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Q10:
What is pedigree analysis? Suggest how such an analysis, can be useful.
Solution :
Definition: Pedigree Analysis
Pedigree analysis is the study of the inheritance of specific traits or genetic disorders over several generations within a family. It involves the construction and systematic examination of a pedigree chart (or family tree), which utilizes standardized symbols to represent individuals (males as squares, females as circles) and their ancestral lineages [Per Mendelian Genetics and human heredity principles].
Standardized Pedigree Symbols
Step 1: Establishing the Utility of Pedigree Analysis
Pedigree analysis is a crucial tool in human genetics because controlled crosses, which are possible in model organisms like Drosophila melanogaster, cannot be performed on humans for ethical and practical reasons. The analysis is useful for the following reasons:
- Determining Mode of Inheritance: It helps identify whether a trait is governed by a dominant or recessive allele. Furthermore, it clarifies if the trait is located on an autosome or a sex chromosome ($X$ or $Y$).
- Genetic Counseling: By analyzing the family history, geneticists can calculate the probability of a future offspring inheriting a specific genetic disorder [Per Probability Theory in Genetics].
- Tracing Genetic Disorders: It facilitates the tracing of hereditary diseases such as haemophilia, cystic fibrosis, sickle-cell anaemia, and phenylketonuria through multiple generations.
- Identifying Carriers: It allows for the identification of phenotypically normal individuals who carry a recessive allele for a disorder, which is essential for family planning.
Step 2: Analytical Framework for Inheritance Patterns
| Pattern | Key Characteristic |
|---|---|
| Autosomal Dominant | Does not skip generations; affected individuals usually have an affected parent. |
| Autosomal Recessive | Often skips generations; parents are typically phenotypically normal carriers. |
| X-linked Recessive | More males affected than females; trait is passed from carrier mother to son (criss-cross inheritance). |
Step 3: Logical Application
To perform an analysis, the following logical operations are conducted:
- Data Collection: Recording phenotypes of individuals across at least three generations.
- Pattern Recognition: Assessing if the trait appears in every generation (suggesting dominance) or if there is a gender bias in inheritance (suggesting sex-linkage).
- Genotypic Deduction: Using the phenotypes of parents and progeny to assign genotypes ($AA, Aa, aa$) based on the Law of Segregation [Per Mendel's First Law].
Final Solution: Pedigree analysis is the retrospective study of family history to trace the inheritance of traits. It is an indispensable tool in medical genetics used to determine the mode of transmission of genetic disorders, identify carriers within a family, and provide accurate genetic counseling for informed reproductive decision-making.
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.
- 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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