To write a genotypic ratio, you determine the proportions of different genotypes that appear among the offspring resulting from a genetic cross. This involves identifying each specific genotype present and then counting the number of individuals (or counting the boxes in a Punnett square) that have each of those genotypes.
Based on the information provided in the reference, the process involves counting the individuals for specific genotype types:
The counting process, as illustrated in the reference, includes determining the number of occurrences for genotypes such as heterozygous and homozygous recessive:
- For heterozygous genotypes (which means having one dominant allele and one recessive allele, e.g., Aa), you count the number of individuals or boxes that show this genotype. The reference specifically states that for heterozygous, they counted "one two" which corresponds to a count of 2 in their example.
- For homozygous recessive genotypes (which means having two copies of the recessive allele, e.g., aa), you count the number of individuals or boxes that show this genotype. The reference states that for homozygous recessive, they counted "one" which corresponds to a count of 1 in their example.
Here are the counts for specific genotypes as noted in the reference:
| Genotype Type | Count (from Reference) |
|---|---|
| Heterozygous | "one two" (2) |
| Homozygous Recessive | "one" (1) |
After you have counted the number of individuals for each distinct genotype type present in the outcome of the cross (this typically includes homozygous dominant, heterozygous, and homozygous recessive in a monohybrid cross), these counts are then used to express the genotypic ratio, illustrating the relative frequency of each genotype among the offspring.
