In about 95 percent of cases of Down syndrome, this chromosomal abnormality results from _____ during formation of one parent's gamete
Added by Samuel M.
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- Down syndrome is caused by the presence of an extra copy of chromosome 21, known as trisomy 21. Show more…
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A couple has a child with down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?
Sri K.
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.
Although it seems rarely discussed in today's society, at least one third of all incipient human pregnancies end in miscarriage. The large proportion of those miscarriages result from 'chromosomal abnormalities,' which means nothing more and nothing less than errors in meiosis. Usually, this results from an incorrect number of homologous chromosomes ending up in the haploid egg or sperm cells—either too many or too few. In the case of chromosomes without many genes, like chromosome 21 which is represented by three copies instead of two in people with Down syndrome, or the sex chromosomes, the fetus may survive, but in the case of most of our 23 pairs of homologous chromosomes, the fetus will not successfully develop if there are not exactly 46 chromosomes in the zygote. Using the steps of meiosis, explain how this process of ending up with an incorrect number of chromosomes in the haploid sex cells could occur.
Madhur L.
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