rint, while RNA acts as a messenger and regulator.

Protein Synthesis: The Central Dogma

Transcription and Translation

The Central Dogma of Molecular Biology describes the flow of genetic information: DNA is transcribed into RNA, which is then translated into protein. Proteins carry out most cellular functions.

• Transcription: DNA is used as a template to synthesize messenger RNA (mRNA).

• Translation: Ribosomes read mRNA codons and assemble amino acids into a protein.

• Codon: Sequence of three RNA bases specifying an amino acid.

Equation:

Chromosomes and Cell Division

Mitosis vs. Meiosis

Cell division is essential for growth, repair, and reproduction. Mitosis produces identical cells, while meiosis generates gametes with genetic variation.

• Mitosis: Produces two identical diploid cells.

• Meiosis: Produces four haploid gametes; increases genetic diversity via recombination.

Equation:

Mendelian and Non-Mendelian Inheritance

Alleles, Genotype, and Phenotype

Genes exist in different forms called alleles. Each individual inherits two alleles per gene, one from each parent. The combination determines genotype and phenotype.

• Allele: Variant of a gene.

• Homozygous: Two identical alleles (e.g., AA or aa).

• Heterozygous: Two different alleles (e.g., Aa).

• Genotype: Genetic makeup (allele pair).

• Phenotype: Observable trait.

Dominant vs. Recessive Alleles

• Example: Purple flower (B) is dominant to white (b). Genotypes BB or Bb = purple; bb = white.

Punnett Squares and Probability

Punnett squares are used to predict offspring genotypes and phenotypes from parental crosses.

• Monohybrid Cross: Bb × Bb yields 1 BB : 2 Bb : 1 bb (genotype), 3 purple : 1 white (phenotype).

• Dihybrid Cross: AaBb × AaBb yields 9:3:3:1 ratio for two traits.

Pedigrees

Pedigree charts track inheritance patterns in families. Squares represent males, circles represent females, and shaded symbols indicate affected individuals. Analysis reveals dominant, recessive, autosomal, or sex-linked traits.

• Autosomal recessive: Unaffected parents can have affected children (carriers).

• Dominant: Trait appears in every generation.

Non-Mendelian Genetics

Patterns Beyond Mendel

Some traits do not follow simple dominant/recessive rules. These include incomplete dominance, codominance, and sex-linked inheritance.

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., pink flowers).

• Codominance: Both alleles are fully expressed (e.g., blood type AB).

• Sex-linked: Traits carried on sex chromosomes (e.g., colorblindness).

• Mitochondrial inheritance: Traits passed via mitochondrial DNA.

Genetic Variation and Biotechnology

Sources of Variation

Genetic variation arises from mutations, recombination during meiosis, and independent assortment. Variation is essential for evolution and adaptation.

• Mutation: Change in DNA sequence; can be neutral, beneficial, or harmful.

• Recombination: Exchange of genetic material during meiosis.

• Biotechnology: Modern applications include genetic testing, GMOs, and CRISPR gene editing.

Key Vocabulary

• Genetics

• Gene

• Allele

• Chromosome

• Genome

• Homozygous

• Heterozygous

• Genotype

• Phenotype

• Dominant

• Recessive

• Mitosis

• Meiosis

• Homologous chromosomes

• Mutation

Common Misconceptions

• Dominant means common: Not always; dominance refers to masking, not frequency.

• One parent gives all traits: Both parents contribute alleles.

• Punnett squares predict actual individuals: They show probabilities, not certainties.

• Mutation only harmful: Mutations can be neutral or beneficial.

Example Problems

• Blood Type Cross: IAi × IBi yields IAIB (AB), IAi (A), IBi (B), ii (O); phenotypes: 25% each.

• Pedigree Analysis: Two unaffected parents have an affected child; suggests recessive trait.

Historical Milestones in Genetics

Summary

Genetics is central to understanding biological inheritance, cell division, and variation. Key concepts include DNA structure, gene function, chromosome organization, mitosis and meiosis, Mendelian and non-Mendelian inheritance, and modern biotechnology. Mastery of these topics provides a foundation for advanced study in biology and related fields.