Understanding the Basics
* Heterozygous: Means an organism has two different alleles for a particular trait (e.g., one dominant allele and one recessive allele).
* Recessive Phenotype: The physical expression of a trait when two copies of the recessive allele are present.
How it Works
1. Parent Genotypes: Both parents are heterozygous, meaning they each carry one dominant allele (let's represent it with "A") and one recessive allele (represented by "a"). Their genotypes are Aa.
2. Punnett Square: A Punnett square helps visualize the possible combinations of alleles in the offspring:
```
A a
A AA Aa
a Aa aa
```
3. Offspring Genotypes: The Punnett square shows the following possible genotypes in the offspring:
* AA: Homozygous dominant (expresses the dominant trait)
* Aa: Heterozygous (expresses the dominant trait)
* aa: Homozygous recessive (expresses the recessive trait)
4. Offspring Phenotypes: Since the recessive trait only shows up when two recessive alleles are present, only offspring with the aa genotype will express the recessive phenotype.
Probability
The probability of producing an offspring with the recessive phenotype (aa) is 25%, as one out of four possible combinations in the Punnett square results in the aa genotype.
Example
Let's say the trait is eye color, and the dominant allele (A) codes for brown eyes, while the recessive allele (a) codes for blue eyes.
* Two parents with brown eyes (both Aa) can have a child with blue eyes (aa) because each parent contributes the recessive "a" allele.
