Class 10 Heredity Mock Test (CBSE)

Topics in Heredity

• Accumulation of variation during reproduction
• Inherited traits
• Mendel's rules for the inheritance of traits
• How traits are expressed
• Sex determination

Heredity practice questions with answers

1. Q1Multiple choice·1 mark
   In a typical Mendel's monohybrid cross between a pure tall pea plant and a pure dwarf pea plant, the percentage of homozygous tall plants in the $F_2$ generation is:

   1. (a)100%
   2. (b)25%
   3. (c)50%
   4. (d)75%
   Show answer and step marks

   1. Correct option: (b) 25%. In the $F_2$ generation of a monohybrid cross, the genotypic ratio is $1(TT) : 2(Tt) : 1(tt)$. Thus, homozygous tall ($TT$) plants constitute $25\%$ of the total offspring.+1

   Answer: (b)
2. Q2Multiple choice·1 mark
   In a cross between a pure-breeding tall pea plant and a pure-breeding dwarf pea plant, all F$_1$ plants are tall. When the F$_1$ plants are self-pollinated, some dwarf plants reappear in the F$_2$ generation. Which explanation is correct?

   1. (a)The dwarf allele is destroyed by the tall allele in the F$_1$ plants.
   2. (b)Dwarf plants arise in the F$_2$ generation because of a new mutation in every F$_2$ seed.
   3. (c)The dwarf allele is present but hidden in the F$_1$ plants, and the two alleles separate during gamete formation so that dwarf plants form when two dwarf alleles meet.
   4. (d)The F$_1$ plants carry only tall alleles, so the dwarf plants must develop from pollen grains alone.
   Show answer and step marks

   1. Correct option: (c) The dwarf allele is present but hidden in the F$_1$ plants, and the two alleles separate during gamete formation so that dwarf plants form when two dwarf alleles meet.+1

   Answer: (c)
3. Q3Assertion and reason·1 mark
   Assertion (A): Muscular strength a person develops through regular exercise is passed on to the offspring. Reason (R): Only the genetic information present in the gametes is inherited by the next generation.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (d) Assertion (A) is false but Reason (R) is true.+1

   Answer: (d)
4. Q4Multiple choice·1 mark
   Cellular DNA is the information source for making proteins in the cell. A specific section of DNA that provides information for one protein is called a:

   1. (a)Trait
   2. (b)Nucleus
   3. (c)Chromosome
   4. (d)Gene
   Show answer and step marks

   1. Correct option: (d) Gene. A gene is a functional unit of heredity and a specific section of DNA that codes for a particular protein responsible for expressing a specific trait.+1

   Answer: (d)
5. Q5Short answer·3 marks
   Explain how the accumulation of variation during reproduction provides a survival advantage to species during environmental changes. Give a suitable example.
   Show answer and step marks

   1. DNA copying during reproduction is not perfectly accurate, so variations arise and accumulate over successive generations.+1
   2. When the environment changes drastically, individuals that happen to carry suitable variations survive and reproduce, so the species is not wiped out completely.+1
   3. Example, any one of: when water temperature rises, a few heat-resistant bacteria in a population survive and carry on the population; green beetles hidden from crows among green leaves survive while red ones are eaten; or any other valid example.+1

   Answer: Errors in DNA copying create variations that accumulate over generations; when the environment changes, individuals with suitable variations survive, so the species continues. Example: heat-resistant bacteria surviving a rise in water temperature.
6. Q6Short answer·3 marks
   Differentiate between inherited traits and acquired traits with one example for each. Give a brief reason why acquired traits are not inherited.
   Show answer and step marks

   1. Inherited traits are controlled by genes and passed from parents to offspring, whereas acquired traits develop during an individual's lifetime due to experience or the environment.+1
   2. Example of an inherited trait, any one of: free or attached earlobes; eye colour; skin colour; or any other valid inherited trait.+0.5
   3. Example of an acquired trait, any one of: low body weight due to starvation; a scar from an injury; learning to swim or ride a bicycle; or any other valid acquired trait.+0.5
   4. Acquired traits are changes in non-reproductive (somatic) tissues and do not change the DNA of germ cells, so they are not passed on to the progeny.+1

   Answer: Inherited traits are controlled by genes and passed from parents to offspring (e.g. attached or free earlobes); acquired traits develop during life (e.g. low weight due to starvation). Acquired traits do not change the DNA of germ cells, so they are not inherited.

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