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Q1:
Mention the advantages of selecting pea plant for experiment by Mendel.
Solution :
1. Biological and Physical Attributes of Pisum sativum
Gregor Johann Mendel’s selection of the garden pea (Pisum sativum) was a strategic decision based on both biological convenience and statistical advantages. The plant offered several distinct traits that made it the ideal model organism for observing patterns of inheritance.
2. Key Advantages: An Analytical Breakdown
- Distinctive and Contrasting Characters: The pea plant exhibits several sharply defined, non-blending traits. Mendel focused on seven pairs of contrasting characters (e.g., Tall vs. Dwarf, Violet vs. White flowers). This binary nature [per Mendel’s Law of Segregation] allowed for clear observation of dominance and recessiveness.
- Short Life Cycle: Pisum sativum is an annual plant with a short life span. This allowed Mendel to study multiple generations (up to the $F_2$ and $F_3$ generations) within a single growing season, providing a large data set in a relatively short timeframe.
- High Productivity and Large Sample Size: Pea plants produce a large number of seeds per pod. A larger sample size statistically minimizes the margin of error, allowing Mendel to apply probability and ratio-based analysis (e.g., the $3:1$ phenotypic ratio) to his findings.
- Ease of Controlled Cross-Pollination: The flower structure of the pea plant is hermaphroditic (bisexual), containing both male and female reproductive organs. However, the structure is designed such that self-pollination is natural, allowing for the creation of "pure-breeding" (homozygous) lines. Furthermore, the large size of the flowers made manual emasculation and artificial cross-pollination technically straightforward.
3. Comparative Table of Traits Observed
| Character | Dominant Trait | Recessive Trait |
|---|---|---|
| Stem Height | Tall | Dwarf |
| Flower Color | Violet | White |
| Seed Shape | Round | Wrinkled |
| Seed Color | Yellow | Green |
4. Visual Representation of Mendel's Monohybrid Cross
5. Statistical Justification
By using self-pollinating organisms, Mendel ensured that he started with homozygous lines ($AA$ or $aa$). Through the deliberate crossing of these lines, he could track the transmission of alleles across generations. [By the Law of Independent Assortment], he was able to conclude that traits are governed by particulate units (genes), a fundamental shift from the then-prevalent "blending inheritance" hypothesis.
Final Solution: The selection of Pisum sativum was advantageous due to its short generation time, high seed yield, ease of manual cross-pollination, and the presence of seven distinct, clearly contrasting pairs of inherited traits which facilitated rigorous statistical analysis.
More Questions from Class 12 Biology Principles of Inheritance and Variation EXERCISES
- 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.
- 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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