Lecture 32: Numerical Chromosomal Abnormalities and Nondisjunction Meiosis l Meiosis‖l Centromere-linked markers
Numerical Chromosomal Abnormalities and Nondisjunction Lecture 32: • Meiosis I • Meiosis II • Centromere-linked markers
Female XX Male 46.XY Human chromosomal abnormalities may be numerical or structural Numerical Total chromosomes/ cell Trisomy 3 copies of a single chromosome Monosomy 1 copy of a single chromosome 45 Triploidy 3N 69 Tetraploidy= 4N 92 Structural Deletion Duplication Translocation (involves 2 chromosomes
Female Male 46,XX 46,XY Human chromosomal abnormalities may be numerical or structural. Numerical Trisomy = 3 copies of a single chromosome 47 Monosomy = 1 copy of a single chromosome 45 Triploidy = 3N 69 Tetraploidy = 4N 92 Structural Deletion Duplication Translocation (involves 2 chromosomes) Total # chromosomes / cell
Chromosomal abnormalities manifest themselves in two ways 1)Spontaneous abortions 50% of human pregnancies--> spontaneous abortion or miscarriage nearly all during first trimester of pregnancy, with many during the first month, when pregnancy is recognized only y hormonal assays 50% of spontaneously aborted embryos and fetuses have chromosomal abnormalities Therefore 25% of all human embryos have chromosomal abnormalities
Chromosomal abnormalities manifest themselves in two ways: 1) Spontaneous abortions of human pregnancies --> spontaneous abortion or miscarriage of spontaneously aborted embryos and fetuses have chromosomal abnormalities nearly all during first trimester of pregnancy, with many during the first month, when pregnancy is recognized only by hormonal assays 25% of all human embryos have chromosomal abnormalities. 50% 50% Therefore
Breakdown of chromosomal abnormalities in spontaneous abortions Trisomy 16 15% 13, 18,21 9% XXX. XXY XYY 1% All others 27% Monosomy X (45, X or XO) 18% Triploidy 7% Tetraploidy 6% Other Total 100%
Trisomy XXX, XXY, XYY All others Monosomy X (45,X or XO) Triploidy Tetraploidy Other Total 15% 9% 1% 27% 18% 17% 6% 7% Breakdown of chromosomal abnormalities in spontaneous abortions: 100% 16 13, 18, 21
Chromosomal abnormalities manifest themselves in two ways 2 )Defects in newborns: 0.5% aggregate frequency among the most common XXY 1/1.000 males XYY /1.100maes 0双 1/7,500 females /1.200 females Trisomy 13 1/1500 Trisomy 18 1/1100 Trisomy 21 1/900 Structural anomalies 1/400
2) Defects in newborns: 0.5% aggregate frequency Among the most common: XXY XYY XO XXX Trisomy 13 Trisomy 18 Trisomy 21 Structural anomalies 1 / 1,000 males 1 / 1,100 males 1 / 7,500 females 1 / 1,200 females 1 / 15,000 1 / 11,000 1 / 900 1 / 400 Chromosomal abnormalities manifest themselves in two ways: