12-4 Changes in Chromosome Number
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Karyotype - A picture of a person's chromosomes, arranged by size and grouped into homologous pairs.
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Tests to Examine Chromosomes Amniocentesis - a needle is used to withdraw fluid from the uterus which contains fetal cells Chorionic Villi Sampling - a suction tube inserted into the vagina removes fetal cells *Tests are not usually performed due to risk of spontaneous abortion. |
Occasionally, errors occur during cell division that result in the offspring receiving too many or too few chromosomes (euploidy)
Polyploidy
- three or more complete sets of chromosomes. common in plants
Aneuploidy - when an organism has more or less than the normal (monosomy / trisomy)
Down's Syndrome ( Trisomy #21)
- mental retardation
- short stature, round face
- more likely in women over 40
- retardation is now known to be caused the the GART gene
Other Syndromes - Turner (XO), Klinefelter (XXY), Edward (Trisomy 13), Supermale (XYY), Poly-X Females (XXX)
Chromosome Mutations
Inversion (B)
Deletion (A)
Duplication (D)
Translocation (C)
Williams Syndrome - deletion
on chromosome 7
Cri du Chat Syndrome - deletion on chromosome 5
