Answer:
Variation in skin pigmentation–skin and hair color—between people of differentgenetic ancestries is one of the most striking human characteristics (84). Study,and selection, of animals with particular pigmentary phenotypes has been of eco-nomic importance (5, 54,55); pigmentation in the mouse and birds are classicalexperimental systems to study gene action (5,54,55,104); and at the same time,even among nonexperts, it is widely understood that human skin color and haircolor are largely under genetic control, reflecting a person’s genetic heritage (97).One would have expected, therefore, the study of the genetics of skin and haircolor in man tobe a subject of much study: it isn’t. For instance, weremain almostcompletely ignorant of such simple issues as the mode of inheritance of blondehair. Indeed, although textbooks frequently refer to hair or eye color as an exampleto illustrate the role of genetics in understanding human diversity of form, until re-cently little was known of the genetic mechanisms underpinning normal variationin skin and hair color (14,97).Over the past ten years this situation has begun to change (5, 54,56,93,106).Advances based on the asset of the mouse fancy (5,55,104), coupled with the fa-cilityof modern molecular technology,have allowedtheidentificationof a numberof genes important in the determination of skin and hair color in man. The geneticsof many Mendelian disorders of medical importance such as albinism (63) havebecomeclearer:Existingclinicalclassifications have been showntobeinadequate,and mechanistic likenesses between what were once thought to be distinct pro-cesses outlined (63). This review briefly discusses these conditions, but takes as itsfocus advances in our understanding of pigmentary variation within what may bearbitrarily,butusefully, defined as the normal population,
Explanation:
Linked genes most likely account for such phenomena as red hair being strongly associated with light complexioned skin among humans. If you inherit one of these traits, you will most likely inherit the other.
Genetic linkage of this sort can be naturally ended. During the first division of meiosis, sections near the ends of chromosomes commonly intertwine and exchange parts of their chromatids with the other chromosome of their homologous pair. This process of sections breaking and reconnecting onto a different chromosome is called crossing-over. In the example shown below, "A" and "B" are unlinked by this process.
