story Set?2 In this section, you will find a series of questions that relates to
ID: 208051 • Letter: S
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story Set?2 In this section, you will find a series of questions that relates to the same overall information. There are clear problems to solve in this story set, so pay attention to where those arise an sure to review the coversheet information about problem-solving steps. Consider this... Genomic imprinting has been documented in a variety of mammals. In humans, one of the best examples of genomic imprinting has been documented through the inheritance of Angelman Syndrome and Praeder-Willi Syndrome. A. Explain what genomic imprinting is; then, using Praeder-Willi and Angelman Syndromes and describe exactly how these two different syndromes occur through the genomic as the basis for your answer, explain the mechanism for how genomic imprinting works imprinting mechanism that Sometimes, an error in meiosis results in an extra chromosome in a gametic cell, such as seen in Martha's egg cell. The event that results in a single extra chromosome is referred to as nondisjunction, which can happen in either Anaphase I or Anaphase II of Meiosis. B. First, explain how a failure in meiosis at Anaphase I or at Anaphase II could result in a single extra chromosome (such as an extra sex chromosome or an extra chromosome #21) in a gametic cell. In your answer,tackle cach in turn (Anaphase I and Anaphase I) as separate occurrence in different gametic cells. In other words, a gametic cell will either have had nondisjunction in Anaphase I or in Anaphase II but not bo meiosis. th in the same cell undergoing A unique feature of imprinted conditions is the unusual situation in which a both copies of a chromosome from one parent and none from the other. This is knouw uniparental disomy (UPD). Now that you've thought through some background information, consider this: child inherits disomy usually ars due to an error in meiosis. Two chromosomes in either get passed to the fetus. As a result, the fetus inherits egg or sperm three chromosomes (trisomy) rather than two. In relatively rare situation chromosomes is lost (termed trisomy rescue), resulting in a normal (disomic) after fertilization. uniparental disomy, i.e., a situation where the resulting off chromosomes where both chromosomes pair One-third of the time, this loss of the third chromosome will resul offinghas a pair of homologous t in in the pair came from either his father or his mother. somy (following trisomy rescuej could result in either one Willi Syndrome rescue) could result in either one C. Based on your knowledge of Angelman's Syndrome or the other of these genetic phenomena. Be syndromes involved. Explain your logic. specific in your hypothesis as th ere are twoExplanation / Answer
(A) Genomic imprinting: In normal two working copy of gene is inherit ,one from mother and one from father But in genomic imprinting only one working copy of gene is inherited either from single parent and other copy is epigenetically silenced during egg/sperm formation by methylation process. So, certain genes remains silenced in sperm or egg throughtout the life.
Example: Both Prader-Willi syndrome and the Angelman syndrome are caused by the loss of function of imprinted genes in proximal 15q. In approximately 2%-4% of patients, this loss of function is due to an imprinting defects.
In most cases of Prader-Willi syndrome chromosome 15 is actively transmitt from father as a result of imprinting but here loss of this imprinted gene from father may result into this syndrome.because the genes on the paternal copy have been deleted, and the genes on the maternal copy are turned off (inactive).
Angelman syndrome occurs due to the loss of function of a gene called UBE3A. In normal case most people inherit one copy of the this gene from each parent. Both copies of this gene are active in many of the body's tissues. But in certain areas of the brain, however, only one of copy is inherited from a person's mother ( maternal copy) is active. This parent-specific gene activation is caused by a phenomenon called genomic imprinting. If the maternal copy of the UBE3A gene is lost because of a chromosomal change or a gene mutation, a person will have no active copies of the gene in some parts of the brain.
B) Nondisjunction: It is failure of separation of a pair of homologous chromosome during anaphase 1 resulting into one extra cromosome in daughter cell. But if this happens during anaphase 2 then pair of sister chromatids doesn't get separaed resulting into n+1 and n-1 condition.
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