Lecture on Genes, Alleles, Genotypes, and Phenotypes

Key Concepts

• Genes: Sections of DNA located on chromosomes that code for RNA, which is then translated into proteins.
• Alleles: Different versions of a gene found at the same locus on homologous chromosomes.
• Genotypes: The genetic constitution of an individual, represented by the alleles present.
• Phenotypes: Observable traits or characteristics of an organism determined by its genotype.

Genetic Basics

• Diploid Individual: Has two copies of each type of chromosome, one from each parent.
• Chromosome: A long DNA molecule containing many genes.
• Central Dogma: DNA is transcribed into RNA, which is translated into protein, determining phenotypes.

Phenotypes

• Observable traits such as pea color, dog coat color, or human height.
• Determined by the proteins that are produced from the gene sequences.

Alleles

• Example: Mice coat colors (Black and White).
• B1 and B2 alleles represent different versions of a coat color gene.
• Difference between alleles is due to variations in DNA sequence.

Genotypes

• Homozygous: Both alleles are the same (e.g., B1/B1 or B2/B2).
• Heterozygous: Different alleles present (e.g., B1/B2).
  • Genotype notation: B1/B1, B2/B2, B1/B2.

Phenotypes and Dominance

• Homozygous Phenotype: Direct expression based on allele (e.g., B1/B1 = Black, B2/B2 = White).
• Heterozygous Phenotype: Determined by the dominant allele.
  • If phenotype is like B1, B1 is dominant, B2 is recessive.
  • Dominance assessed by phenotype of heterozygous individuals.

Summary

• Genes: DNA sequences transcribed into RNA and translated into protein.
• Alleles: Variants of genes due to different DNA sequences.
• Homozygous vs. Heterozygous: Same vs. different alleles.
• Dominance: Determined by the phenotype of heterozygous individuals.