To determine which of the options provided represents a homozygous dominant allele, let's first understand some key genetic terminology:
1. Allele: A variant form of a gene. Different alleles can result in different traits.
2. Homozygous: This means having two identical alleles for a particular gene. There are two types:
- Homozygous Dominant: This means having two dominant alleles (e.g., RR).
- Homozygous Recessive: This means having two recessive alleles (e.g., rr).
3. Heterozygous: This means having one dominant and one recessive allele for a particular gene (e.g., Rr).
Now, let's evaluate each option given in the problem:
1. Option 1: wr
- "wr" represents a heterozygous allelism with one dominant (W) and one recessive (r) allele, or it may be interpreted as two different alleles depending on the context.
- This is not a homozygous dominant allele.
2. Option 2: Rr
- "Rr" represents a heterozygous allele with one dominant (R) and one recessive (r) allele.
- This is not a homozygous dominant allele.
3. Option 3: RR
- "RR" represents a homozygous dominant allele with two identical dominant alleles (R).
- This fits the definition of a homozygous dominant allele.
4. Option 4: Rw
- "Rw" potentially represents a heterozygous allele, assuming "R" is dominant and "w" is a recessive allele, or it may be interpreted as two different alleles.
- This is not a homozygous dominant allele.
Therefore, the correct answer is option 3, which corresponds to "RR". This is the example of a homozygous dominant allele.
Answer: 3 (RR)
