Briefly mention the contribution of T.H. Morgan in genetics.
Solution and Explanation
Top Questions on Principles of Inheritance and Variation
- Assertion (A): A male individual always inherits haemophilia from his mother.
Reason (R): The gene for haemophilia lies on X-chromosome.- CBSE CLASS XII - 2025
- Biology
- Principles of Inheritance and Variation
In a certain population, the frequency of three genotypes is as follows:
Genotypes: PP Pp pp
Frequency: 22% 62% 16%
Choose the option that shows the frequency of P and p alleles correctly:- CBSE CLASS XII - 2025
- Biology
- Principles of Inheritance and Variation
- Which of the following conditions correctly describes the manner of determining the sex in the given options?
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- Biology
- Principles of Inheritance and Variation
- Answer the following questions:
- Write the scientific name of the fruit fly.
- Why did Morgan prefer to work with fruit flies for his experiments? State two reasons.
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- Biology
- Principles of Inheritance and Variation
- Assertion (A): Human male is referred to as heterogametic.
Reason (R): The male produces millions of sperms of the same kind.- CBSE CLASS XII - 2025
- Biology
- Principles of Inheritance and Variation
Questions Asked in CBSE CLASS XII exam
Study the following graph carefully and answer the following questions
- CBSE CLASS XII - 2025
- Population Geography
Study the map of the Rhine waterway and answer the questions that follow :
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- Transport and Communication
Study the following table carefully and answer the questions that follow :
India – Trends of Urbanisation
Year Number of Towns/UAs Urban Population (in Thousands) % of Total Population Decennial Growth (%) 1931 2,072 33,456.0 11.99 19.12 1941 2,250 44,153.3 13.86 31.97 1951 2,843 62,443.7 17.29 41.42 1961 2,365 78,936.6 17.97 26.41 1971 2,590 1,09,114 19.91 38.23 1981 3,378 1,59,463 23.34 46.14 1991 4,689 2,17,611 25.71 36.47 2001 5,161 2,85,355 27.78 31.13 - CBSE CLASS XII - 2025
- Population Geography
- “In India, water resources are getting polluted with industrial effluents, domestic waste, and insecticides used in agriculture.” Evaluate the statement.
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- Water Resources
- “India’s water demand is highly dominated by irrigation needs.” Evaluate the statement.
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- Water Resources
Notes on Principles of Inheritance and Variation
Concepts Used:
Chromosomal Theory of Inheritance
Chromosomal theory: Linkage and Genetic Recombination
If two genes were present on the same chromosome, the chances of getting a parental combination were much higher in the next generation in comparison to the non-parental combination. This physical association of genes was termed ‘linkage’. The description of the non-parental gene combinations in a dihybrid cross is termed ‘genetic recombination'. After the discovery of linked genes, the frequency of linked genes also influenced the appearance of traits in the next generation.
Observations of Chromosomal Theory of Inheritance:
- During the cell division-meiosis process, the pairs of homologous chromosomes move as discrete structures, which are independent of other pairs of chromosomes.
- From each homologous pair, there is a random distribution of chromosomes into the pre-gametes.
- Each parent synthesizes gametes, which add up to only half of their chromosomal complement.
- Even though female (egg) and male (sperm) gametes differ in morphology and size, they have the same number of chromosomes, submitting equal genetic contributions from each parent.
- The gametic chromosomes fuse during the process of fertilization to produce offspring with the same number of a chromosome as their parents.
Read More: Chromosomal Theory of Inheritance