Karyotypes and Nondisjunction KARYOTYPE Definition n Picture of
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Karyotypes and Nondisjunction
KARYOTYPE: Definition n Picture of chromosomes taken during metaphase (mitosis) when chromosomes are fully condensed n Chromosomes are arranged large to small by homologous pairs – sex chromosomes shown last n Normal human karyotypes show 46 chromosomes – 44 autosomes (22 pairs of homologous chromosomes) – 2 sex chromosomes
KARYOTYPE: Human Chromosomes
KARYOTYPE: How it is useful n In order to study differences in size, shape, and chromosome number (too few or too many) n Determines the sex of the child n Usually done for humans when a known chromosomal disorder runs in family – (i. e. Down Syndrome) n Can be done for any organism
NONDISJUNCTION: Definition and Results n Form of chromosomal mutation during meiosis when homologous chromosomes fail to separate n Results in abnormal number of chromosomes in gametes, which can possibly lead to a disorder in the offspring
NONDISJUNCTION: Examples of Disorders n Down Syndrome – (autosome) - three copies of chromosome 21 – Karyotype shows 47 chromosomes (Trisomy 21) – Results in various degrees of mental disabilities, causes decrease immunities to diseases/organ defects, distinguished facial features n Edward’s Syndrome – (autosome) three copies of chromosome 18 – Karyotype shows 47 chromosomes (Trisomy 18) – Results in failure of all organ systems, death after a few months
NONDISJUNCTION: Examples of Disorders n Turner’s Syndrome – (sex chromosome) – only one X chromosome is inherited – Karyotype 45, X – Results in sterile female, short in stature, heart and kidney defects n “Superfemale” – (sex chromosome) – extra X chromosome is inherited – Karyotype 47, XXX (Trisomy X) – Results in healthy, fertile female
NONDISJUNCTION: Examples of Disorders n Klinefelter’s Syndrome – (sex chromosome) –extra X chromosome(s) is/are inherited – Karyotype 47, XXY (or even 48, XXXY; 49, XXXXY) – Usually results in sterile male n “Supermale” – (sex chromosome) – extra Y chromosome is inherited – Karyotype 47, XYY – Usually results in sterile, more violent, decreased intelligence, taller male