| Term | Definition | |------|------------| | Mutation | A permanent alteration in the DNA sequence. | | DNA Replication | The biological process of producing two identical replicas of DNA from one original DNA molecule. | | DNA Polymerase | An enzyme crucial for DNA replication that synthesizes DNA molecules by adding nucleotides to the 3' end of a DNA strand. It also possesses proofreading capabilities to correct errors. | | Mispairing of Bases | An error during DNA replication where an incorrect nucleotide is incorporated into the new DNA strand, often due to the flexible nature of DNA bases or tautomeric shifts. | | Tautomers | Rare chemical forms of DNA bases that can hydrogen bond with the wrong complementary base, leading to mispairing during replication. | | Strand-Slippage | An error during DNA replication where the DNA polymerase either adds an extra base or omits a base, particularly common in repetitive DNA sequences. | | Depurination | A chemical reaction where a purine base (adenine or guanine) is spontaneously removed from the DNA backbone by hydrolysis, leaving a gap. | | Deamination | A chemical reaction where an amine group is removed from a base, such as cytosine, converting it into uracil, which can lead to mismatch pairing. | | Ultraviolet Radiation | Electromagnetic radiation from the sun that can damage DNA, most notably by causing covalent bonds between adjacent thymine bases, forming thymidine dimers. | | Thymidine Dimer | A covalent bond formed between two adjacent thymine bases on a DNA strand due to exposure to UV radiation, distorting the DNA helix and hindering replication. | | Mismatch Repair System | A cellular mechanism that corrects errors, such as mispaired bases, that escape the proofreading activity of DNA polymerase during replication. | | DNA Ligase | An enzyme that joins DNA fragments by catalyzing the formation of phosphodiester bonds, essential for sealing the DNA backbone after repair. | | Point Mutation | A mutation that affects a single nucleotide base pair, typically involving the substitution of one base for another. | | Transition | A type of point mutation where a purine base is replaced by another purine (adenine to guanine or vice versa), or a pyrimidine is replaced by another pyrimidine (cytosine to thymine or vice versa). | | Transversion | A type of point mutation where a purine base is replaced by a pyrimidine, or vice versa (e.g., adenine to thymine). | | Untranslated Regions (UTRs) | Regions of a gene’s mRNA that are transcribed but not translated into protein. Mutations here are often silent. | | Exons | The segments of a gene's DNA or mRNA that are translated into proteins. | | Splice Sites | Nucleotide sequences at the boundaries between introns and exons that are recognized by the splicing machinery to remove introns from pre-mRNA. | | Missense Mutation | A point mutation that results in a codon change leading to the substitution of one amino acid for another in the protein sequence. | | Nonsense Mutation | A point mutation that changes a codon specifying an amino acid into a premature stop codon, leading to a truncated protein. | | Frameshift Mutation | A mutation caused by the insertion or deletion of nucleotides in a number not divisible by three, altering the reading frame of the genetic code and changing all subsequent amino acids. | | Single Nucleotide Polymorphism (SNP) | A variation in a single nucleotide base at a specific position in the genome, occurring in at least 1% of the population. | | Microsatellites | Short, repetitive sequences of DNA, typically 2-6 base pairs long, that are tandemly repeated. | | Minisatellites | Longer repetitive sequences of DNA, typically 10-60 base pairs long, that are tandemly repeated. | | Genome Variant | Any difference in DNA sequence among individuals, ranging from single nucleotide changes to large chromosomal alterations. | | Pathogenic Mutation | A mutation that disrupts the normal function of a gene and can lead to disease. | | Coding Regions | The parts of a gene that are transcribed into mRNA and subsequently translated into proteins. | | Non-coding Regions | DNA sequences that are not transcribed into protein, including regulatory elements and intergenic regions. | | Reactive Oxygen Species (ROS) | Highly reactive molecules containing oxygen that can damage cellular components, including DNA. | | Methylation at CpG | The addition of a methyl group to a cytosine base in a CpG dinucleotide sequence, an epigenetic modification often associated with gene silencing. | | CpG Islands | Regions of DNA that are enriched in CpG dinucleotides, often found in gene promoter regions. | | Germline Mutations | Mutations that occur in egg or sperm cells and are therefore heritable by offspring. | | Somatic Mutations | Mutations that occur in non-germline cells and are not inherited by offspring; they are confined to the affected individual. | | Silent Mutation | A mutation that alters the DNA sequence but does not change the amino acid sequence of the resulting protein, often due to redundancy in the genetic code. | | Conservative Change | An amino acid substitution where the new amino acid has similar chemical properties to the original one, usually resulting in a minor impact on protein function. | | Non-Conservative Change | An amino acid substitution where the new amino acid has significantly different chemical properties from the original one, potentially drastically altering protein structure and function. | | Splice Site Mutation | A mutation occurring at the boundary between an intron and an exon, interfering with the proper splicing of pre-mRNA. | | Copy Number Variants (CNVs) | Variations in the number of copies of a particular DNA segment, ranging in size from a few kilobases to millions of base pairs. | | Genomics | The study of the entire set of genes in an organism (the genome), including their interactions with each other and the environment. | | DNA Sequencing | A laboratory technique used to determine the exact order of nucleotides within a DNA molecule. | | Mendelian Diseases | Genetic disorders caused by mutations in a single gene, typically inherited in a predictable pattern (e.g., autosomal dominant, autosomal recessive). | | Multifactorial Diseases | Diseases that result from the combined effects of multiple genes and environmental factors. | | Precision Medicine | A medical approach that tailors disease prevention and treatment strategies to individuals based on their genetic makeup, lifestyle, and environment. | | Unifactorial Disease | A disease caused by a single factor, such as a mutation in a single gene. | | Phenotype | The observable physical or biochemical characteristics of an organism, determined by its genotype and environmental influences. | | Genotype | The genetic makeup of an organism, specifically the alleles present at a particular locus or for a set of genes. | | Allele | One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. | | Autosomal Dominant | A mode of inheritance where a disease or trait is caused by a mutation in one copy of a gene located on an autosome (non-sex chromosome), and only one copy is needed to express the trait. | | Autosomal Recessive | A mode of inheritance where a disease or trait is caused by a mutation in both copies of a gene located on an autosome, and two mutated copies are required for the trait to be expressed. | | X-Linked Disorders | Genetic disorders caused by mutations in genes located on the X chromosome. | | Carrier | An individual who possesses one copy of a recessive allele and can transmit it to their offspring, but typically does not express the trait themselves. | | Penetrance | The proportion of individuals with a particular genotype who exhibit the expected phenotype. | | Incomplete Penetrance | A situation where individuals with a specific genotype do not always express the corresponding phenotype. | | Anticipation | A phenomenon where a genetic disorder appears at an earlier age and/or with greater severity in successive generations, often associated with unstable repeat expansions. | | Mosaicism | The presence of two or more genetically distinct cell lines within a single individual, all derived from a single fertilized egg. | | Haploinsufficiency | A condition where having only one functional copy of a gene (instead of two) is insufficient to maintain normal function, leading to a phenotype. | | Consanguinity | The state of being descended from the same ancestor; marriage or breeding between closely related individuals. | | X-Inactivation | The process in female mammals where one of the two X chromosomes is randomly inactivated early in development to equalize gene dosage between sexes. | | X-Linked Dominance | A mode of inheritance where a mutation on the X chromosome is sufficient to cause a disorder, and it is expressed in both males and females who carry the mutation. | | Mitochondrial Inheritance | Inheritance of genetic material located in the mitochondria, which is passed down exclusively from the mother to all her offspring. | | Oxidative Phosphorylation | The metabolic pathway in mitochondria that generates ATP, the main energy currency of the cell, through a series of redox reactions. | | Meiosis | A type of cell division that reduces the number of chromosomes by half, producing gametes (sperm and egg cells) for sexual reproduction. | | Independent Assortment | The random orientation of homologous chromosome pairs at the metaphase plate during meiosis I, leading to diverse combinations of maternal and paternal chromosomes in the gametes. | | Crossing Over (Recombination) | The exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis I, creating new combinations of alleles. | | Tetrad | A pair of homologous chromosomes, each consisting of two sister chromatids, that are paired up during prophase I of meiosis. | | Chiasmata | The visible points of contact between non-sister chromatids where crossing over has occurred during meiosis. | | Spermatogenesis | The process of producing mature sperm cells from spermatogonia. | | Oogenesis | The process of producing mature egg cells (ova) from oogonia. | | Oocyte | An immature female reproductive cell that has the potential to develop into an ovum after fertilization. | | Polar Bodies | Small cells produced during meiosis in females that contain excess chromosomes but little cytoplasm; they are non-functional. | | Chromosome Abnormalities | Any deviation from the normal number or structure of chromosomes. | | Constitutional Abnormality | A chromosome abnormality present in all cells of an individual, originating from the germline or early embryonic development. | | Somatic Abnormality | A chromosome abnormality that occurs in somatic cells after fertilization and is confined to certain tissues or cells. | | Karyotype | The complete set of chromosomes in a cell or organism, arranged in homologous pairs and ordered by size and shape. | | Aneuploidy | The condition of having an abnormal number of chromosomes, such as an extra chromosome (trisomy) or a missing chromosome (monosomy). | | Polyploidy | The condition of having more than two complete sets of chromosomes (e.g., triploidy, tetraploidy). | | Trisomy | A type of aneuploidy where there are three copies of a particular chromosome instead of the usual two. | | Monosomy | A type of aneuploidy where there is only one copy of a particular chromosome instead of the usual two. | | Non-disjunction | The failure of homologous chromosomes or sister chromatids to separate properly during meiosis, leading to aneuploidy. | | Trisomy 21 (Down Syndrome) | A genetic disorder caused by the presence of an extra copy of chromosome 21, characterized by intellectual disability and characteristic physical features. | | Klinefelter Syndrome (XXY) | A chromosomal disorder in males characterized by the presence of an extra X chromosome, often leading to infertility and sometimes developmental delays. | | Turner Syndrome (X) | A chromosomal disorder affecting females, characterized by the absence of one X chromosome, leading to short stature, infertility, and other physical characteristics. | | Trisomy X (XXX) | A chromosomal condition in females where there are three X chromosomes, often with minimal or no noticeable effects. | | Jacob’s Syndrome (XYY) | A chromosomal condition in males characterized by the presence of an extra Y chromosome, often associated with increased height. | | Translocation | A type of chromosomal abnormality where a segment of one chromosome breaks off and attaches to another chromosome. | | Reciprocal Translocation | A type of translocation where segments of two non-homologous chromosomes are exchanged. | | Robertsonian Translocation | A specific type of translocation that occurs between two acrocentric chromosomes (chromosomes with centromeres near their ends), involving the fusion of their long arms. | | Chromosomal Deletion | A type of chromosomal abnormality where a segment of a chromosome is lost. | | Ring Chromosome | A type of chromosomal abnormality where a chromosome breaks at both ends and the ends fuse to form a ring. | | Marker Chromosome | A small, structurally abnormal chromosome of unknown origin that cannot be identified by standard banding techniques. | | Unbalanced Translocation | A translocation where there is a net gain or loss of genetic material. | | Acrocentric Chromosome | A chromosome with a centromere located very close to one of its ends. | | Chronic Myeloid Leukaemia (CML) | A type of cancer of the blood and bone marrow characterized by the uncontrolled proliferation of myeloid cells, often associated with the BCR-ABL fusion gene. |