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Q16:
Mention any two autosomal genetic disorders with their symptoms.
Solution :
1. Sickle Cell Anemia: An Autosomal Recessive Disorder
Sickle cell anemia is a hemoglobinopathy caused by a point mutation in the $\beta$-globin chain of the hemoglobin molecule. It is inherited in an autosomal recessive pattern [Per Mendelian Laws of Inheritance].
Mechanism of Action:
- The mutation involves the substitution of Glutamic acid ($Glu$) by Valine ($Val$) at the sixth position of the $\beta$-globin chain.
- This is caused by a single base substitution ($GAG \rightarrow GUG$) at the sixth codon of the $\beta$-globin gene ($HBB$).
- Under conditions of low oxygen tension, the mutant hemoglobin undergoes polymerization, causing the erythrocyte to lose its biconcave shape and assume a sickle-like structure [Per Molecular Basis of Inheritance].
Clinical Symptoms:
- Chronic Anemia: The sickle-shaped cells are fragile and undergo rapid hemolysis, leading to a shortened lifespan ($10-20$ days compared to the normal $120$ days).
- Vaso-occlusive Crises: Sickled cells block micro-capillaries, leading to severe localized pain, organ damage (particularly in the spleen), and episodic fever.
2. Phenylketonuria (PKU): An Autosomal Recessive Metabolic Disorder
Phenylketonuria is an inborn error of metabolism resulting from a mutation in the gene encoding the enzyme phenylalanine hydroxylase ($PAH$), located on chromosome $12$ [Per Human Genetics Mapping].
Mechanism of Action:
- The defective $PAH$ enzyme fails to convert the amino acid Phenylalanine into Tyrosine.
- This results in the accumulation of Phenylalanine in the blood and body tissues.
- Excess Phenylalanine is subsequently converted into phenylpyruvic acid and other derivatives, which are excreted in the urine due to poor kidney reabsorption.
Clinical Symptoms:
- Neurological Impairment: Accumulation of Phenylalanine derivatives in the brain leads to severe mental retardation.
- Physiological Manifestations: Reduced skin and hair pigmentation occurs because of the metabolic diversion away from melanin synthesis [Per Biochemical Pathway Logic].
Summary Comparison
| Disorder | Chromosomal Location | Primary Pathophysiology |
|---|---|---|
| Sickle Cell Anemia | Chromosome $11$ | Hemoglobin polymerization |
| Phenylketonuria | Chromosome $12$ | Enzyme ($PAH$) deficiency |
Final Solution: The two autosomal genetic disorders are Sickle Cell Anemia (characterized by hemolytic anemia and vaso-occlusion due to abnormal hemoglobin) and Phenylketonuria (characterized by mental retardation and reduced pigmentation due to phenylalanine hydroxylase deficiency).
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(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.
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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