LIFESCI 7B Chapter Notes - Chapter 3: Miscarriage, Patau Syndrome, Nondisjunction
4 Sep 2018
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Document Summary
Nondisjunction: failure of a pair of chromosomes to separate during anaphase. One receives an extra copy, one has no copy of that chromosomes. In meiosis, gametes have extra or missing chromosome. First division nondisjunction (more common; homologous chromosomes don"t separate) vs second division nondisjunction (sister chromatids don"t separate) Down syndrome: presence of extra copy of chromosome 21 (trisomy 21) Shorthand: 47+21 (individual has 47 chromosomes with an extra copy of chromosome 21) Having a baby with down syndrome increases as mother gets older. Trisomy 13 and trisomy 18 are also common, but newborns usually don"t survive the rst year of life. Extra/missing sex chromosomes have fewer effects that extra autosomes. Usually the extra sex chromosome is undiscovered until their chromosomes are examined. Xyy doesn"t show any phenotypic effects bc the y contains only a few functional genes other that the gene that makes the embryo develop into a male.
