Monoallelic Expression

by Georgina Cornwall, PhD

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    Now, we also can have monoallelic expression. That is only one allele is expressed. We’re not talking about the X-inactivation where one is crumpled up. But for some reason and it could be random, we may only have expression of one allele. So, let’s look at some of the ways in which we might get monoallelic expression. First of all, we could have a random choice as I just said. It could happen because of genomic imprinting. We’ll take a look at both of those cases as well as it happening from X-inactivation. So these are three distinct ways that we may end up with only one allele being expressed even though both of them are actually there. So, when we look at monoallelic expression being a random choice, there are two possibilities that have surfaced. One of those is allelic silencing, where literally one allele is silenced by epigenetic mechanisms. So, either we have DNA methylation or histone modification or one of the epigenetic mechanisms that literally makes the DNA inaccessible to the transcriptional process. The other means we could have is by somatic rearrangement. This is one of those places where we talked about having an inversion. Let’s say the inversion happened right within a gene. So, the breakpoint from one of the ends of the inversion is right in the middle of the gene. That piece of DNA flips and is inserted back in. Now, we’ve broken a gene. So randomly, that gene may no longer be able to be expressed leaving only one allele or monoallelic condition. The next thing we have to consider is genomic imprinting. Genomic imprinting is going to come up in much more detail when we look at it in the lectures on single-gene disorders. Because genomic imprinting is something that happens...

    About the Lecture

    The lecture Monoallelic Expression by Georgina Cornwall, PhD is from the course Introduction to Medical Genetics. It contains the following chapters:

    • Monoallelic Expression
    • Monoallelic Expression: X-Inactivation

    Included Quiz Questions

    1. One allele is not present in the genome.
    2. One allele is randomly chosen.
    3. One allele is imprinted to not get expressed.
    4. One allele is part of the inactivated X chromosome.
    5. One allele is epigenetically silenced.
    1. Genomic Imprinting follows Mendelian inheritance.
    2. Some conditions may have different manifestations based on whether the mutation is paternally imprinted or maternally imprinted.
    3. Imprints are re-established during gametogenesis.
    4. Imprints remain part of our whole life (developmental and adulthood).
    5. Genomic Imprinting is an example of epigenetic inheritance.
    1. Barr body
    2. Barr chromosome
    3. Bar chromosome
    4. Bar body
    5. Bar allele
    1. Allelic dominance
    2. Epigenetic modifications
    3. X-inactivation
    4. Genomic Imprinting
    5. Barr body formation

    Author of lecture Monoallelic Expression

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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