BIOL 190 Lecture Notes - Lecture 17: Patau Syndrome, Sister Chromatids, Edwards Syndrome
Document Summary
Independent assortment- side by side orientation of each homologous pair of chromosomes is a matter of change. Every chromosome pair orients independently of the others during metaphase. Results in different combinations of chromosomes in gametes. Change in the structure and/ or number of chromosomes in a cell. Random errors during meiosis, usually not passed from one generation to the next. The result of nondisjunction or mistakes during crossing over. Aneuploidy - too few or too many chromosomes. Non- disjunction- error in chromosome/ chromatid separation in meiosis i or ii. Results in an incorrect number of chromosomes. Gamete ( n + 1) with 24 chromosomes (from non- disjunction event) Most autosomal trisomies are lethal; embryo/ fetus dies in utero (miscarriage) Babies usually die after a few months. Gamete (n-1) with 22 chromosomes (from non-disjunction event) Monosomies are lethal embryo/ fetus dies in uerto (miscarriage) Single exception- turner syndrome, individuals are (2n- 1) Translocation- attachment of a segment to a nonhomologous chromosome.