BT501 Quiz

Assignment no.02

Bt-501

Described known chromosomal disorders and then indicate type of chromosomal abnormalities and syndromes that arise each type of chromosomal disorders.

Chromosomal disorders:

A chromosome disorder results from a change in the number or structure of chromosomes. Each of our chromosomes? has a characteristic structure. Historically, scientists have used a staining technique that colours the chromosomes into a banding pattern. These banding patterns make each of our individual chromosomes easier to identify, like a map. A set of chromosomes, as seen under a microscope, is known as a karyotype?. Any deviation from the normal karyotype is known as a chromosome abnormality. While some chromosome abnormalities are harmless, some are associated with clinical disorders. Half of all spontaneous abortions are due to chromosome abnormalities.

Numerical abnormalities

The most severe chromosome disorders are caused by the loss or gain of whole chromosomes, which can affect hundreds, or even thousands, of genes? and are usually fatal. A few numerical abnormalities support development to term, either because the chromosome is small and/or contains relatively few genes or because there is a natural mechanism present to help adjust gene dosage. The major numerical abnormalities that survive to term are presented in Table 1, with Down’s syndrome? being the most common. The major numerical abnormalities that survive to term

Syndrome

Incidence

Down’s Trisomy 21 15 in 10,000

Edwards’ Trisomy 18 3 in 10,000

Patau’s Trisomy 13 2 in 10,000

Turner Monosomy X 2 in 10,000 (female births)

Klinefelter’s XXY 10 in 10,000 (male births)

XXX XXX 10 in 10,000 (female births)

XYY XYY 10 in 10,000 (male births)

Structural abnormalities

This is when large sections of DNA? are missing from or are added to a chromosome. Structural abnormalities can take several forms. Deletion: a mutation? causing part of the chromosome to be missing.

Duplication: a mutation causing part of the chromosome to be repeated, resulting in extra genetic material. Translocation: a mutation causing one portion of a chromosome to be moved to a different part of the chromosome (intrachromosomal) or to a different chromosome altogether (interchromosomal). There are two key types: o reciprocal: segments from two different chromosomes are exchanged o Robertsonian: an entire chromosome attaches to another.

Inversion: a mutation resulting in a portion of a chromosome being in the opposite orientation (inverted).

Ring: when a portion of a chromosome has broken off and formed a circle or ring.