Specimen Prep - Principles of Inheritance and Variation

Specimen Prep Guide: Principles of Inheritance and Variation

Key Concepts (Recall & Understanding)

• Mendel's Laws: Understand the Law of Dominance, Law of Segregation, and Law of Independent Assortment.
• Deviations from Mendelism: Know about incomplete dominance, co-dominance, multiple alleles, and pleiotropy.
• Chromosomal Theory: Understand the contribution of Sutton and Boveri.
• Sex Determination: Know the mechanisms of sex determination in humans, birds, and honeybees.
• Genetic Disorders: Differentiate between Mendelian disorders (e.g., haemophilia, sickle-cell anemia) and chromosomal disorders (e.g., Down's syndrome, Turner's syndrome).

Application Corner

• Problem Type: Solving monohybrid, dihybrid, and test cross problems. Analyzing pedigree charts to determine the pattern of inheritance.
• Example: A man with blood group A marries a woman with blood group B. Their first child has blood group O. What is the probability of their next child having blood group AB? (Answer: 25%).

Analytical Thinking

• Scenario: A pedigree chart shows a trait appearing in every generation and affecting both males and females equally. What is the likely mode of inheritance?
• Analysis: Autosomal dominant.
• Diagram Interpretation: Be able to interpret a karyotype to identify chromosomal abnormalities.

Key Experiment

• T.H. Morgan's work on Drosophila melanogaster: His experiments on fruit flies established the chromosomal theory of inheritance and the concept of linkage and recombination.

Assertion-Reason Practice

1. Assertion: The law of dominance is not universally applicable. Reason: It is not applicable in cases of incomplete dominance and co-dominance.

   • (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

2. Assertion: A male human can never be a carrier of haemophilia. Reason: Haemophilia is a sex-linked recessive disorder, and males have only one X chromosome.

   • (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

HOTS (Higher-Order Thinking Skills) Question

• A tall pea plant with round seeds (TtRr) is crossed with a dwarf pea plant with wrinkled seeds (ttrr). What percentage of the progeny will be tall with wrinkled seeds?
  • Answer: 25%. The cross will produce four phenotypes (tall-round, tall-wrinkled, dwarf-round, dwarf-wrinkled) in the ratio 1:1:1:1.