KHAEMENES ACADEMY · BIOLOGY 10 · WEEK 20 · DAY 04

Beyond Complete Dominance

Recognize incomplete dominance, codominance and multiple alleles as extensions—not violations—of segregation.

Safety, privacy and evidence boundary

Use fictional organisms, coins/cards, and published-style datasets. Do not require personal family histories, ancestry testing, fertility information, medical pedigrees, or personal genetic data. Trait inheritance never ranks human worth.

Explicit science instruction

Segregation can remain valid even when phenotype expression is not complete dominance. In incomplete dominance, a heterozygote has a distinct intermediate phenotype under the measured scale. In codominance, products of both alleles can be detected. A locus may also have more than two alleles in a population even though a diploid individual ordinarily carries only two copies.

These patterns change phenotype predictions while preserving allele segregation.

Worked example with reasoning

Fictional flower alleles R and W show incomplete dominance: RR red, RW pink, WW white. RW × RW predicts genotype and phenotype proportions 1/4 red, 1/2 pink, 1/4 white because each genotype has a distinct phenotype.

Guided question

How can a cross depart from a 3:1 phenotype ratio while still following segregation?

Independent work

  1. Model RW × RW.
  2. Compare genotype and phenotype ratios with complete dominance.
  3. Create a codominance example using fictional cell-surface markers.
  4. Explain why a population can contain three alleles while one individual carries two.

Investigation / Data Lab

Inheritance probability simulation

Question: How closely does a finite sample match the expected genotype ratio for RW × RW?

  1. Represent each parent with two cards or coin states, R and W. Randomly draw one allele from each parent for 40 simulated offspring, replacing and remixing after every draw.
  2. Record RR, RW, and WW counts without changing outcomes that seem unusual.
  3. Calculate observed proportions and compare them with the expected 1:2:1 model.
  4. Repeat or combine with a second 40-trial run and compare how sample size changes the deviation.
  5. Write one limitation: the simulation models segregation/fertilization probabilities, not viability, linkage, mutation, or environmental effects.

Evidence standard: preserve the raw tally, expected counts, observed counts, percent/proportion comparison, and one method revision.

Misconception check

Incomplete dominance does not mean alleles “blend permanently.” Alleles remain discrete and can segregate into later generations.

Formative understanding check

What phenotype ratio is expected in RW × RW under incomplete dominance?

Worked response

1:2:1 because all three genotypes are phenotypically distinguishable.

Open-book formative practice only; not an official mastery attempt or grade.

Mentor evidence conference

Ask Archaemenes to challenge your probability, evidence classification, model assumptions, and limitations. The mentor does not infer personal genetics or provide protected assessment answers.

Open Archaemenes

Teacher guidance

Foundation: use color-coded genotype cards. Core: separate segregation from phenotype mapping. Extended: compare molecular dosage explanations and cases where phenotype categories oversimplify quantitative traits.

Preserve learning evidence

Keep models, calculations, corrections, and limitations in the matching Week 20 evidence field.

Return to evidence workspace