Sex Determination

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Sex Determination
For the following slides make a list of
phenotypic traits that are different between
males and females.
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http//www.physorg.com/news177315628.html
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http//www.wwd.com/lifestyle-news/eye/joe-dimaggio
-and-marilyn-monroe-continued-1963733//?fulltrue
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Karyotypes
Female
Male
Brainstorm How is sex determined based on the
differences between the two karyotypes?
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Pick a hypothesis!

1. The presence of 2 X chromosomes cause the
   development of females
2. The presence of a Y chromosome causes the
   development of males
3. The presence of an X AND a Y chromosome causes
   the development of males
4. The presence of only one X chromosome causes the
   development of males.

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Other Karyotypes
Female
Male
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• Q Which is the best answer A, B, C or D?
• A B or C are the most probable with the
  information given.
• Q What karyotype is needed to distinguish
  between these two possibilities?
• A A karyotype with just Y, no X
• Q Why do you think this karyotype doesnt exist?
• A The X chromosome contains many essential genes
  unrelated to sex determination. An embryo with
  just Y would not be viable.

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XY Females Help Solve the Mystery!

• Male by karyotype, but phenotypically female
• How can this be???
• some found to have a deletion on the Y
  chromosome, a region scientists called the
  sex- determining region
• in 1990, Berta et al. found that some XY
  females have intact Y chromosomes, but have
  mutations in a single gene called SRY that is
  within the sex- determining region
• further work confirmed that in most mammals,
  the default sex is female and the SRY gene
  must express functional protein during
  development to produce males

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• Other systems of sex determination exist in other
  organisms

Are there sex chromosomes? Whats the pattern?
What determines the gender?
Figure 9.22 B
Figure 9.22 C
86F ? all female
86-93F ? mixed
93F ? all male
Figure 9.22 D
Cambell, Reece, Taylor, Simon, and Dickey.
Biology Concepts and Connections, 6th edition.
Benjamin Cummings Publishing. 2008.