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Biology
Genetic linkage and recombination — Why are traits often inherited together?
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Follow chromosome segments through one meiosis, then sample gametes to compare genetic linkage with independent assortment.
Source H1Source H2
One example of meiosis — not a population frequency.
The slash separates homologous chromosomes. A locus is a gene’s position; A/a and B/b are alleles at two loci.
Locus positions are schematic, not a scale of genetic distance.
Paired duplicated chromosomes
Four chromatids, two loci. Follow the B/b segment when you press Play.
This model tracks alleles, not phenotypes. Uppercase does not mean better.
Four chromatids, two loci. Follow the B/b segment when you press Play.
Preparing resourceModel notes
- The model uses two hypothetical autosomal loci, A/a and B/b, in a double heterozygote. Dominance, phenotypes, mutation and gamete selection are not modelled.
- One meiosis is a conditional example with at most one crossover between nonsister chromatids. Four meiotic products do not imply four functional eggs.
- r is the theoretical recombinant gamete frequency (0–50%), not the fraction of cells with crossovers. Locus positions are not measured in bp or cM; multiple crossovers and interference are outside the model.
- Each draw represents one gamete from an independent meiosis. Finite counts vary; the observed recombinant fraction may exceed 50% while the theoretical r does not.
- Four equal probabilities of 25% may result from independent assortment or 50% recombination between loci on the same chromosome; that ratio alone cannot identify chromosome location.
- Co-inheritance of allele combinations helps explain linkage, but does not justify attributing every correlation between traits, particularly human traits, to this mechanism.