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[5] [6] Aneuploidy can be full, involving a whole chromosome missing or added, or partial, where only part of a chromosome is missing or added. [5] Aneuploidy can occur with sex chromosomes or autosomes. [citation needed] Rather than having monosomy, or only one copy, the majority of aneuploid people have trisomy, or three copies of one chromosome.
Partial monosomy can occur in unbalanced translocations or deletions, in which only a portion of the chromosome is present in a single copy (see deletion (genetics)). Monosomy of the sex chromosomes (45,X) causes Turner syndrome. 2: Disomy: Disomy is the presence of two copies of a chromosome.
Polysomy of chromosomes 1, 2, 4, 5, and 25 are also frequently involved in canine tumors. [16] Chromosome 1 may contain a gene responsible for tumor development and lead to changes in the karyotype, including fusion of the centromere, or centric fusions. [16] Aneuploidy due to nondisjunction is a common feature in tumor cells. [17]
CIN often results in aneuploidy. There are three ways that aneuploidy can occur. It can occur due to loss of a whole chromosome, gain of a whole chromosome or rearrangement of partial chromosomes known as gross chromosomal rearrangements (GCR). All of these are hallmarks of some cancers. [13]
Turner syndrome is the only full monosomy that is seen in humans — all other cases of full monosomy are lethal and the individual will not survive development. Cri du chat syndrome – (French for "cry of the cat" after the persons' malformed larynx) a partial monosomy caused by a deletion of the end of the short arm of chromosome 5
The number of chromosomes in the cell where trisomy occurs is represented as, for example, 2n+1 if one chromosome shows trisomy, 2n+1+1 if two show trisomy, etc. [2] "Full trisomy", also called "primary trisomy", [2] means that an entire extra chromosome has been copied. "Partial trisomy" means that there is an extra copy of part of a chromosome.
It is the most common autosomal trisomy leading to miscarriage, and the second most common chromosomal cause (closely following X-chromosome monosomy). [2] About 6% of miscarriages have trisomy 16. [3] Those mostly occur between 8 and 15 weeks after the last menstrual period. [3]
Many organ systems are affected by triploidy, but the central nervous system and skeleton are the most severely affected: . Common central nervous system defects seen in triploidy include holoprosencephaly, hydrocephalus (increased amount of cerebrospinal fluid within the brain), ventriculomegaly, Arnold–Chiari malformation, agenesis of the corpus callosum and neural tube defects.