MODEL
Monohybrid crosses
Compare all single-locus parent combinations.
03 / GENETIC CROSSES
Predict the possibilities.
Choose two parent genotypes for a single gene. Each parent passes one allele to its offspring. A is completely dominant to a.
Try this: a test cross
Cross Aa with aa. Half of the expected offspring are Aa and half aa: a 1:1 phenotypic ratio. Crossing AA with aa instead produces only Aa offspring.
| Gametes | A | a |
|---|---|---|
| A | AA25% | Aa25% |
| a | Aa25% | aa25% |
These are probabilities for each offspring, not a guarantee that a family of four will contain one offspring from each square.
Assumes a diploid organism, one autosomal gene, equal gamete probabilities, random fertilisation and complete dominance. Linkage, sex linkage, mutation and viability differences are outside this model.
Explain what you observed
Must a dominant allele be the most common?
Your study notes
Take the next step
Connect this activity with your lesson notes and chapter practice.
Read a related learning guide →Practise Inheritance →Open the student notes folder ↗Concepts and sources
Curriculum connections: 10.1. Selected concepts.
Read the supporting source ↗PMDC curriculum ↗Questions and explanations are original teaching material; these are not official exam questions.