Overview
This lecture explains the concepts of genotype and phenotype, including how alleles are inherited and expressed in organisms.
Basic Genetics Concepts
- Each organism inherits one allele (gene variant) from each parent for every gene.
- The combination of alleles an organism has is called its genotype.
- If both alleles are the same, the genotype is homozygous.
- If the two alleles are different, the genotype is heterozygous.
- Dominant alleles mask the presence of recessive alleles in heterozygous genotypes.
- A recessive trait is only expressed if both alleles are recessive (homozygous recessive).
- Genotypes are recorded using two letters: uppercase for dominant (e.g., D), lowercase for recessive (e.g., d).
Genotype to Phenotype
- The genotype determines the phenotype, which is the organism's observable traits or appearance.
- Common genotype examples:
- Homozygous dominant: XX
- Homozygous recessive: xx
- Heterozygous: Xx
Key Terms & Definitions
- Genotype — the genetic makeup of an organism (allele combination).
- Phenotype — the observable physical traits of an organism.
- Allele — a version of a gene inherited from each parent.
- Homozygous — having two identical alleles for a gene.
- Heterozygous — having two different alleles for a gene.
- Dominant allele — an allele that expresses its effect even when paired with a different allele.
- Recessive allele — an allele that is masked by a dominant allele and only expressed if both alleles are recessive.
Action Items / Next Steps
- Use the provided information to identify genotypes and phenotypes for given examples or worksheet questions.