A karyotype is an organized profile of a person’s chromosomes.

Chromosomes are arranged and numbered according to:

size, from largest to smallest

banding pattern, size and location of Giesma bands

centromere location, appear as a constriction

This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder.

Karyotype analyses are performed over 400,000 times per year in the U.S. and Canada.

How a karyotype is made:

1. Cells are blocked during mitosis.

2. The chromosomes are taken from those cells, attached to a slide and are stained with Giesma dye (pronounced Jeem-suh).  The dye stains regions of chromosomes that are rich in the base pairs Adenine (A) and Thymine (T) producing a dark band.

3. Pictures of the chromosomes are taken, cut out and matched up according to size, banding pattern and centromere position as guides.

Interpreting a karyotype:

Scientists use a specific notation to characterize the karyotype.

This notation includes:

i) the total number of chromosomes

ii) the sex chromosomes

iii) any extra or missing autosomal chromosomes

For example,         

47, XY, +18 indicates that the patient has 47 chromosomes, is a male, and has an extra autosomal chromosome 18.

46, XX is a female with a normal number of chromosomes

47, XXY is a patient with an extra sex chromosome.

Making a diagnosis with a karyotype:

Scientists can diagnose or predict genetic disorders by looking at the chromosomes in a karyotype.

Karyotype analysis is used in prenatal testing and in diagnosing certain disorders, such as Down syndrome.

Some chromosome aberrations in humans:

Chromosome abnormalitySyndrome name (condition)Effects on individual (variable)
XTurner’s●sterile female

●underdeveloped female characteristics

●short stature

●sometimes below normal intelligence

XXYKlinefelter’s●sterile male

●abnormal male characteristics

●abnormally long arms and legs

●below normal intelligence

Trisomy #21Down’s●low mental ability

●short arms and legs

●internal defects

●distinct facial features

Trisomy #18Edwards●severe abnormalities

●life expectancy about 10 weeks

Trisomy #13Patans●severe defects including small, non-functioning eyes

●survive only a few weeks after birth

Defective #5 (part of chromosome missing)Cri du chat●severe defects, both physical and mental

●sound, when crying, similar to a cat’s meow

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