Six of the seven traits studied by Mendel (shape of the ripe seeds, color of the endosperm, color of the seed skin, color of the ripe pod, color of the unripe pod, different flower distributions, and length of the stem) are incidentally encoded by genes found in different chromosomes, which supports Mendel’s law of independent assortment. However, this is not always the case with all traits. When two genes are found close to one another on the same chromosome, the genes are usually inherited as a single unit. This phenomenon is called “genetic linkage.” Color blindness and hemophilia in humans were the first examples of this phenomenon in which the responsible genes were found to be consistently linked together, and subsequently, it became clear that their loci (positions of the genes on the chromosome) are present near the long arm of the X chromosome.

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