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Q2(c):
Differentiate between the following –
(c) Monohybrid and Dihybrid.
Solution :
Definition and Theoretical Foundation
The distinction between a monohybrid and a dihybrid cross is rooted in the number of contrasting traits under observation during a hybridization experiment, governed by Mendel’s Laws of Inheritance. [Per the Law of Segregation and the Law of Independent Assortment].
| Feature | Monohybrid Cross | Dihybrid Cross |
|---|---|---|
| Definition | Cross involving a single pair of contrasting characters. | Cross involving two pairs of contrasting characters. |
| Governing Law | Law of Segregation (Mendel's First Law). | Law of Independent Assortment (Mendel's Second Law). |
| Typical Genotypic Ratio ($F_2$) | $1:2:1$ | $(1:2:1)^2 = 1:2:1:2:4:2:1:2:1$ |
| Typical Phenotypic Ratio ($F_2$) | $3:1$ | $9:3:3:1$ |
Step 1: Analyzing the Monohybrid Cross
In a monohybrid cross, we track the inheritance of one trait (e.g., stem height). Parents: $TT$ (Tall) $\times$ $tt$ (Dwarf). The $F_1$ generation is $Tt$. Selfing the $F_1$ generation results in $F_2$ gametes following a $1:2:1$ genotypic distribution.
Step 2: Analyzing the Dihybrid Cross
In a dihybrid cross, two traits are studied simultaneously (e.g., seed shape and seed color). Parents: $RRYY$ (Round Yellow) $\times$ $rryy$ (Wrinkled Green). The $F_1$ generation is $RrYy$. The $F_2$ generation exhibits 16 possible combinations, resulting in the $9:3:3:1$ phenotypic ratio [By Independent Assortment of alleles on non-homologous chromosomes].
Step 3: Visual Representation
Conclusion on Biological Variation
The monohybrid cross demonstrates the purity of gametes and dominance. Conversely, the dihybrid cross demonstrates that factors for different traits segregate and assort independently, thereby increasing genetic variation within a population [Per the Law of Independent Assortment].
Final Solution: A monohybrid cross involves the inheritance pattern of one distinct trait (ratio $3:1$ phenotypic), while a dihybrid cross involves the simultaneous inheritance of two traits (ratio $9:3:3:1$ phenotypic), governed by Mendel’s Second Law of Independent Assortment.
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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