Chromosomal and Gonadal Sex: Inconsistencies

by Georgina Cornwall, PhD

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    00:01 Let’s ask a simple question. Obviously, we can have inconsistencies between chromosomal and gonadal sex.

    00:10 We’ll look at some of those examples. But is it possible that a human could be a full-on hermaphrodite? I’m going to leave that question with you as you think through this and what hermaphrodite really means.

    00:27 I’ll come back to answer that question at the end or perhaps you can. Hermaphrodite really means that the person or the individual can reproduce with itself. You probably have a little insight to the answer already.

    00:43 But let’s look at where some of these issues can come up with inconsistencies between chromosomal sex and gonadal sex, so XY females and XX males. It seems like that wouldn’t be possible and it turns out that it very much is possible. Here, we have a blown up version of the X and Y chromosomes.

    01:11 We have the pseudoautosomal region where a crossing over could happen. But if crossing over happens to happen outside of the pseudoautosomal region, that means that all that stuff that’s important on the Y chromosome for development of male sex and sex characteristics could end up on the X chromosome which will present some interesting situations. Here, we have a situation in which the SRY gene has been translocated through a crossing over event to the X chromosome, which means that the X chromosome now carries the SRY gene and can produce testis determining factor.

    01:58 We have an X that could end up making XX individual male. Then we could have a 46 XY individual that comes out female in the corresponding chromosome. We now have a Y chromosome that does not have an SRY and has some of the genes on it from an X. Those aren’t such a big deal but the not SRY part is the bigger deal there. Let’s take a look at some of the inconsistencies that come up, these DSD's, disorders of sexual development. That’s how you’ll see them presented fairly often.

    02:40 There are clearly multiple opportunities for things to go awry and have a DSD or disorder of sex development.

    02:50 We can see anything from complete gonadal dysgenesis, meaning you have an XX individual that actually has developed as an XY individual, right? So full-on male, full reproductive capacity, fertility and the works but the chromosomes say that they're a female. We’ll give you some insight into like when do we really call someone male or female. Is it about the X and the X or is it about the sexual development? Lots of different questions to consider in there. You could also have mixed gonadal dysgenesis which would mean one of each ovary and testis. Depending on the battle between hormones and many other factors that would perhaps end up creating one ovary and one testis, or the ovotestis situation, or we could go as far as having completely ambiguous genitalia.

    03:51 So, a baby comes out. It has, I don’t know what sex is the baby. That’s a good question. It used to be that we would reassign, not we because we weren’t around then, but doctors would reassign ambiguous genitalia always to be a female. That was because well, frankly, I guess it’s easier to make a functional-looking female that may not actually be functional. Now, we spend a little bit more time assessing where things may have gone wrong. So, there are lots of different steps along the way to consider of what sex we might end up wanting to make the individual. Sometimes it gets left a little later so that parents can have time to decide. So definitely, lots of different steps to consider along the way.

    About the Lecture

    The lecture Chromosomal and Gonadal Sex: Inconsistencies by Georgina Cornwall, PhD is from the course Chromosomal Disorders.

    Included Quiz Questions

    1. Translocation of SRY onto X chromosome
    2. Deletion of SRY on Y chromosome
    3. Translocation of SRY on long arm of Y chromosome
    4. Deletion of SRY on X chromosome
    5. Absence of Y chromosome
    1. Deletion of SRY on Y chromosome
    2. Translocation of SRY on X chromosome
    3. Translocation of SRY on long arm of Y chromosome
    4. Deletion of SRY on X chromosome
    5. Absence of Y chromosome

    Author of lecture Chromosomal and Gonadal Sex: Inconsistencies

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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