2 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 areXX = femaleXY = male44 of them are autosomes they do not determine the sex of an individual.Sex chromosomes
3 How is a KARYOTYPE Made? Collect sample: Fetus: amniotic fluid collected during an amniocentesis or a piece of the placenta collected during a chorionic villi sampling test (CVS).Newborn: white blood cellsSeparate dividing & non-dividing cells using chemicalsCulture the dividing cells to get a lot of cellsAdd chemical to stop cell division when chromosome is compactedLyse the cellsStain the chromosomes (stain sticks to regions with a lot of “A” and “T” basesAnalyze!
4 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 pairsUse banding patterns, size of chromosome, and position of centromereThis type of picture is called aKARYOTYPE
7 What does a Karyotype tell you? Sex (male or female)Irregular numbers of chromosomesAny mutations in the chromosomesBasically: all the chromosomes in a cell are displayed and can be examined for abnormalities
8 Is this offspring a girl or boy? How do you know?
10 Chromosomal Disorders Most of the time, the mechanisms that separate human chromosomes in meiosis work very well, but things can go wrongThe most common error: NONDISJUNCTIONThe chromosomes fail to separate in Anaphase I or IIThe result? Abnormal numbers of chromosomes in gametes.
11 Nondisjunction Prefixes: dis = absence of / opposite of non = not Root Word:Junction = joining togetherdisjunction = the act of separatingnondisjunction = the act of not separating
12 End of Meiosis—4 gametes produced Metaphase IFigure 14-15page 352“Trisomy” = 3 copies ofa chromosomeNondisjunction(after anaphase I)End of Meiosis—4 gametes produced
16 Examples of Chromosomal Disorders Down Syndrome (3 #21 chromosomes)Klinefelter’s Syndrome (XXY)Turner’s Syndrome (XO)Triple X Syndrome (XXX)
17 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).
19 Chromosomal Mutation (change in number) If an organism is born with the incorrect number of chromosomesEx: 47 human chromosomes instead of 46Result of nondisjunction
20 Down Syndrome 3 copies of chromosome #21 1 in 800 babies in the US is born with this diseaseproduces mild to severe mental retardationMay not live as long
21 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 reproduceCases have been found in which individuals were (XXXY) or (XXXXY)Decrease muscle mass and body hair
22 Turner’s SyndromeThis 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
23 Review question.. Who determines the sex of a child? The mother or the father?THE FATHER!!!!Why?
24 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 femaleIf the offspring receives a Y from dad, it is male