karyotypes and nondisjunction april 2, 2009. some inherited traits can be identified at the...
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Karyotypes and NondisjunctionKaryotypes and Nondisjunction
April 2, 2009April 2, 2009
Some inherited traits can be identified at the chromosome level.
Geneticists use karyotypes.Chromosomes are stained.A photomicrograph is taken of a cell’s
chromosomes during metaphase.Chromosomes pairs are arranged in order of
decreasing size.
Test Benefit Risk
Amniocentesis• Diagnosis of chromosome abnormalities• Diagnosis of other defects
• Discomfort for expectant mother
• Slight risk of infection• Risk of miscarriage
Chorionic villus sampling
• Diagnosis of chromosome abnormality• Diagnosis of certain genetic defects
•Risk of miscarriage•Risk of infection•Risk of newborn limb defects
Fetal blood sampling
• Diagnosis of genetic or chromosome abnormality
• Checks for fetal blood problems and oxygen levels
• Medications can be given to the fetus before birth
• Risk of bleeding from sample site
• Risk of infection• Amniotic fluid might leak• Risk of fetal death
Amniocentesis procedure
Cell division in which either the homologous pairs or sister chromatids do not separate correctly, resulting in gametes with an abnormal number of chromosomes.
Monosomy – having only one of a particular type of chromosome.Trisomy – having a set of three chromosomes of one kind
e.g. Down syndrome (Trisomy 21)Results in distinctive facial features, short stature, heart defects, and mental disability
Females can survive with only one X chromosome or with three. Males can survive with either an extra X or an extra Y. Males cannot survive with only a Y chromosome.
Genotype
XO XXX XXY XYY OY
Phenotype
Female with Turner’s
syndrome (sterile)
Nearly normal female
Male with Klinefelter’s syndrome (sterile)
Normal or nearly normal
male
Results in death
Biggs, Haggins, Holliday. Biology (Glencoe Science)(Teacher Wraparound Edition). New York: GLENCOE MCGRAW HILL, 2007.
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Downschild. Digital image. About Downs Syndrome. 2008. The Coventry and Rugby Down's Syndrome Support Group. 01 Apr. 2009 <http://www.downssupport.org.uk/aboutdowns.html>.
"Genetics and pregnancy loss." Miscarriage Management™ -. 2009. Sydney IVF Limited. 01 Apr. 2009 <http://www.miscarriage.com.au/basepage.cfm?id=16>.
Karyotype. Digital image. AP Biology. 01 Apr. 2009 <http://www.nkellogg.com/apbiology.htm>.
Nondisjunction. Digital image. 01 Apr. 2009 <http://porpax.bio.miami.edu/~cmallery/150/mendel/heredity.htm>.