Gender:  In the Genes or in the Jeans?

Section B

The appearances of typical males and females do not allow us to differentiate between these hypotheses. But scientists have been able to differentiate between these two hypotheses by observing certain unusual situations.

Sometimes errors occur during the meiotic divisions that lead to gamete formation (sperm and eggs). Instead of each sex chromosome going to a different gamete, two of these chromosomes might fail to separate, and so end up going to a single gamete, while the sister gamete would then get no sex chromosome. In other words, gametes may occur that either lack any sex chromosome or that have extra sex chromosomes.

If one of these gametes participates in fertilization, a zygote is produced with a genotype that differs from the usual XX and XY. By observing these uncommon genotypes, scientists are able to differentiate between these two alternative hypotheses.

Fill in the table below with the words "male" or "female" to indicate which phenotype you’d expect to see if hypothesis 1 were correct, and which you’d expect if hypothesis 2 were correct.

Questions

1. Which of these individual(s) would allow you to distinguish between these two hypotheses?
    
2. What phenotypes actually develop in the conditions described in this table?
    
3. Based on this evidence, which hypothesis now seems to better explain the role of sex chromosomes in determining an individual’s sex?
    
4. Based on what you know so far, what is the logical explanation for Terry’s inability to find a Barr body in her buccal smear?
    
5. Fill in the chromosome part of the flowchart to indicate what determines sexual differentiation at the level of the chromosomes.

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