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Q9:
Briefly mention the contribution of T.H. Morgan in genetics.
Solution :
1. Foundation of Chromosomal Theory of Inheritance
Thomas Hunt Morgan (1866–1945) utilized the fruit fly, Drosophila melanogaster, as a model organism to provide experimental evidence for the chromosomal theory of inheritance [Per the Sutton-Boveri Chromosomal Theory]. His work moved genetics from abstract mathematical ratios (Mendelian) to physical entities located on chromosomes.
2. Key Experimental Contributions
- Linkage: Morgan observed that genes located on the same chromosome do not always assort independently. He defined linkage as the physical association of genes on a chromosome, which results in the parental combination of alleles being inherited together more frequently than expected by independent assortment [Per the Principle of Genetic Linkage].
- Recombination: He identified that linkage is not absolute. During meiosis, genetic material can be exchanged between homologous chromosomes via crossing over, leading to non-parental (recombinant) gene combinations [Per the Crossing-Over Mechanism].
- Sex-Linked Inheritance: Morgan discovered the phenomenon of X-linked inheritance by observing white-eyed male Drosophila. He proved that the gene for eye color is located specifically on the X-chromosome, establishing that inheritance patterns are influenced by sex-determining chromosomes [Per the Law of Segregation in Sex Chromosomes].
3. Chromosomal Mapping
Morgan’s student, Alfred Sturtevant, used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between them. This paved the way for the construction of Genetic Maps [Per the Map Unit (centimorgan) convention].
4. Summary Table of Morgan’s Discoveries
| Contribution | Biological Significance |
|---|---|
| Linkage | Genes on the same chromosome tend to be inherited together. |
| Crossing Over | Generation of genetic variation through recombination. |
| Sex-Linkage | Confirmed that specific genes are physically mapped to sex chromosomes. |
5. Visual Representation of Linkage vs. Crossing Over
Final Solution: T.H. Morgan is celebrated as the "Father of Experimental Genetics" for his discovery of linkage, sex-linkage, and crossing-over in Drosophila melanogaster, which provided the physical basis for genetic inheritance and the foundation for chromosomal mapping.
More Questions from Class 12 Biology Principles of Inheritance and Variation EXERCISES
- Q1: Mention the advantages of selecting pea plant for experiment by Mendel.
- Q1: Mention the advantages of selecting pea plant for experiment by Mendel.
- Q2(a): Differentiate between the following – (a) Dominance and Recessive
- Q2(a): Differentiate between the following – (a) Dominance and Recessive
- Q2(b): Differentiate between the following – (b) Homozygous and Heterozygous
- Q2(b): Differentiate between the following – (b) Homozygous and Heterozygous
- Q2(c): Differentiate between the following – (c) Monohybrid and Dihybrid.
- Q2(c): Differentiate between the following – (c) Monohybrid and Dihybrid.
- Q3: A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?
- Q3: A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?
- Q4: Explain the Law of Dominance using a monohybrid cross.
- Q4: Explain the Law of Dominance using a monohybrid cross.
- Q5: Define and design a test-cross.
- Q5: Define and design a test-cross.
- Q6: Using a Punnett Square, workout the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.
- Q6: Using a Punnett Square, workout the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.
- Q7(a): When a cross in made between tall plant with yellow seeds (\(TtYy\)) and tall plant with green seed (\(Ttyy\)), what proportions of phenotype in the offspring could be expected to be (a) tall and green.
- Q7(a): When a cross in made between tall plant with yellow seeds ((TtYy)) and tall plant with green seed ((Ttyy)), what proportions of phenotype in the offspring could be expected to be (a) tall and green.
- Q7(b): When a cross in made between tall plant with yellow seeds (\(TtYy\)) and tall plant with green seed (\(Ttyy\)), what proportions of phenotype in the offspring could be expected to be (b) dwarf and green.
- Q7(b): When a cross in made between tall plant with yellow seeds ((TtYy)) and tall plant with green seed ((Ttyy)), what proportions of phenotype in the offspring could be expected to be (b) dwarf and green.
- Q8: Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in \(F_{1}\) generation for a dibybrid cross?
- Q8: Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in (F_{1}) generation for a dibybrid cross?
- Q9: Briefly mention the contribution of T.H. Morgan in genetics.
- Q10: What is pedigree analysis? Suggest how such an analysis, can be useful.
- Q10: What is pedigree analysis? Suggest how such an analysis, can be useful.
- Q11: How is sex determined in human beings?
- Q11: How is sex determined in human beings?
- Q12: A child has blood group O. If the father has blood group A and mother blood group B, work out the genotypes of the parents and the possible genotypes of the other offsprings.
- Q12: A child has blood group O. If the father has blood group A and mother blood group B, work out the genotypes of the parents and the possible genotypes of the other offsprings.
- Q13(a): Explain the following terms with example (a) Co-dominance
- Q13(a): Explain the following terms with example (a) Co-dominance
- Q13(b): Explain the following terms with example (b) Incomplete dominance
- Q13(b): Explain the following terms with example (b) Incomplete dominance
- Q14: What is point mutation? Give one example.
- Q14: What is point mutation? Give one example.
- Q15: Who had proposed the chromosomal theory of the inheritance?
- Q15: Who had proposed the chromosomal theory of the inheritance?
- Q16: Mention any two autosomal genetic disorders with their symptoms.
- Q16: Mention any two autosomal genetic disorders with their symptoms.
CBSE Solutions for Class 12 Biology Principles of Inheritance and Variation
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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