Overview
This lecture explains the difference between genotype and phenotype, and introduces basic genetic terms such as alleles, genes, and dominance.
Genotype vs. Phenotype
- Genotype is the genetic code present in your cells.
- Phenotype is the physical expression or traits resulting from the genotype.
- Your phenotype depends on the genotype stored in your chromosomes.
Genes, Chromosomes, and Alleles
- Genetic information is found on chromosomes in sections called genes.
- A gene is a DNA segment that codes for a specific trait.
- Different forms of the same gene are called alleles.
- You inherit genes (and thus alleles) from both your mother and father.
Types of Genotypes
- Three genotype types: homozygous dominant, homozygous recessive, and heterozygous.
- Homozygous means having two identical alleles (dominant or recessive).
- Heterozygous means having two different alleles for a trait.
Dominant and Recessive Alleles
- A dominant allele masks the effect of a recessive allele in heterozygotes.
- A recessive trait appears only if both alleles are recessive.
Examples of Phenotypes
- Physical characteristics, like a dog's round nose or a cat's black hair, are phenotypes.
Key Terms & Definitions
- Genotype — the genetic code of an organism.
- Phenotype — the observable physical traits of an organism.
- Gene — a DNA segment coding for a trait.
- Allele — different forms of the same gene.
- Homozygous — having two identical alleles for a trait.
- Heterozygous — having two different alleles for a trait.
- Dominant Allele — an allele that masks the effect of a recessive allele.
- Recessive Allele — an allele whose effect is masked by a dominant allele.
Action Items / Next Steps
- Review your notes on genotypes, phenotypes, and alleles.
- Be able to classify examples as genotype or phenotype.
- Understand the difference between dominant and recessive alleles.