DNA and Genetics Lecture

Key Terms and Concepts

Alleles

• Definition: Different versions of the same gene.
• We have two alleles for each gene (one from each parent).
• Homozygous: Two identical alleles for a gene.
• Heterozygous: Two different alleles for a gene.

Dominant and Recessive Alleles

• Dominant allele: The allele that gets expressed in the phenotype when present.
• Recessive allele: The allele that is not expressed in the phenotype unless it is homozygous.
• Example: For a mouse with fur color alleles, if purple (dominant) and green (recessive) alleles are present, the mouse will have purple fur.

Genotype and Phenotype

• Genotype: The entire collection of alleles an organism has.
  • Example: Heterozygous (purple/green), Homozygous dominant (purple/purple), Homozygous recessive (green/green).
• Phenotype: The observable characteristics determined by the genotype.
  • Example: Both heterozygous (purple/green) and homozygous dominant (purple/purple) display purple fur, so they have the same phenotype but different genotypes.

Application and Examples

• Traits like fur color in mice can be determined by single genes, while others like height involve multiple genes.
• Single-gene traits: Fur color in mice, red-green color blindness in humans.
• Multi-gene traits: Height in humans.

Next Steps

• Preview of next lecture: Genetic diagrams.