Genetics Notes - Cameroon O-Level

1. Introduction to Genetics

Genetics is the study of heredity and variation in organisms.

• Heredity: Transmission of traits from parents to offspring.
• Variation: Differences among individuals.
• Gene: Unit of heredity on a chromosome.
• Genome: Complete set of genes.

2. Chromosomes and Genes

• Chromosomes carry genetic material.
• Humans have 46 chromosomes (23 pairs).
• Types:
  • Autosomes: 22 pairs
  • Sex chromosomes: 1 pair (XX female, XY male)
• Gene locus: position of a gene on a chromosome

Chromosome Diagram

3. Mendelian Genetics

Gregor Mendel's principles of inheritance:

• Law of Segregation: Alleles separate during gamete formation.
• Law of Independent Assortment: Genes for different traits segregate independently.
• Alleles: Dominant (A) or recessive (a).
• Genotype: Genetic makeup (AA, Aa, aa).
• Phenotype: Observable traits (tall, short).

Punnett Square (Monohybrid Cross)

4. Sex Determination & Sex-linked Traits

• XX = female, XY = male
• Sex-linked inheritance involves genes on sex chromosomes
• Example: Hemophilia (X-linked recessive)

Sex-linked Punnett Square

5. Mutations

• Mutation: permanent change in DNA
• Types:
  • Point: substitution, insertion, deletion
  • Chromosomal: duplication, deletion, inversion, translocation
• Effects: harmful, beneficial, or neutral

6. Genetic Disorders

• Caused by mutations or chromosomal abnormalities
• Examples:
  • Down syndrome: trisomy 21
  • Sickle cell anemia: mutation in hemoglobin gene
  • Albinism: recessive allele disorder

7. Biotechnology Applications

• Genetic engineering: modifying organism’s genome
• Applications: crop improvement, medicine (insulin), forensics
• Ethical considerations are important