Meiosis with Crossing Over

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How are genes on the same chromosome inherited? An important fundamental of genetics is the idea of independent assortment. This states that genes are inherited independently of one another. Imagine an individual has two different alleles (versions of a gene) for eye color (blue and brown) and two different alleles for hair color (blonde and black). If a gamete produced by that individual contains the blue eye color allele it is has an equally good chance of containing the blonde or the black hair color allele. This can be true even if both genes are on the same chromosome. Chromosomes segregate during Meiosis I and you might expect that all genes on a chromosome would be inherited as a unit. However, during prophase I homologous chromosomes pair up and become attached to one another. At this time, crossing over moves sections of DNA between homologous chromosomes and allows for independent assortment.