Changes

==History==

==History==

By 1900 scientists knew that cells were the building blocks of life, and that all living things start as a single fertilized cell which keeps dividing. Scientists identified tiny threads in the nucleus  of the cells which were called [[chromosome]]s because they could be stained with colored dyes for microscopic study - from the [[Greek]] words for colored bodies. They could see that chromosomes came in pairs, and that human cells all contained 23 matching pairs. American biologist [[Walter Sutton]] knew [[Mendel's principles of genetics|Mendel's]] work on peas, and suggested that chromosomes held the secret of inheritance.

By 1900 scientists knew that cells were the building blocks of life, and that all living things start as a single fertilized cell which keeps dividing. Scientists identified tiny threads in the nucleus  of the cells which were called [[chromosome]]s because they could be stained with colored dyes for microscopic study - from the [[Greek]] words for colored bodies. They could see that chromosomes came in pairs, and that human cells all contained 23 matching pairs. American biologist [[Walter Sutton]] knew [[Gregor Mendel|Mendel's]] work on peas, and suggested that chromosomes held the secret of inheritance.

Another American biologist, [[Thomas Hunt Morgan]], developed the idea that chromosomes were made up of linked groups of factors called genes. He experimented with red-eyed [[fruit fly|fruit flies]] and found that sometimes a white-eyed fly appeared. When he mated them, he found that as he expected there were three red-eyed flies to every white-eyed fly, but that all the white-eyed flies were male. He concluded that the gene for white eyes must be on a chromosome that was related to being male. Later workers found that this is why some hereditary diseases such as [[hemophilia]] and [[muscular dystrophy]] only show in males, though women can carry the gene for the disease without showing it.

Another American biologist, [[Thomas Hunt Morgan]], developed the idea that chromosomes were made up of linked groups of factors called genes. He experimented with red-eyed [[fruit fly|fruit flies]] and found that sometimes a white-eyed fly appeared. When he mated them, he found that as he expected there were three red-eyed flies to every white-eyed fly, but that all the white-eyed flies were male. He concluded that the gene for white eyes must be on a chromosome that was related to being male. Later workers found that this is why some hereditary diseases such as [[hemophilia]] and [[muscular dystrophy]] only show in males, though women can carry the gene for the disease without showing it.