Cell Physiology : Glossary
Aneuploidy: Any chromosome number that is not an exact multiple of the haploid number. In humans, where 23 chromosomes are found in sperm and eggs, an individual with 46 chromosomes is "euploid" but an individual with only one X chromosome (Turner syndrome) has only 45 chromosomes and is "aneuploid."
Antisense transcript: An RNA molecule that is produced from the DNA strand opposite the one that encodes the gene product.
Autosomal transgene: A gene that has been artificially introduced (by microinjection of DNA into the nucleus or by using a viral vector) and integrated into any one of the chromosomes except the sex chromosomes.
Autosomes: In humans, all of the chromosomes except the sex chromosomes (the two X chromosomes in females or the X and Y in males).
Barr body: In female cells stained with certain dyes, a darkly staining mass that appears in the nucleus of cells in the interphase stage of the cell cycle. This mass corresponds to the inactive X chromosome.
Cytosine methylation of DNA: A covalent modification (the attachment of a methyl group to the 5-position of cytosine) of one of the four bases found in DNA. This modification is often found on cytosine residues when cytosine is followed immediately by guanine (CpG) but not when cytosine is followed by adenine or thymine.
Exons: Those portions of genes that are found in the mature mRNA (as opposed to "introns" which are the portions of the primary RNA transcript of a gene that are spliced out before the mRNA is transported from the nucleus to the cytoplasm). Most exons encode the amino sequences found in proteins but some exons (often all or part of the first and last exons of a gene) encode "untranslated" sequence found at the beginning and end of many mRNAs.
Gene conversion: The process of "converting" allele "A" at a locus into allele "B" by using allele "B" as a template in a DNA repair synthesis process at allele "A." If such a gene conversion event occurs during spermatogenesis, it will result in three sperm carrying the B allele and only one sperm carrying the A allele (rather than the expected two B sperm and two A sperm).
Histone: One of the proteins around which DNA is wrapped to form the basic building block of chromosomes.
Homologous recombination: The exchange of DNA sequences between pairs of chromosomes. For example, the distal portion of the maternally inherited X chromosome may exchange with the distal portion of the paternally inherited X chromosome during oogenesis so that a "hybrid" chromosome is formed. Any offspring inheriting such a recombined chromosome will receive X chromosome genes from both the maternal grandmother and maternal grandfather.
Intrachromosomal recombination: The exchange of DNA sequences within a chromosome, often mediated by sequences repeated in tandem or by inverted repeated sequences.
Isoform: Different products that may be produced from the same gene (by alternative splicing of mRNA in different tissues, for example) or different products produced from homologous genes on the X and Y chromosomes.
Orthologue: Genes or chromosomes of different species that are presumed to be homologous. For example, the human RPS4X is "homologous" to the human RPS4Y but human SRY is orthologous to mouse Sry.
Parental imprinting: The marking of chromosomes (by differential cytosine methylation or differential deposition or modification of chromosomal proteins) as maternal or paternal. It may result in some gene products being produced from only the maternally inherited or only the paternally inherited copy of some genes.
Ribosomes: The molecular "anvils" (composed of many different proteins and several RNAs) upon which proteins are synthesized from mRNAs.
Telomeric markers: Genetic variants of genes located near the ends of chromosomes.
Trophoblast: Cells that form part of the placenta, enabling the fetus to survive within the maternal uterus.
