Genetics & Breeding
Alleles, Homozygosity & Heterozygosity
Diploid loci can carry two copies of an allele that are the same or different. Homozygosity and heterozygosity are locus-specific concepts that help explain segregation, uniformity, and the persistence of variation across generations.
Key concepts
- Homozygous and heterozygous describe allele state at a locus, not the whole plant in one word
- Dominance affects phenotype but does not erase the hidden allele
- Many important traits are influenced by multiple loci
- Population history changes expected heterozygosity
What to measure or observe
- Track parentage and generation
- Use trait segregation as evidence rather than assuming genotype from appearance
- Separate single-gene examples from polygenic traits
- Use molecular data when genotype at a specific locus actually matters
Common mistakes
- Calling an entire line homozygous from one visible trait
- Assuming dominant means more common or better
- Applying simple Mendelian ratios to every quantitative trait
- Ignoring linkage and population size
Visuals this lesson still needs
- Allele-pair diagrams
- Homozygous versus heterozygous examples
- Dominance phenotype table
- Single-gene versus polygenic comparison