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Q13(a):
Explain the following terms with example
(a) Co-dominance
Solution :
1. Definition and Theoretical Foundation
Co-dominance is a phenomenon of inheritance where both alleles of a gene pair express themselves equally and simultaneously in the $F_1$ hybrid. Unlike incomplete dominance, where an intermediate phenotype is produced, co-dominance results in both parental traits appearing distinctly in the heterozygous offspring. [Per Mendelian deviation principles, this occurs when neither allele is dominant or recessive to the other.]
2. Genetic Mechanism
In a heterozygous genotype $Aa$, if the gene is co-dominant, the product of allele $A$ and the product of allele $a$ are both fully functional and observable in the phenotype. This implies that the heterozygote displays a mosaic or mixed phenotype rather than a blend.
3. Exemplar: The ABO Blood Grouping System
The human ABO blood group system is governed by the gene $I$ (isoagglutinogen). This gene exists in three allelic forms: $I^A$, $I^B$, and $i$.
- The alleles $I^A$ and $I^B$ produce different types of sugar polymers on the surface of red blood cells.
- The allele $i$ does not produce any sugar polymer.
- When an individual possesses the genotype $I^A I^B$, both $I^A$ and $I^B$ are expressed simultaneously.
4. Visual Representation: Co-dominance in Blood Phenotype
5. Comparative Analysis
| Feature | Co-dominance |
|---|---|
| Expression | Both alleles expressed fully. |
| $F_1$ Phenotype | Combination of both parental traits. |
| Example | $AB$ Blood group; Coat color in Shorthorn cattle. |
6. Conclusion
In the case of $I^A I^B$ individuals, the presence of both $A$ and $B$ antigens on the surface of the erythrocytes serves as direct biological evidence that neither allele masks the other, thus confirming the state of co-dominance. [Ref: $I^A = I^B > i$].
Final Solution: Co-dominance is the inheritance pattern where both alleles in a heterozygote are fully expressed in the phenotype, exemplified by the $I^A I^B$ genotype in humans, resulting in the AB blood type.
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.
- 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(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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