KARYOTYPING Honors Biology

What and How? Used as a way to “see” the chromosomes Pairs up homologous chromosomes Allows for detection of several genetic disorders slow and deliberate process Cells are taken from the amniotic fluid surrounding embryo (amniocentesis) also taken from blood Nucleus is frozen during meiosis Photograph of chromosomes is taken

How to... (II) Chromosomes are lined up from longest to shortest, then paired Homologous chromosomes are matched up by their “like” characteristics –size (length) –centromere location –band pattern a pattern of dark and light bands that shows up approximately the same on each chromosome

Normal Male Karyotype

Normal Female Karyotype

Nondisjunction Failure of homologous chromosomes to separate normally during anaphase I –centromere does not split, so both chromosomes go to same side of the cell Results in an extra copy of the chromosome in some gametes, and a loss of such in others Can occur in sex chromosomes or autosomes –not all nondisjunctions develop fully

Down’s Syndrome Caused by Trisomy 21 3 copies of 21st chromosome More common in women over 35 Symptoms include –mental retardation –large protruding brows –generally short stature

Down’s Syndrome Karyotype

Klinefelter’s Syndrome Also known as Trisomy 23 (47XXY) Caused by abnormal xy gamete from male Male patients –sterile –“less male” in appearance

Klinefelter’s Karyotype

Turner’s Syndrome Caused by monosomy 23 (45XO) Fertilization of gamete without a 23rd chromosome Sterile females –sex organs do not develop –look normal

Turner’s Karyotype