OCR A Biology
Genes Bv Autosomal Linkage Crossing Recombinant Unexpected Ratio
Autosomal linkage, where genes are on the same non-sex chromosome, causes deviations from expected ratios as alleles are inherited together, with recombination frequency used to map gene locations.
Autosomal linkage, where genes are on the same non-sex chromosome, causes unexpected ratios because alleles tend to be inherited together. Recombination frequency, calculated from offspring ratios, indicates gene proximity on the chromosome.
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Unexpected ratio - Autosomal linkage |
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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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OCR A Biology