When working out a dihybrid cross
Autosomes: these are chromosome pairs that do not determine sex and are identical in appearance (Same size and gene loci)
Sex Chromosomes: these are chromosome pairs that are not identical in appearance ( X and Y chromosome in humans) and are used to determine sex
During prophase I, non-sister chromatids of a homologous pair can break, exchange parts of the genetic material, then reform at certain points called chiasmata. The non-sister chromatids that originate from the maternal and paternal alleles will now have new gene combinations.
Linkage groups: genes are linked when they are located on the same chromosome (loci are on the same chromosome). They are usually inherited together as they cannot be separated other than through recombination. Linked genes, therefore do not follow Mendel's Law of Independent Assortment
Linked genes do not followed the expected phenotypic ratio of a dihybrid cross of 9:3:3:1. The expected phenotypic ratio would follow the monohybrid cross and produce phenotypes similar to the parents. Any recombinant phenotypes are usually quite easy to spot as they will appear in low percentages or none at all. This is because crossing over rarely occurs in prophase I. The recombinants of linked genes are not found in parents.
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