Genotype Specificity

Karyotypes of Chromosomal Disorders

http://www.kscience.co.uk/as/module2/dna_structure/DNA_files/History%20of%20DNA%20research.htm

Karyotypes

• Each individual is identified by a relatively unique combination of nucleotides found in long coiled strands of DNA organized as chromosomes found in a cell’s nucleus.

• The number and arrangement of chromosomes in an organism is characteristic of that organism, and can be represented as a karyotype, which derived by arranging the chromosomes in pairs by size.

• The karyotype can be used to show differences in genetic makeup (genotype), which determines the features that

person has (phenotype).

Normal Male Karyotype

Twenty-three pairs of chromosomes. Twenty two pairs are called autosomes, 1 pair is called the sex chromosomes ; XY in a male. Males are associated with secondary sexual characteristics – abundant facial hair, voice, others. Differences are also evident in the genitalia.

Normal Female Karyotype

Twenty-three of chromosome pairs as in the male, but sex chromosomes are represented by XX. Females also have different physical features from males. A Barr body is also present in cells of the female, representing an inactivated X chromosome.

Klinefelter's Syndrome Karyotype

Three sex chromosomes are associated with Klinefelter. These individuals are males with some development of breast tissue normally seen in females. Little body hair is present, and such person are typically tall, with or without evidence of mental retardation. Males with XXXY, XXXXY, and XXXXXY karyotypes have a more severe presentation, and mental retardation is expected.

Turner's Syndrome Karyotpye

Only 1 sex chromosome is present -X0, or X_. The expected Y chromosome is missing. Turner syndrome is associated with underdeveloped ovaries, short stature, webbed/bull neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics. Mental retardation typically not evident.

Down’s Syndrome Karyotype

Normally associated with 3 copies of chromosome number 21(trisomy of chromosome 21), rather than the 2 found normally. Down syndrome is characterized by differing degrees of mental retardation, a skin fold over the eye, typically short stature, and short hands with a deep crease in the palm.