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Q2(c):
Differentiate between the following –
(c) Monohybrid and Dihybrid.
Solution :
Definition and Theoretical Framework
The distinction between a monohybrid and a dihybrid cross is rooted in the number of contrasting traits under investigation during a hybridization experiment, governed by Mendel’s Laws of Inheritance.
| Feature | Monohybrid Cross | Dihybrid Cross |
|---|---|---|
| Definition | A cross considering a single pair of contrasting alleles. | A cross considering two pairs of contrasting alleles. |
| Governing Law | Law of Dominance and Law of Segregation. | Law of Independent Assortment. |
| Genotypic Ratio ($F_2$) | $1:2:1$ | $1:2:1:2:4:2:1:2:1$ |
| Phenotypic Ratio ($F_2$) | $3:1$ | $9:3:3:1$ |
Step 1: The Monohybrid Mechanism
A monohybrid cross involves tracking one character (e.g., plant height). [Per the Law of Segregation, alleles for a trait separate during gamete formation so that each gamete carries only one allele].
Example: $TT \times tt \rightarrow F_1: Tt \rightarrow F_2: 3 \text{ Tall} : 1 \text{ Dwarf}$.
Step 2: The Dihybrid Mechanism
A dihybrid cross involves tracking two characters (e.g., seed color and seed shape). [Per the Law of Independent Assortment, the segregation of one pair of alleles is independent of the segregation of another pair of alleles].
Example: $YYRR \times yyrr \rightarrow F_1: YyRr \rightarrow F_2: 9:3:3:1$ phenotypic ratio.
Step 3: Visual Representation of Segregation Patterns
Analytical Summary
The Monohybrid cross is used to establish the concept of dominance and the purity of gametes. The Dihybrid cross provides the proof for the independent inheritance of distinct traits, resulting in a broader genetic recombination in the $F_2$ generation.
Final Solution: A monohybrid cross analyzes the inheritance pattern of one trait governed by the Law of Segregation, yielding a $3:1$ phenotype ratio, whereas a dihybrid cross analyzes two traits governed by the Law of Independent Assortment, yielding a $9:3:3:1$ phenotype ratio.
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.
- 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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