BiologyPrinciples of inheritance and variationClass 12

Mendelian dihybrid cross & Morgan’s linkage: interactive simulation

Mendel’s dihybrid cross of round yellow seeds (RrYy × RrYy) demonstrates that traits segregate independently, producing 4 distinct phenotypes in a 9:3:3:1 ratio.

Useful for: NEET, CBSE Boards

Try this

T.H. Morgan discovered that genes located on the same chromosome do not assort independently if they are physically linked. Tightly linked genes (Cross A: yellow body and white eye) show only 1.3% recombination, while loosely linked genes (Cross B: white eye and miniature wing) show 37.2% recombination.

  1. 1

    In the Punnett Square, click on "Wrinkled Green".

    What you should see

    Only 1 out of 16 boxes (6.25%, rryy) has this double-recessive phenotype.

  2. 2

    Switch to "Morgan’s Gene Linkage" and click "Cross A (y & w)".

    What you should see

    The genes are just 1.3 cM apart. Parental phenotypes remain 98.7% and recombination is only 1.3% because cross-overs rarely occur in tight spaces.

  3. 3

    Drag the gene distance slider to 50 cM.

    What you should see

    Recombination reaches its theoretical maximum of 50%, behaving exactly like Mendel’s independent assortment.

Formulas behind it

Dihybrid Phenotypic Ratio

9:3:3:1(Round Yellow : Round Green : Wrinkled Yellow : Wrinkled Green)9 : 3 : 3 : 1 \quad (\text{Round Yellow : Round Green : Wrinkled Yellow : Wrinkled Green})

Recombination Frequency

Recombination %=Number of RecombinantsTotal Progeny×100=Distance in cM\text{Recombination }\% = \frac{\text{Number of Recombinants}}{\text{Total Progeny}} \times 100 = \text{Distance in cM}

Maximum Recombination Limit

Max Recombination=50%(Indistinguishable from unlinked)\text{Max Recombination} = 50\% \quad (\text{Indistinguishable from unlinked})

Common mistakes

  • Assuming recombination frequency can exceed 50%. Even with infinite distance, recombination never exceeds 50% between two linked loci.
  • Thinking linked genes violate the Law of Segregation. Linkage violates Independent Assortment, NOT Segregation.
Stuck on a mendelian dihybrid cross & morgan’s linkage question?Snap it and get a whiteboard video solution.

FAQ

Who constructed the first genetic map?

Alfred Sturtevant (Morgan’s student) utilized the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes (1 map unit = 1 centiMorgan = 1% recombination).

Why did Morgan choose Drosophila melanogaster for genetics?

Drosophila breeds quickly on simple synthetic medium, produces hundreds of offspring in a single mating, has a short life cycle of about 2 weeks, and displays clear sex-dimorphism.

Related simulations

All 65 simulations
DNA double helixBiology, Class 12Nephron & counter-current mechanismBiology, Class 11 & Class 12Sliding filament theory & muscle contractionBiology, Class 11 & Class 12Action potential & synaptic transmissionBiology, Class 11 & Class 12Cell explorerBiology, Class 8 & Class 9 & Class 11Human heart and blood flowBiology, Class 10 & Class 11

Want a specific topic or simulation added?

Tell us in our feedback box which chapter or concept you want visualised next.

Send feedback