2Chromosomal abnormalities Incorrect number of chromosomesnondisjunctionchromosomes don’t separate properly during meiosisbreakage of chromosomesdeletionduplicationinversiontranslocation
3NondisjunctionProblems with meiotic spindle cause errors in daughter cellstetrad chromosomes do not separate properly during Meiosis 1sister chromatids fail to separate during Meiosis 2too many or too few chromosomes2nn-1n+1n
5Nondisjunction Baby has wrong chromosome number trisomy monosomy cells have 3 copies of a chromosomemonosomycells have only 1 copy of a chromosomemonosomy2n-1trisomy2n+1
6Human chromosome disorders High frequency in humansmost embryos are spontaneously abortedalterations are too disastrousdevelopmental problems result from biochemical imbalanceCertain conditions are toleratedupset the balance less = survivecharacteristic set of symptoms = syndrome
7Down syndromeTrisomy 213 copies of chromosome 211 in 700 children born in U.S.Chromosome 21 is the smallest human chromosomebut still severe effectsFrequency of Down syndrome correlates with the age of the mother
9Down syndrome & age of mother Mother’s ageIncidence of Down SyndromeUnder 30<1 in 1000301 in 900351 in 400361 in 300371 in 230381 in 180391 in 135401 in 105421 in 60441 in 35461 in 20481 in 16491 in 12
10Genetic testing Amniocentesis in 2nd trimester Analysis of karyotype sample of embryo cellsstain & photograph chromosomesAnalysis of karyotype
11Sex chromosomesHuman development more tolerant of wrong numbers in sex chromosomeBut produces a variety of distinct conditions in humansXXY = Klinefelter’s syndrome maleXXX = Trisomy X femaleXYY = Jacob’s syndrome maleXO = Turner syndrome female
12Klinefelter’s syndrome XXY maleone in every 2000 live birthshave male sex organs, but are sterileSome have feminine characteristicstallnormal intelligence
13Klinefelter’s syndrome How many Barr bodies would you expect?
14Klinefelter’s syndrome How many Barr bodies would you expect?
15Jacob’s syndrome male XYY Males 1 in 1000 live male births extra Y chromosomesomewhat taller than averagemore activeslight learning disabilitiesdelayed emotional immaturitynormal intelligence, normal sexual development