Incidence of Gen

Incidence of Gen - developing Alzheimer’s Down Syndrome...

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Incidence of Gen etic Abnormalities Maternal Age At 25 years, 17% of secondary oocytes may have chromosomal abnormalities. At 40 years, up to 74% may contain abnormalities. Spontaneous Abortion (Miscarriage) Two-thirds of all pregnancies are lost. These miscarriages are called spontaneous abortions . Genetic mutation causes an estimated 60% of these spontaneous abortions. Autosomal Abnormalities Nine percent of spontaneous abortions are trisomy 13, 18, or 21; but 0.1% of newborns have these trisomies. Down Syndrome Down syndrome is trisomy 21. It is characterized by mental retardation, an abnormal pattern of palm creases, a flat face, sparse, straight hair, and short stature. People with Down syndrome have a high risk of having cardiac anomalies, leukemia, cataracts, and digestive blockages. Life expectancy of Down syndrome individuals is in the middle teens but some live much longer. The gene responsible for Alzheimer’s is on chromosome 21. Down’s are at increased risk for
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Unformatted text preview: developing Alzheimer’s. Down Syndrome is associated with maternal age. Older women, particularly those older than 40, are more likely to have a Down Syndrome child. Translocation Down Syndrome A translocation is the movement of a chromosomal segment from one chromosome to another nonhomologous chromosome. Five percent of Down Syndrome cases involve a translocation. The translocation often involves chromosome 14. In the translocation diagrammed below, chromosome #21 has become fused with chromosome #14. During meiosis, the two chromosomes might align so that each daughter cell receives one chromosome 21 as shown below. This will produce a normal egg. If the chromosomes align as illustrated below, one daughter cell will receive two chromosome 21s and the other will not receive any. When a gamete with two 21s fuses with a normal gamete, the result is a zygote with three chromosome 21s. This form runs in families and is not age-related....
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Incidence of Gen - developing Alzheimer’s Down Syndrome...

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