Lecture Notes: Inheritance Principles (Chapter 11 Biology)

Introduction

• Topic: Inheritance (Chapter 11, Form 5 Biology)
• Relevance: Understanding principles of inheritance, important for exams like SPM
• Objective: Learn 8 key concepts, no need for memorization, understand terms and you can answer questions

Key Terms

1. Gene (Jin)
   • Composed of A, C, G, T sequences
   • Represented by alphabets in characteristics e.g., T for tall, t for short
2. Allele
   • Alternative form of a gene
   • Represented by capital or small letters e.g., T (dominant), t (recessive)
3. Dominant Allele
   • Represents 'king'
   • Written in capital letters e.g., T
   • One allele is enough to show dominance
4. Recessive Allele
   • Represents 'army'
   • Written in small letters e.g., t
   • Need two alleles to show recessive trait
5. Homozygous Dominant
   • Homo = same, Dominant = king
   • Written as two capital letters e.g., TT, GG
6. Heterozygous
   • Hetero = different
   • One dominant and one recessive allele e.g., Tt
7. Homozygous Recessive
   • Homo = same, Recessive = army
   • Written as two small letters e.g., tt, gg
8. Genotype
   • Genetic make-up represented by alleles e.g., TT, Tt, tt
9. Phenotype
   • Physical appearance of an organism e.g., tall, short

Examples

1. Genotype and Phenotype Examples
   • RR (Red), Rr (Red), rr (White)
   • Dominant trait (red) shown even with one dominant allele
   • Recessive trait (white) shown only with two recessive alleles

Mendel's Laws

1. First Law: Law of Segregation

   • Separation of alleles during gamete formation (anaphase)
   • Focuses on one characteristic (monohybrid)

2. Second Law: Independent Assortment

   • Genes for different traits can segregate independently during the formation of gametes
   • Focuses on two characteristics (dihybrid)
   • Affects genetic variation

Diagram Drawing: Monohybrid Cross

1. Steps
   • Determine the genotype of the parents
   • Represent the gametes
   • Use Punnett square for fertilization
   • Derive F1 generation genotype and phenotype
   • Calculate genotypic and phenotypic ratios

Diagram Drawing: Dihybrid Cross

1. Steps
   • Similar to monohybrid cross but consider two traits
   • Identify parental genotypes and gametes
   • Use a larger Punnett square (4x4)
   • Determine F1 generation and then cross for F2
   • Calculate ratios (commonly 9:3:3:1)

Common Questions

1. Punnett Squares and Ratios

   • Calculate exact phenotypic ratios
   • Example setups for mice, pea plants illustrating smooth and wrinkled seeds

2. Understanding Dominant vs Recessive

   • Use examples to identify which traits show dominance (requires observing F1 and F2 generations)

Practical Application

1. Schematic Diagrams
   • Essential for exam questions
   • Practice by drawing multiple examples

Conclusion

• Practice: More you practice, better grasp on inheritance principles
• Comment Questions: Obtain feedback or request for specific topics to be covered in future videos
• Key to Success: Understanding core principles of dominants and recessives and use Punnett squares effectively.