1. Genotype
* Homozygous Dominant: This refers to an individual having two identical dominant alleles for a specific trait. Represented by two capital letters, for example, AA.
* Heterozygous Recessive: This refers to an individual having one dominant allele and one recessive allele for a specific trait. Represented by one capital letter and one lowercase letter, for example, Aa.
2. Phenotype
* Homozygous Dominant: The individual expresses the dominant trait. For example, if "A" represents the allele for brown eyes, then an individual with AA will have brown eyes.
* Heterozygous Recessive: The individual also expresses the dominant trait. This is because the dominant allele masks the recessive allele. For example, if "a" represents the allele for blue eyes, an individual with Aa will still have brown eyes.
3. Offspring
* Homozygous Dominant: An individual with AA will always pass on the dominant allele to their offspring.
* Heterozygous Recessive: An individual with Aa has a 50% chance of passing on the dominant allele and a 50% chance of passing on the recessive allele to their offspring.
Example:
Let's use the example of eye color:
* Brown Eyes: The dominant allele for brown eyes is "B".
* Blue Eyes: The recessive allele for blue eyes is "b".
* Homozygous Dominant: An individual with BB will have brown eyes.
* Heterozygous Recessive: An individual with Bb will also have brown eyes.
Key Differences:
The key difference lies in the genotype. Homozygous dominant individuals have two copies of the dominant allele, while heterozygous recessive individuals have one copy of each, dominant and recessive. This difference, however, does not affect the phenotype in most cases, as the dominant allele masks the recessive one.
In Summary:
| Feature | Homozygous Dominant | Heterozygous Recessive |
|---|---|---|
| Genotype | AA (two dominant alleles) | Aa (one dominant, one recessive) |
| Phenotype | Dominant trait expressed | Dominant trait expressed |
| Offspring | Always passes on dominant allele | 50% chance of passing on dominant allele, 50% chance of passing on recessive allele |
