What is the link between X-inactivation and potential hope for a new treatment for Down Syndrome? Question 7Answer a. Gene editing involving delivery of the XIST gene to inactivate one copy of chromosome 21 in cells. b. Gene editing to control a transcription factor affecting many other genes, similar to the SRY in males. c. Gene editing involving CRISPR Cas-9 in embryos to reduce copy number of important genes in cells. d. New pharmaceuticals that target spindle fiber reactivation like that for the X chromosome in females. e. Chromosome microdissection to remove key genes near the tip of chromosome 21 similar to the PAR.
Added by Gabriel A.
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Step 1: Understand the concept of X-inactivation, which is a process in female mammals where one of the two X chromosomes is randomly inactivated to ensure dosage compensation of X-linked genes. Show more…
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1. a. The vast majority of individuals with Down syndrome (Trisomy 21) result from fertilizations involving eggs with an extra chromosome 21 and normal sperm. (Where data are available, other trisomic conditions also result predominantly from eggs with extra chromosomes.) It is assumed that this is because of a nondisjunction event that occurred during meiosis in the mother. Based upon the duration of meiosis in females, suggest an explanation as to why females, particularly older women, produce aneuploidy gametes more often than do males.b. What are the two most commonly used methods of prenatal diagnosis for chromosome abnormalities? What are the advantages of each of the methods?
Adi S.
Question 1 What type of sequence-based element might be omitted by whole genome sequencing? What types of non-sequence based elements might be heritable? Question 2 How is it possible for two individuals with identical deletions to be affected by very different syndromes? What types of factors might play a role in determining the different phenotypic outcomes in the different individuals? Question 3 The process of X-inactivation occurs independently in each cell in the developing embryo. This means that females are effectively ________ for the X chromosome, meaning that different cells in their body effectively have different genotypes. Question 4 Dosage differences of the genes on the X chromosome between females and males are resolved by the process of ________.
Keemin L.
On the following figures, genes $A$ and $B$ are on the $X$ chromosome (blue) and both are subject to X inactivation, while genes $C$ and $D$ are on chromosome 17 (an autosome; $r e d$ ). $F$ and $S$ refer to alleles encoding fast- and slow-migrating forms of the corresponding proteins that can be discriminated by electrophoresis For women 2 and 3 in the figures that follow, indicate all the possible forms of the four proteins that could be expressed in clones made from different individual somatic cells that already had one or more Barr bodies. As an example, some clones from normal woman 1 could express the $A^{F}, B^{F}, C^{F}, C^{S}, D^{F}$ and $D^{S}$ proteins, while other clones could express the $A^{S}, B^{S}, C^{F}, C^{S}, D^{F},$ and $D^{S}$ proteins. None of the clones from woman 1 should make both the slow and fast forms of proteins A or B. Woman 2 is a heterozygote for a deletion of the XIC. Woman 3 is a heterozygote for a reciprocal translocation in which parts of the $X$ chromosome and chromosome 17 have exchanged places.
Sri K.
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