The Test Cross
1. The Setup:
- You need to cross your plant with yellow peas (unknown genotype) with a plant that is homozygous recessive for green peas (yy). This is called a test cross.
2. Why it Works:
- A homozygous recessive plant (yy) will always contribute a recessive allele (y) to its offspring.
- If the yellow pea plant is homozygous dominant (YY), all its offspring will inherit a dominant Y allele and be yellow.
- If the yellow pea plant is heterozygous (Yy), half its offspring will inherit a dominant Y allele and be yellow, and half will inherit a recessive y allele and be green.
3. The Experiment:
- Cross-pollinate your yellow pea plant with a plant that produces green peas.
- Observe the offspring (the F1 generation).
Interpreting the Results:
* All offspring are yellow: The yellow pea plant was homozygous dominant (YY).
* Some offspring are yellow, some are green: The yellow pea plant was heterozygous (Yy).
Example:
Let's say you have a plant with yellow peas and you want to know its genotype. You cross it with a plant that has green peas (yy).
* Scenario 1: All offspring are yellow. You can conclude that the yellow pea plant was homozygous dominant (YY).
* Scenario 2: Half the offspring are yellow, and half are green. You can conclude that the yellow pea plant was heterozygous (Yy).
