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.

Farabee, M. J. Human Genetics. 2001. 01 Apr. 2009 <http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookhumgen.html>.

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>.