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← Sex Chromosomes

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Showing Revision 1 created 09/27/2013 by Cogi-Admin.

  1. Using this set of chromosomes, we would expect a
  2. female to develop. If we look just at the sex
  3. chromosome pair here, we see that we have two x's.
  4. And two x's means that we don't have a y.
  5. A y is what triggers male development, so in
  6. the absence of the y chromosome, it means that we're
  7. going to get female development. In humans, all females are
  8. genetically xx. They have two x chromosomes. And all males
  9. are genetically xy. They have 1 x and 1
  10. y chromosome. Now, there's no yy combination that exists in
  11. reality. And it's for two main reasons. The first
  12. is that you only have two parents, a male and
  13. a female. So you have someone XX and someone
  14. XY. So there's only one Y to pass down to
  15. the next generation anyways. So, getting a second Y
  16. just really isn't even possible, normally speaking. And the second
  17. reason is that the Y chromosome is a
  18. lot smaller than the X. There's actually a lot
  19. of important information that's on the X chromosome here
  20. that's not on the Y, and without that information,
  21. a human without an X chromosome can't survive.
  22. So you always need at least one X chromosome,
  23. and although there are actually variations on this theme
  24. here. The only two real combinations that we'll talk
  25. about are the XX combination, which develop as
  26. females, and the XY combination, which develop as males.