Autosomes: Structural Abnormalities

by Georgina Cornwall, PhD

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    In this lecture, we’ll move on to look at structural abnormalities of the autosomes. To begin, let’s look at how some of those abnormalities happen. We should be pretty familiar with the fact that there could be duplications of regions of the chromosome as well as deletions of regions of the chromosome. We have also seen that this could happen through translocations, exchange of pieces between chromosomes. Now, let’s introduce some new terminology. How do we express? We’ve talked about the Goldilocks principle with a large bowl, a small bowl, and just the right amount. Overexpression is when we have too much. That’s clear. Then, there’s another term, haploinsufficiency. It means having half of the genetic information that one should. Although this can happen in whole chromosomal deletions or additions, aneuploidies and polyploidies, we can also see overexpression or haploinsufficiency for genes encoded within the deleted or duplicated or translocated sections. Let’s look at first, a deletion situation. Cri-du-chat is a condition that you’ll be required to know. Cri-du-chat gets its name because people that are are suffering from it have a specific cat-like cry. Obviously, that’s how it got its name. It results from a deletion in the short arm p region of chromosome 5. So, we call that 5p. You can see the megabase numbers indicated there. You don’t need to know those specifically. The break of the chromosome though can be highly variable. That means that the expression of this disorder is highly variable. The break could involve an interstitial, so a region in the middle of that short arm or it could be a terminal deletion, a short terminal deletion or a longer terminal deletion. You can see exhibited in these sections in red over here that mental retardation is a large component of cri-du-chat. But...

    About the Lecture

    The lecture Autosomes: Structural Abnormalities by Georgina Cornwall, PhD is from the course Chromosomal Disorders.

    Included Quiz Questions

    1. A deletion of a region of the short arm of chromosome number 5
    2. A deletion of a region of the long arm of chromosome number 5
    3. Trisomy of chromosome 5
    4. A duplication of a region of the long arm of chromosome number 5
    5. A duplication of a region of the short arm of chromosome number 5
    1. Through de novo mutation
    2. By nondisjunction during meiosis before fertilization
    3. By nondisjunction during mitosis after fertilization
    4. Through Robertsonian translocation of short arm of chromosome 5
    5. By inheriting defective chromosome from a parent
    1. Hypertelorism - an abnormally increased distance between the eyes
    2. Epicanthus - characteristic cat-like cry
    3. Retrognathia - a fold of skin extending vertically over the inner angle of the eye
    4. Microcephaly - small receding chin
    5. Cri-du-chat - mental retardation

    Author of lecture Autosomes: Structural Abnormalities

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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