A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points along each chromosome which enable a pair of chromosomes to align correctly with each other before separating during meiosis. This is the basis for Mendelian inheritance which characterizes inheritance patterns of genetic material from an organism to its offspring parent developmental cell at the given time and area.
Gene duplication is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene. Gene duplications can arise as products of several types of errors in DNA replication and repair machinery as well as through fortuitous capture by selfish genetic elements. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage.
Comparative genomic hybridization(CGH) is a molecular cytogenetic method for analysing copy number variations (CNVs) relative to ploidy level in the DNA of a test sample compared to a reference sample, without the need for culturing cells. The aim of this technique is to quickly and efficiently compare two genomic DNA samples arising from two sources, which are most often closely related, because it is suspected that they contain differences in terms of either gains or losses of either whole chromosomes or subchromosomal regions (a portion of a whole chromosome). This technique was originally developed for the evaluation of the differences between the chromosomal complements of solid tumor and normal tissue, and has an improved resolution of 5–10 megabases compared to the more traditional cytogenetic analysis techniques of giemsa banding and fluorescence in situ hybridization (FISH) which are limited by the resolution of the microscope utilized.
Genetics, a discipline of biology, is the science of heredity and variation in living organisms.
Haploinsufficiency in genetics describes a model of dominant gene action in diploid organisms, in which a single copy of the wild-type allele at a locus in heterozygous combination with a variant allele is insufficient to produce the wild-type phenotype. Haploinsufficiency may arise from a de novo or inherited loss-of-function mutation in the variant allele, such that it yields little or no gene product. Although the other, standard allele still produces the standard amount of product, the total product is insufficient to produce the standard phenotype. This heterozygous genotype may result in a non- or sub-standard, deleterious, and (or) disease phenotype. Haploinsufficiency is the standard explanation for dominant deleterious alleles.
An isochromosome is an unbalanced structural abnormality in which the arms of the chromosome are mirror images of each other. The chromosome consists of two copies of either the long (q) arm or the short (p) arm because isochromosome formation is equivalent to a simultaneous duplication and deletion of genetic material. Consequently, there is partial trisomy of the genes present in the isochromosome and partial monosomy of the genes in the lost arm.
Subtelomeres are segments of DNA between telomeric caps and chromatin.
A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where there is an atypical number of chromosomes, or as structural abnormalities, where one or more individual chromosomes are altered. Chromosome mutation was formerly used in a strict sense to mean a change in a chromosomal segment, involving more than one gene. Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. Chromosome abnormalities may be detected or confirmed by comparing an individual's karyotype, or full set of chromosomes, to a typical karyotype for the species via genetic testing.
The Olduvai domain, known until 2018 as DUF1220 and the NBPF repeat, is a protein domain that shows a striking human lineage-specific (HLS) increase in copy number and appears to be involved in human brain evolution. The protein domain has also been linked to several neurogenetic disorders such as schizophrenia and increased severity of autism. In 2018, it was named by its discoverers after Olduvai Gorge in Tanzania, one of the most important archaeological sites for early humans, to reflect data indicating its role in human brain size and evolution.
Low copy repeats (LCRs), also known as segmental duplications (SDs), are DNA sequences present in multiple locations within a genome that share high levels of sequence identity.
8p23.1 duplication syndrome is a rare genetic disorder caused by a duplication of a region from human chromosome 8. This duplication syndrome has an estimated prevalence of 1 in 64,000 births and is the reciprocal of the 8p23.1 deletion syndrome. The 8p23.1 duplication is associated with a variable phenotype including one or more of speech delay, developmental delay, mild dysmorphism, with prominent forehead and arched eyebrows, and congenital heart disease (CHD).
Non-allelic homologous recombination (NAHR) is a form of homologous recombination that occurs between two lengths of DNA that have high sequence similarity, but are not alleles.
1q21.1 deletion syndrome is a rare aberration of chromosome 1. A human cell has one pair of identical chromosomes on chromosome 1. With the 1q21.1 deletion syndrome, one chromosome of the pair is not complete, because a part of the sequence of the chromosome is missing. One chromosome has the normal length and the other is too short.
1q21.1 duplication syndrome or 1q21.1 (recurrent) microduplication is a rare aberration of chromosome 1.
Stephen Wayne "Steve" Scherer is a Canadian scientist who studies genetic variation in human disease. He obtained his PhD at the University of Toronto under Professor Lap-chee Tsui. Together they founded Canada's first human genome centre, the Centre for Applied Genomics (TCAG) at the Hospital for Sick Children. He continues to serve as director of TCAG, and is also a University Professor in the Department of Molecular Genetics, and the director of the McLaughlin Centre at the Temerty Faculty of Medicine at the University of Toronto.
Genomic structural variation is the variation in structure of an organism's chromosome. It consists of many kinds of variation in the genome of one species, and usually includes microscopic and submicroscopic types, such as deletions, duplications, copy-number variants, insertions, inversions and translocations. Originally, a structure variation affects a sequence length about 1kb to 3Mb, which is larger than SNPs and smaller than chromosome abnormality. However, the operational range of structural variants has widened to include events > 50bp. The definition of structural variation does not imply anything about frequency or phenotypical effects. Many structural variants are associated with genetic diseases, however many are not. Recent research about SVs indicates that SVs are more difficult to detect than SNPs. Approximately 13% of the human genome is defined as structurally variant in the normal population, and there are at least 240 genes that exist as homozygous deletion polymorphisms in human populations, suggesting these genes are dispensable in humans. Rapidly accumulating evidence indicates that structural variations can comprise millions of nucleotides of heterogeneity within every genome, and are likely to make an important contribution to human diversity and disease susceptibility.
22q11.2 distal deletion syndrome is a rare genetic condition caused by a tiny missing part of one of the body's 46 chromosomes – chromosome 22. 22q11.2 distal deletion syndrome appears to be a recurrent genomic disorder distinct from 22q11.2 deletion syndrome also known as DiGeorge syndrome and velocardiofacial syndrome.
Chromosomal deletion syndromes result from deletion of parts of chromosomes. Depending on the location, size, and whom the deletion is inherited from, there are a few known different variations of chromosome deletions. Chromosomal deletion syndromes typically involve larger deletions that are visible using karyotyping techniques. Smaller deletions result in Microdeletion syndrome, which are detected using fluorescence in situ hybridization (FISH)
Structural variation in the human genome is operationally defined as genomic alterations, varying between individuals, that involve DNA segments larger than 1 kilo base (kb), and could be either microscopic or submicroscopic. This definition distinguishes them from smaller variants that are less than 1 kb in size such as short deletions, insertions, and single nucleotide variants.
Human somatic variations are somatic mutations both at early stages of development and in adult cells. These variations can lead either to pathogenic phenotypes or not, even if their function in healthy conditions is not completely clear yet.
