Explain why linked genes do not assort independently. Linked genes tend to be inherited together because they are located on the same chromosome. Distinguish between parental and recombinant phenotypes.
• Map units indicate relative distance and order, not precise locations of gene. Distinguish between linked genes and sex-linked genes. Linked genes: genes located close enough together on a chromosome that they tend to be inherited together. Sex-linked genes: a gene located on either sex chromosome.
Explain how crossing over can unlink genes. In crossing over, which occurs while replicated homologous chromosomes are paired during prophase of meiosis 1, there is an exchange of one maternal and paternal chromatid, end portions of two nonsister chromatids trade places each time a crossover occurs.