Introduction to Genetics - Miss Angus' Biology Class

General Information

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• Check out the Grade 12 playlist for detailed videos on mono-hybrid, dihybrid crosses, and sex-link disorders.

Basics of Genetics

Chromatin Network

• Found inside the cell nucleus.
• Condenses into chromosomes during mitosis and meiosis.

Chromosomes

• Humans have 46 chromosomes.
• Condensed pieces of DNA.
• DNA sections called genes, responsible for coding characteristics.
• Example genes: height, hair color, eye color, blood group.

Genes vs. Alleles

Definitions

• Gene: A characteristic (e.g., eye color, height).
• Allele: A variation of a gene (e.g., blue eyes, brown eyes).

Homologous Chromosomes

• Paired chromosomes with genes carrying the same characteristics but different alleles.
• One chromosome from the mother (maternal), one from the father (paternal).

Passing on Characteristics

• 46 chromosomes in pairs (homologous pairs).
• Each gene has two alleles (one from each parent).
• During meiosis, homologous chromosomes separate, ensuring only one allele is passed on.
• Example: Eye color genes on chromosomes, blue and green alleles.

Dominant and Recessive Alleles

Allele Notation

• Dominant Allele: Represented by a capital letter (B).
• Recessive Allele: Represented by a lowercase letter (b).

Determining Physical Characteristics (Phenotype)

• Homozygous Dominant (BB): Two dominant alleles, phenotype shows dominant trait.
• Heterozygous (Bb): One dominant and one recessive allele, phenotype shows dominant trait.
• Homozygous Recessive (bb): Two recessive alleles, phenotype shows recessive trait.

Example

• Phenotype: Physical appearance (e.g., purple or white flowers).
• Genotype: Genetic makeup/allele combination (e.g., BB, Bb, bb).

Terms Recap

• Chromatin Network: DNA visible during interphase, condenses into chromosomes.
• Chromosomes: Carry DNA, 46 in humans, important for meiosis.
• Genes: Sections of chromosome coding traits (e.g., height, eye color).
• Alleles: Variations of genes (e.g., green or blue eyes).
• Maternal/Paternal Chromosomes: One from mother, one from father.
• Dominant Alleles: Physically expressed with one present.
• Recessive Alleles: Need two to be expressed.
• Homozygous: Same alleles (BB or bb).
• Heterozygous: Different alleles (Bb).

Conclusion

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