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Different chromosomes are observed at different frequencies depending on the type of CPM observed. [2] The pregnancy outcome is strongly chromosome specific. The most frequently seen trisomic cells in confined placental mosaicism involve chromosomes 2, 3, 7, 8 and 16. The next frequently involved are 9, 13, 15, 18, 20 and 22. [8]
[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.
Aneuploidy is the state where one or more individual chromosomes of a normal set are absent or present in more than their usual number of copies (excluding the absence or presence of complete sets, which is considered euploidy). Unlike euploidy, aneuploid karyotypes will not be a multiple of the haploid number.
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.
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
Triploid fetuses have intrauterine growth restriction beginning early in the pregnancy, as early as 12 weeks, and does not affect the head as severely as the body. Oligohydramnios, low levels of amniotic fluid, is common in triploid pregnancies. Placental abnormalities are common in triploidy.
Aneuploidies is when a fetus retains an abnormal amount of haploid cells from their parents. However, both of these approaches have a high rate of false positive results of 2–7%. [9] If these tests indicate an increased risk of aneuploidy, then invasive diagnostic testing is used, such as amniocentesis or chorionic villus sampling.
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]