Aneuploidy
Aneuploidy is a genetic condition characterized by an abnormal number of chromosomes in a cell, often resulting from errors in cell division. This can lead to developmental abnormalities and is associated with conditions such as Down syndrome and Turner syndrome. Aneuploidy can occur in both somatic cells and gametes, impacting the health and viability of an organism.
3 Key excerpts on "Aneuploidy"
eBook - ePub- Nessar Ahmed, Maureen Dawson, Chris Smith, Ed Wood(Authors)
- 2007(Publication Date)
- Taylor & Francis(Publisher)
...However, chromosomal mutations with numerical aberrations in the number of chromosomes present occur. These can be divided into two major types. Aneuploidy occurs when the number of chromosomes differs in having more or fewer than an exact multiple of the haploid number of chromosomes. Table 15.7 lists a number of human aneuploid abnormalities of autosomes and sex chromosomes. In contrast, euploidy is the presence of an exact multiple of the haploid number of chromosomes. Table 15.7 Aneuploid abnormalities of human chromosomes Aneuploidy Aneuploidy is usually caused by the nondisjunction of paired chromosomes at meiosis I or of sister chromatids at meiosis II or by delayed movement of a chromosome at anaphase. Nondisjunction is caused by the failure of pairs of homologues to separate or disjoin during segregation. Figure 15.31 (A) and (B) illustrates the consequences of nondisjunction during first meiosis and second meiosis for a single chromosome. Thus gametes are formed that either lack the chromosome or contain two copies of it. If these are fertilized by a normal haploid gamete, then zygotes are produced with one or three chromosomes. Thus nondisjunction can lead to a variety of aneuploid conditions. The loss of a single chromosome from an otherwise diploid genome is called monosomy (2N – 1). Nullisomy results from the loss of one pair of homologous chromosomes (2N – 2). The gain of one chromosome results in trisomy (2N + 1). Tetrasomy describes the presence of four copies of a specific chromosome rather than the normal two (2N + 2). Aneuploidy can also involve the loss or the addition of more than one particular chromosome or pair of chromosomes. Thus a double monosomy involves the loss of two separate nonhomologous chromosomes (2N – 1 – 1), while a double tetrasomy would describe the presence of four copies of two chromosomes (2N + 2 + 2)...
eBook - ePub- Chang-Hui Shen(Author)
- 2019(Publication Date)
- Academic Press(Publisher)
...The accuracy of SNPs can be limited by contamination and allele dropout. For the Aneuploidy screening, there was a false detection rate of 2.1% using SNP methods compared to 1% by traditional metaphase karyotyping. The SNP-based array approach with optimized protocols and parental support algorithms could be particularly suited to certain applications such as the PGD of single-gene defects and translocation chromosome imbalance combined with comprehensive detection of Aneuploidy. In translocation cases, normal embryos can be differentiated from balanced ones. Chromosomal Disorders: Numerical Chromosome Abnormalities Chromosomal disorders are caused by abnormalities in the number or the structure of chromosomes and cytogenetic karyotyping is a standard practice to identify all chromosomal disorders. Since an individual's phenotypes result from the expression of genes, the phenotype of a person with a chromosomal disorder can vary with the type of chromosomal defect. An abnormality in which the chromosome number is an exact multiple of the haploid number (n = 23) and is larger than the diploid number (n = 46) is called polyploidy. Polyploidy arises from fertilization of an egg by two sperm (total number of chromosomes increases to 69) or the failure in one of the divisions of either the egg or the sperm so that a diploid gamete is produced. The survival of such a fetus to full-term pregnancy is rare. Aneuploidy occurs when the chromosome number is not an exact multiple of the haploid number and results from the failure of paired chromosomes (at first meiosis) or sister chromatids (at second meiosis) to separate at anaphase. Thus, two cells are produced, one with a missing copy of a chromosome and one with an extra copy of that chromosome (Fig. 13.20). Fig...
eBook - ePubHandbook of Genetic Diagnostic Technologies in Reproductive Medicine
Improving Patient Success Rates and Infant Health
- Carlos Simón, Carmen Rubio, Carlos Simón, Carmen Rubio(Authors)
- 2022(Publication Date)
- CRC Press(Publisher)
...8 Aneuploidy in Human Oocytes and Preimplantation Embryos Eva R. Hoffmann DOI: 10.1201/9781003024941-8 Introduction A Historical Context for Human Aneuploidy After 30 years of widely held belief that humans had 48 chromosomes, the refinement of karyotyping techniques in the 1950s facilitated the discovery that humans have 46 chromosomes, including the XY sex chromosomes (1). Using improved cytogenetic techniques, Jacobs and Strong (1959) reported that Klinefelter Syndrome in males was caused by an extra X chromosome (2). In the same year, Jejeune, Gauthier, and Turpin (3, 4) and the Jacobs group (5) independently discovered that Down Syndrome was caused by an extra chromosome 21. Ford and colleagues (6) found that Turner Syndrome was caused by the loss of an X chromosome (45,X) in females and also reported the first mosaic individual (XXY/XX)(7). These studies reported in 1959 led to an explosion in the investigations into Aneuploidy (8 – 12) and initiated epidemiological and extensive cohort studies of both spontaneous miscarriages as well as live births (Figure 8.1). Of spontaneous miscarriages, nearly 50% are chromosomally abnormal, mainly due to Aneuploidy (one in three), but triploid conceptions are also common (13). To date, the most comprehensive cohort study is the US National Down Syndrome Project, which was initiated by Terry Hassold and Stephanie Sherman (14). FIGURE 8.1 Historical overview of developments in the importance and detection of Aneuploidy in human health. Abbreviations: SNP, single nucleotide polymorphisms; NGS, next generation sequencing; FISH, fluorescence in situ hybridization; array CGH, comparative genomic hybridization; qPCR, quantitative polymerase chain reaction; MeioMapping, recovery of both chromosome content and genetic variants (SNPs) from the same cell in oocytes and matched polar bodies. The population-based studies have revealed three important facets of human aneuploidies...
