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- unexpected ratio may be down to autosomal linkage
- autosomal linkage (linked genes found on non-sex chromosomes)
- sex linkage (linked genes found on sex chromosomes)
- e.g BbVv and bbvv crossed, gametes of homo is only bv, and gametes of hetero are mainly BV and bv (as these alleles linked), and few Bv and bV due to crossing over (so some of the linked genes seperated), and these form small no of recombinant offspring (diff combinations of alleles than either parent), closer the genes are on chromosome, less likley to be seperated (so fewer recombinant offspring)
- recombination frequency = no. of recombinant offspring/total no of offspring, its measure of amount of crossing over during meiosis, 50% means no linkage, less than 50% means gene linkage (so independent assortment hindered), so the less crossing over, the lower the % (so determines how close genes are on chromosome), so can map genes on chromosome
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