Template:Genetic Terms

From Embryology
Genetic Terms (expand to view) 
genetic abnormalities | Molecular Development | meiosis | mitosis
  • Alpha-Fetoprotein test (APF test) A prenatal test to measure the amount of a fetal protein in the mother's blood (or amniotic fluid). Abnormal amounts of the protein may indicate genetic or developmental problems in the fetus. Serum alpha-fetoprotein (AFP) is a fetal glycoprotein produced by the yolk sac and fetal liver. Low levels of AFP normally occur in the blood of a pregnant woman, high levels may indicate neural tube defects (spina bifida, anencephaly). (More? Alpha-Fetoprotein)
  • anaphase B - Cell division term referring to the part of anaphase during which the poles of the mitotic spindle move apart. (More? mitosis)
  • antisense - a sequence of DNA that is complementary usually to coding sequence of DNA or mRNA. Has been used experimentally to perturb or block gene expression. Also a mechanism that has been found to occur naturally as a regulatory mechanism.
  • aneuploidy - Genetic term used to describe an abnormal number of chromosomes mainly (90%) due to chromosome malsegregation mechanisms in maternal meiosis I.
  • autosomal inheritance - some hereditary diseases are described as autosomal which means that the disease is due to a DNA error in one of the 22 pairs that are not sex chromosomes. Both boys and girls can then inherit this error. If the error is in a sex chromosome, the inheritance is said to be sex-linked.
  • base - another term for nucleotide (usually a t c g).
  • base pair - Double stranded DNA has nucleotides A-T, C-G, paired by hydrogen bonds (2 for AT, 3 for GC). Note this means that GC is harder to separate that AT.
  • cis-acting elements - DNA sequences that through transcription factors or other trans-acting elements or factors, regulate the expression of genes on the same chromosome.
  • cohesin - a multi-protein subunit complex required to keep the sister chromatids together until their separation at anaphase (both in mitosis and meiosis), can also form rings that connect two DNA segments.
  • copy number variation - (copy number variants,CNVs) a DNA segment of one kilobase (kb) or larger that is present at a variable copy number in comparison with a reference genome. (More? Nature)
  • disomy - Genetic term referring to the presence of two chromosomes of a homologous pair in a cell, as in diploid. See chromosomal number genetic disorders uniparental disomy and aneuploidy. Humans have pairs usually formed by one chromosome from each parent.
  • DNMT - DNA methyltransferase.
  • DNA - DeoxyriboNucleic Acid. The genetic material found in mammalian chromosomes and mitochondria. Consisting of 4 nucleic acids (ATCG) that combine in a triptych (3 nucleotide codon) code for protein amino acids (3nt = 1aa).
  • DNA duplex - double stranded base-paired DNA forming a helix.
  • dominant inheritance - With autosomal dominant inheritance, there is an error in one of the 22 chromosome pairs. But the damaged gene dominates over the normal gene received from the other parent. If one of the parents has a disease caused by an autosomal dominant gene, all the children will have a 50 per cent risk of inheriting the dominant gene and a 50 per cent chance of not inheriting it. The children who do not inherit the damaged dominant gene will not themselves suffer from the disease, nor will they be able to pass the gene on to future children. This type of inheritance is present for example in Huntington's disease.
  • Down Syndrome - The historic name used for Trisomy 21, named after the original identifier Down, J.L.H. in a 1866 paper (cited above).
  • enhancer - A cis-regulatory sequence that can regulate levels of transcription from an adjacent promoter. Many tissue-specific enhancers can determine spatial patterns of gene expression in higher eukaryotes. Enhancers can act on promoters over many tens of kilobases of DNA and can be 5' or 3' to the promoter they regulate.
  • exon - a block of protein encoding sequence of DNA in a gene. Many proteins are made of several exons "stitched" or spliced together by editing out non-coding (intron) sequences.
  • fasta - a format for listing DNA sequence, where the first line has descritive information followed on the next line by the sequence without numbering.
  • GC repeat - a string of GC sequence repeated several times. Also associated with GC expansion, a mutational process that may lead eventually to serious gene expression effects.
  • gene - a sequence of DNA that encodes an individual protein.
  • genetic code - the 3 nucleotide sequence that forms a codon for a single amino acid or stop. See the gene code.
  • genome - the complete genetic information in the form of DNA available to a specific species.
  • hairpin loop - a folding of RNA generated by base pairing making a "===()" structure, the end loop and or stem of this structure can then interact with proteins or other RNA.
  • heteroplasmy - within a cell when more than one type of mitochondrial DNA (mtDNA) genome exists within the mitochondrion, or between mitochondria. Heteroplasmy can generate a pathogenic mutation, for example transfer RNA leucine (tRNALeu(UUR)) 3243A > G mutant can result in diabetes.
  • HyperD - hypermethylated domain has a role in regulating gene expression and epigenomics. The early embryo has large alterations in methylation patterns and DNA modification. (More? PMID 1943996)
  • HypoD - hypomethylated domain has a role in regulating gene expression and epigenomics. The early embryo has large alterations in methylation patterns and DNA modification. (More? PMID 1943996)
  • igDMR - imprinted germline differentially methylated regions
  • intron - a block of DNA within a gene not encoding a protein. Edited, spliced, out during transcription into mRNA. Originally thought not to contain any information, but more and more this appears not to be the case. Some intron sequences have been shown to regulate gene expression during development (eg c elegans, Lin 14)
  • karyotype - [Greek, karyon = kernel or nucleus + typos= stamp] The chromosomal makeup of a cell. Karyotyping describes the clinical genetic test.
  • meiosis I (MI) The first part of meiosis resulting in separation of homologous chromosomes, in humans producing two haploid cells (N chromosomes, 23), a reductional division.
Meiosis I: Prophase I - Metaphase I - Anaphase I - Telophase I
  • meiosis II - (MII) The second part of meiosis. In male human spermatogenesis, producing of four haploid cells (23 chromosomes, 1N) from the two haploid cells (23 chromosomes, 1N), each of the chromosomes consisting of two sister chromatids produced in meiosis I. In female human oogenesis, only a single haploid cell (23 chromosomes, 1N) is produced. Meiosis II: Prophase II - Metaphase II - Anaphase II - Telophase II
  • mosaic autosome monosomy - genetic abnormality caused by embryonic fusion or loss of an autosome early in embryonic development, resulting in a subset of cells in the body having only one of a pair of autosomes.  ICD-11 LD43.1 Mosaic monosomy of autosome
  • mRNA - messenger, transcribed from DNA in the nucleus and in mitochondria. Is translated by the ribosome in the cytoplasm (or mitochondrial matrix). Intermediate step in gene expression. (DNA-> mRNA-> protein).
  • mutation - any process which results in the alteration of the DNA sequence. Some conservative mutations may have no effect on the final amino acid encoded.
  • ncRNA - non-coding RNA.
  • nuchal translucency - (fetal nuchal-translucency thickness) An initial Trisomy 21 diagnostic ultrasound measurement in the fetal neck region carried out by trans-abdominal ultrasound at gestational age GA 10–14 weeks. Fetal sagittal section scan at a magnification that the fetus occupied at least 75% of the image. Measured is the maximum thickness of the subcutaneous translucency between the skin and the soft tissue overlying the cervical spine.
  • Philadelphia chromosome - (Philadelphia translocation) Genetic term referring to a chromosomal abnormality resulting from a reciprocal translocation between chromosome 9 and 22 (t(9;22)(q34;q11)). This is associated with the disease chronic myelogenous leukemia (CML).
  • ploidy - refers to the chromosomal genetic content of cells.
  • promoter - A regulatory region a short distance upstream from the 5' end of a transcription start site that acts as the binding site for RNA polymerase II. A region of DNA to which RNA polymerase IIbinds in order to initiate transcription.
  • point mutation - a change in a single nucleotide.
  • recessive inheritance - With autosomal recessive inheritance, the diseased individual has inherited the same gene damage from both father and mother. The damage is found on both chromosomes in the pair. But as this is not ´dominant gene damageª, neither father nor mother show any sign of disease, they are healthy carriers of the gene. We are all carriers of about five recessive genes of this type, but as spouses are seldom carriers of exactly the same damaged gene(s), all will probably go well in the next generation.
  • regulatory sequence - (regulatory region, regulatory area) is a segment of DNA where regulatory proteins such as transcription factors bind preferentially.
  • ribosome - complex of rRNA and ribosomal proteins, bind mRNA and translate it into protein.
  • RNA - RiboNucleic Acid. The intermediate nucleic acid involved in gene expression. It comes in 3 forms: tRNA, mRNA, rRNA.
  • rRNA - ribosomal, translates mRNA into protein. rRNA provides the "scaffolding" on which many ribosomal proteins are assembled as 2 subunits that themselves assemble to form a ribosome. rRNA genes are localized to the nucleolus in the nucleus, a sometimes visible region of DNA usually constantly being transcribed.
  • segmental aneuploidies - generated when a small piece of a chromosome is gained or lost during cell division, resulting in subchromosomal copy number (CN) changes.
  • single umbilical artery - (SUA) Placental cord with only a single placental artery (normally paired). This abnormality can be detected by ultrasound (colour flow imaging of the fetal pelvis) and is used as an indicator for further prenatal diagnostic testing for chromosomal abnormalities and other systemic defects. (More? Prenatal Diagnosis | Ultrasound)
  • telophase - Cell division term referring to the fifth mitotic stage, where the vesicles of the nuclear envelope reform around the daughter cells, the nucleoli reappear and the chromosomes unfold to allow gene expression to begin. This phase overlaps with cytokinesis, the division of the cell cytoplasm.
  • telomere - regions at the end of chromosomes. Shortening of the telomeres is thought to be associated with cellular aging. The enzyme that maintains the telomere is called telomerase. Introducing this gene into a cell can extend the cells lifespan.
  • topologically associating domain - (TAD) a self-interacting genomic region, DNA sequences within a TAD physically interact with each other more frequently than with sequences outside the TAD.
  • transcription factor - a protein which binds to DNA activating (usually) gene expression. There are many different ways and forms that this activation can take place, but most transcription factors fall into specific classes (eg zinc fingers, helix loop helix).
  • triple markers - alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol. ))trisomy 21}}
  • triploidy - genetic abnormality caused by one additional set of chromosomes, for a total of 69 chromosomes. Maternally present with albuminuria, edema, or hypertension. Extra maternally inherited chromosomes, microcephaly and an enlarged placenta that is enlarged and filled with cysts. Extra paternally inherited chromosomes, severe growth problems, enlarged head, and a small placenta. Non-mosaic triploidy is highly lethal, and is rarely observed in live births.  ICD-11 LD42.0 Triploidy
  • trisomy mosaicism - a rare chromosome disorder characterized by having an extra copy of a chromosome in a proportion, but not all, of a person’s cells.
  • tRNA - transfer, binds single amino acids acts as a "donor' for protein synthesis.
  • uniparental disomy - Genetic term referring to cells containing both copies of a homologous pair of chromosomes from one parent and none from the other parent.
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