. Natural selection is a mechanism of evolution where organisms better adapted to their environment tend to survive and reproduce, passing on advantageous traits to the next generation.
Q203 Marks
What is speciation, and what are the main types of speciation?
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Speciation is the process by which new species arise from existing ones. The main types include allopatric speciation, which occurs due to geographic isolation, and sympatric speciation, which occurs without geographic separation, often through mechanisms like polyploidy in plants.
Q213 Marks
Describe genetic drift and its potential impact on small populations.
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Genetic drift is a random change in allele frequencies in a population, which can lead to significant evolutionary changes, especially in small populations. It can result in the loss of genetic diversity and increase the likelihood of extinction due to environmental changes.
Q223 Marks
What is the significance of fossils in understanding evolution?
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Fossils provide crucial evidence for the history of life on Earth, showing how species have changed over time and revealing transitional forms that illustrate evolutionary processes. They help scientists understand the timeline of evolution and the relationships between different organisms.
Q233 Marks
Explain the concept of variations and their importance in the process of evolution.
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Variations are differences in traits among individuals within a population, caused by genetic mutations and environmental factors. They are crucial for evolution as they provide the raw material for natural selection, allowing populations to adapt to changing environments over time.
Q243 Marks
What evidence supports the theory of human evolution?
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Evidence for human evolution includes fossil records showing transitional forms, genetic similarities with other primates, and archaeological findings that illustrate the development of tools and culture. These collectively indicate a gradual change from common ancestors to modern humans.
Q253 Marks
How do Mendel's experiments with pea plants contribute to our understanding of heredity?
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Mendel's experiments with pea plants established foundational principles of heredity, including the concepts of dominant and recessive traits. His systematic approach to crossbreeding and careful observation of traits led to the formulation of the laws of inheritance, which are still relevant in genetics today.
Long Answer Questions6 questions
Q266 Marks
Explain Mendel's law of segregation and how it applies to monohybrid crosses. Provide an example to illustrate your explanation.
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Mendel's law of segregation states that during the formation of gametes, the two alleles for a trait separate from each other, so that each gamete carries only one allele for each gene. In a monohybrid cross, where we consider one trait, such as flower color in pea plants (purple vs. white), this law can be illustrated. For example, if we cross a homozygous purple flower (PP) with a homozygous white flower (pp), the F1 generation will all be heterozygous (Pp) and exhibit the dominant trait (purple). When these F1 plants are crossed, the F2 generation will show a phenotypic ratio of 3:1 (purple to white), demonstrating the segregation of alleles during gamete formation.
Q276 Marks
Describe the process of dihybrid crosses and explain how Mendel's law of independent assortment is demonstrated through this type of cross.
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Dihybrid crosses involve two traits that are being studied simultaneously, such as seed shape (round vs. wrinkled) and seed color (yellow vs. green) in pea plants. Mendel's law of independent assortment states that alleles for different traits segregate independently of one another during gamete formation. For example, when crossing two heterozygous plants (RrYy x RrYy), the resulting offspring can exhibit a phenotypic ratio of 9:3:3:1 for the four possible combinations of traits (round yellow, round green, wrinkled yellow, wrinkled green). This demonstrates that the inheritance of one trait does not influence the inheritance of another, supporting the law of independent assortment.
Q286 Marks
Discuss the concept of sex determination in humans and explain the role of the X and Y chromosomes in this process.
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In humans, sex determination is primarily governed by the presence of X and Y chromosomes. Females typically have two X chromosomes (XX), while males have one X and one Y chromosome (XY). During fertilization, the sex of the offspring is determined by the sperm cell, which can carry either an X or a Y chromosome. If the sperm carries an X chromosome, the resulting zygote will be female (XX), and if it carries a Y chromosome, the zygote will be male (XY). This chromosomal mechanism of sex determination is crucial for understanding genetic inheritance and the development of sexual characteristics in humans.
Q296 Marks
Explain the theory of natural selection and its significance in the process of evolution.
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The theory of natural selection, proposed by Charles Darwin, posits that individuals with traits that are better suited to their environment are more likely to survive and reproduce. This process leads to the gradual evolution of species as advantageous traits become more common in the population over generations. Natural selection acts on existing variations within a population, favoring those that enhance survival and reproductive success. Its significance lies in its ability to explain the adaptation of organisms to their environments and the diversity of life forms observed in nature, providing a scientific basis for the understanding of evolution.
Q306 Marks
Define speciation and describe the different mechanisms through which it can occur.
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Speciation is the evolutionary process by which new biological species arise. It can occur through several mechanisms, including allopatric speciation, where populations are geographically isolated, leading to reproductive isolation and divergence over time. Sympatric speciation occurs when new species arise within the same geographic area, often due to behavioral or ecological differences. Additionally, parapatric speciation involves populations that are partially separated and experience different selective pressures. Each of these mechanisms contributes to the diversity of life by creating new species adapted to their specific environments.
Q316 Marks
What is genetic drift, and how does it differ from natural selection in the context of evolution?
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Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies within a population, particularly in small populations. Unlike natural selection, which is a non-random process favoring advantageous traits, genetic drift can lead to the loss of genetic variation and may result in traits becoming fixed or lost purely by chance. For example, if a natural disaster randomly eliminates a portion of a population, the remaining individuals may not represent the original genetic diversity. This randomness can have significant evolutionary consequences, especially in small populations, where genetic drift can lead to rapid changes in allele frequencies.
Assertion–Reason Questions8 questions
Q321 Mark
Assertion (A): Mendel's law of segregation states that alleles for a trait separate during gamete formation.
Reason (R): This law explains how offspring inherit one allele from each parent.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q331 Mark
Assertion (A): A dihybrid cross involves two traits that are inherited independently.
Reason (R): This is demonstrated by Mendel's experiments with pea plants.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q341 Mark
Assertion (A): Sex determination in humans is solely based on the X chromosome.
Reason (R): Males have XY chromosomes while females have XX chromosomes.
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Correct answer: Option 3 —
A is true, but R is false.
Q351 Mark
Assertion (A): Natural selection leads to the survival of the fittest in a population.
Reason (R): This process results in the elimination of less adapted individuals.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q361 Mark
Assertion (A): Genetic drift has a more significant effect in large populations than in small populations.
Reason (R): In small populations, random events can lead to larger changes in allele frequencies.
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Correct answer: Option 4 —
A is false, but R is true.
Q371 Mark
Assertion (A): Fossils provide evidence for the theory of evolution.
Reason (R): They show the changes in species over geological time.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q381 Mark
Assertion (A): Human evolution is a linear process leading to modern humans.
Reason (R): Evolution is a branching process with many species coexisting at different times.
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Correct answer: Option 4 —
A is false, but R is true.
Q391 Mark
Assertion (A): Variations in a population are essential for natural selection to occur.
Reason (R): Without variations, all individuals would have the same fitness level.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Statement-Based Questions8 questions
Q401 Mark
Statement 1: Mendel's law of segregation states that alleles segregate independently during gamete formation.
Statement 2: A dihybrid cross involves two traits and follows the 9:3:3:1 phenotypic ratio.
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Correct answer: Option 1 —
Both statements are true.
Q411 Mark
Statement 1: Sex determination in humans is primarily influenced by the X and Y chromosomes.
Statement 2: All organisms have the same number of chromosomes in their body cells.
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Correct answer: Option 3 —
Only Statement 2 is true.
Q421 Mark
Statement 1: Natural selection is a process that leads to the evolution of species over time.
Statement 2: Genetic drift has no impact on small populations.
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Correct answer: Option 2 —
Only Statement 1 is true.
Q431 Mark
Statement 1: Fossils provide evidence for the evolutionary history of organisms.
Statement 2: Mendel's experiments were conducted on pea plants, which are not suitable for genetic studies.
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Correct answer: Option 2 —
Only Statement 1 is true.
Q441 Mark
Statement 1: Variations in a population are essential for the process of evolution.
Statement 2: Speciation can occur due to geographical isolation of populations.
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Correct answer: Option 1 —
Both statements are true.
Q451 Mark
Statement 1: A monohybrid cross examines the inheritance of a single trait.
Statement 2: The phenotypic ratio of a monohybrid cross is 3:1.
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Correct answer: Option 1 —
Both statements are true.
Q461 Mark
Statement 1: Human evolution is a linear process leading to modern humans.
Statement 2: The concept of common descent suggests that all species share a common ancestor.
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Correct answer: Option 3 —
Only Statement 2 is true.
Q471 Mark
Statement 1: Mendel's law of independent assortment applies to traits located on different chromosomes.
Statement 2: Dihybrid crosses can show a phenotypic ratio of 1:2:1.
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Correct answer: Option 2 —
Only Statement 1 is true.
