Certain traits, such as color blindness, are determined by an X-linked recessive gene. A couple in which both have normal vision have a color-blind son. The probability of this couple having a daughter who is a carrier is

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Many archeologists and anthropologists disagree with dr. thorne's view.  thorne strongly believes that what many calls "homo erectus"  was in fact  homo sapiens,  and that they migrated out of africa almost 2 million years ago and dispersed throughout europe and asia. that's way different  from what scientists have always believed about the evolution of the species.