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Notes: Karyotypes s Human Chromosomes- what you know… • Humans have 46 chromosomes (diploid-2N) • 2 of them are sex chromosomes (X and Y) they determine what sex you are – XX = female – XY = male • 44 of them are autosomes they do not determine the sex of an individual. Sex chromosomes How is a KARYOTYPE Made? 1. Collect sample: a. Fetus: amniotic fluid collected during an amniocentesis or a piece of the placenta collected during a chorionic villi sampling test (CVS). b. Newborn: white blood cells 2. Separate dividing & non-dividing cells using chemicals 3. Culture the dividing cells to get a lot of cells 4. Add chemical to stop cell division when chromosome is compacted 5. Lyse the cells 6. Stain the chromosomes (stain sticks to regions with a lot of “A” and “T” bases 7. Analyze! How is a KARYOTYPE Analyzed? • Use computers to match the homologous pairs. • We will cut out the chromosomes from a chromosome spread then arrange them to match the banding patterns of the homologous pairs – Use banding patterns, size of chromosome, and position of centromere • This type of picture is called a KARYOTYPE Chromosome Spread Karyotype What does a Karyotype tell you? – Sex (male or female) – Irregular numbers of chromosomes – Any mutations in the chromosomes • Basically: all the chromosomes in a cell are displayed and can be examined for abnormalities Is this offspring a girl or boy? How do you know? Are there any abnormalities in this offspring? Chromosomal Disorders • Most of the time, the mechanisms that separate human chromosomes in meiosis work very well, but things can go wrong • The most common error: NONDISJUNCTION – The chromosomes fail to separate in Anaphase I or II – The result? Abnormal numbers of chromosomes in gametes. Nondisjunction Prefixes: dis = absence of / opposite of non = not Root Word: Junction = joining together • disjunction = the act of separating • nondisjunction = the act of not separating Figure 14-15 page 352 Metaphase I “Trisomy” = 3 copies of a chromosome Nondisjunction (after anaphase I) End of Meiosis—4 gametes produced Examples of Chromosomal Disorders • • • • Down Syndrome (3 #21 chromosomes) Klinefelter’s Syndrome (XXY) Turner’s Syndrome (XO) Triple X Syndrome (XXX) Examples of Nondisjunction resulting in Chromosomal Disorders • Down's Syndrome: 47 chromosomes with 3 #21 chromosomes. • Triple-X Syndrome: 47 chromosomes caused by 3 X chromosomes. • Klinefelter's Syndrome: 47 chromosomes caused by 2 X chromosomes and 1 Y chromosomes. • Turner's Syndrome: 45 chromosomes with 1 X chromosome (caused by the absence of one of the X chromosomes or a Y chromosome). Chromosomal Mutations • Chromosomal Mutations – Deletion – Duplication – Inversion – Translocation Chromosomal Mutation (change in number) • If an organism is born with the incorrect number of chromosomes – Ex: 47 human chromosomes instead of 46 • Result of nondisjunction Down Syndrome • 3 copies of chromosome #21 • 1 in 800 babies in the US is born with this disease • produces mild to severe mental retardation • May not live as long Klinefelter’s Syndrome • This is a sex chromosomal disorder associated with males. • Nondisjunction causes an extra X chromosome to be passed along during meiosis (XXY). • Resulting male cannot reproduce • Cases have been found in which individuals were (XXXY) or (XXXXY) • Decrease muscle mass and body hair Turner’s Syndrome • This is a sex chromosomal disorder associated with females. • Nondisjunction causes offspring to inherit only one X chromosome (genotype = XO). • Resulting female is sterile due to underdeveloped sex organs. • 1/2500 females Review question.. Who determines the sex of a child? The mother or the father? THE FATHER!!!! Why? Why does the father determine the sex of the offspring??? • Mom is XX: she can donate either one X chromosome or the other X chromosome to the offspring (mom can only donate an X) • Dad is XY: he can donate either an X chromosome or a Y chromosomes. – If the offspring receives an X from dad, it is female – If the offspring receives a Y from dad, it is male