Heredity and Evolution — Previous Year Questions (Class 10 Science)
This chapter explores heredity, variation, and evolution. It covers Mendelian genetics, dominant and recessive traits, and the mechanisms of evolution and
TL;DR: This chapter explores heredity, variation, and evolution. It covers Mendelian genetics, dominant and recessive traits, and the mechanisms of evolution…
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This chapter explores heredity, variation, and evolution. It covers Mendelian genetics, dominant and recessive traits, and the mechanisms of evolution and
Heredity and Evolution — Previous Year Questions with Solutions
Q (2023, 3 marks): Define heredity and variation. How are they related to evolution?
Answer: Heredity: The transmission of traits from parents to offspring through genes.
Variation: The differences in traits among individuals of the same species.
Relationship to evolution:
- Heredity ensures traits can be passed through generations
- Variation provides raw material for natural selection
- Beneficial traits accumulate in populations over time
- Over many generations, this leads to evolution and new species formation
- Darwin's natural selection relies on both heredity and variation
Q (2022, 2 marks): State Mendel's law of segregation with an example.
Answer: Mendel's Law of Segregation:
Traits are controlled by pairs of factors (genes). During gamete formation, these factors separate so each gamete receives only one factor of each trait.
Example: Pea plant height
- T = tall (dominant), t = dwarf (recessive)
- Heterozygous plant (Tt) produces gametes with T or t
- During fertilization, factors recombine
- Offspring: TT (tall), Tt (tall), tt (dwarf) in 3:1 ratio
Q (2023, 3 marks): In humans, the ability to taste PTC is dominant. If both parents can taste PTC, what are the possible genotypes and phenotypes of their children?
Answer: Let T = taster (dominant), t = non-taster (recessive)
Parents who can taste PTC can be TT or Tt
Possible crosses:
1. TT × TT → All TT (all children tasters)
2. TT × Tt → TT, Tt (all children tasters)
3. Tt × Tt → TT (25%), Tt (50%), tt (25%)
Phenotypes: 75% tasters, 25% non-tasters (3:1 ratio)
Conclusion:
- If both parents are homozygous (TT), all children will be tasters
- If at least one parent is heterozygous (Tt), there is a 25% chance of non-taster children
Q (2021, 3 marks): Explain Darwin's theory of natural selection.
Answer: Darwin's Theory of Natural Selection:
1. Overproduction: Organisms produce more offspring than environment can support
2. Variation: Individuals show variations in traits
3. Competition: Due to limited resources, organisms compete for survival
4. Differential survival: Individuals with traits suited to environment survive (survival of the fittest)
5. Inheritance: Favorable traits are inherited and passed to offspring
6. Evolution: Over many generations, beneficial traits accumulate, leading to evolution of species
Example: Peppered moths in England
- Light colored moths were common before industrial revolution
- Pollution darkened tree bark
- Dark moths now survived better (camouflage)
- Over time, dark moths became more common
Q (2022, 2 marks): What is the difference between homologous and analogous structures? Give examples.
Answer: Homologous structures:
- Similar in basic structure but different in function
- Derived from common ancestor
- Example: Human arm, bat wing, dolphin flipper, horse leg
- Evidence for evolution
Analogous structures:
- Similar in function but different in structure
- Evolved independently to suit similar environments
- Example: Insect wings and bird wings
- NO evidence for common ancestry
Q (2023, 2 marks): A woman with blood group AB marries a man with blood group O. What are the possible blood groups of their children?
Answer: Blood group genetics:
AB = I^A I^B (genotype)
O = ii (genotype)
Cross: I^A I^B × ii
Possible offspring:
- I^A i (blood group A)
- I^B i (blood group B)
Possible blood groups of children: A and B (50% each)
None will have AB or O blood group
Frequently Asked Questions
What is the difference between a gene and an allele?
A gene is a unit of heredity controlling a trait. An allele is a variant form of a gene. For example, the gene for flower color in peas has alleles for red and white flowers. A gene occupies a specific position on a chromosome.
How is Mendel's law of independent assortment different from the law of segregation?
Law of segregation: Alleles of one trait separate during gamete formation. Law of independent assortment: Alleles of different traits assort independently during gamete formation (applies to genes on different chromosomes).
More Class 10 Science PYQs
- Chemical Reactions and Equations
- Light (Reflection and Refraction)
- Electricity
- Acids, Bases and Salts
- Metals and Non-metals
- Life Processes
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