Reproductive Genetics : Gene Structure, Mutation, Molecular Tools, Types of Inheritance, Counseling Issues, Oncogenes - 27/08/11
Doi : 10.1016/B978-0-323-02951-3.50005-4
KEY TERMS AND DEFINITIONS
Allele. : One of the alternative versions of a gene that occupy a given locus (the physical location of a gene).
Centromere. : A region of a chromosome, forming a point at which the chromatids are held together during meiosis and mitosis. A primary constriction, the centromere, divides the chromosome into two “arms” designated p and q.
Chimerism. : The presence of two different cell populations derived from two separate conceptuses within the same individual. Acquired chimerism is a result of transplantation.
Chromatid. : A constituent strand of a chromosome seen in prophase, after division of the chromosomes.
Chromatid Break. : Separation in chromatin material in only one chromatid arm.
Chromosome. : Threadlike structures of chromatin containing genetic information (DNA) located in the cell nucleus.
Codon. : A sequence of 3 bases in a DNA molecule specifying the code for a specific amino acid.
Deletion. : The loss of a sequence of DNA of varying amounts from a chromosome.
Exon. : The coding region of a gene.
Expressivity. : The degree to which the features of a genetic defect is expressed.
Fragment. : A small piece of chromosome separated from its centromere.
Gene. : A unit of genetic information, a sequence of nucleotides that forms the code for the production of a functional product.
Genome. : A complete complement of genes in a gamete, an individual, a population, or a species.
Genotype. : The genetic make-up of an individual, the alleles at one locus.
Insertion. : A condition in which a segment of DNA from one chromosome is inserted into another chromosome.
Intron. : Noncoding region of a gene. A gene will have many introns intervening between the coding regions (exons).
Inversion. : A condition occurring when a chromosome suffers two breaks with a 180° rotation of the fragments. If the centromere is involved in the inversion, the condition is called a pericentric inversion. If the centromere is not included, it is called a paracentric inversion.
Isochromosome. : An abnormal chromosome that is produced by a transverse split instead of the usual longitudinal split of the centromere. The daughter chromosome formed will have either of the two identical arms while the other arm is missing.
Karyotype. : An arrangement of all the chromosomes of a cell at metaphase in descending order of size.
Locus. : The physical location of a gene on a chromosome. There may be alternative forms of the gene (alleles).
Mosaicism. : The presence of two or more genetically different cell types derived from a single zygote within the same individual. This is not to be confused with chimera, in which the different cell types in one individual are derived from two different zygotes.
Mutation. : A permanent and heritable alteration in DNA sequence.
Nondisjunction. : The failure of a pair of chromosomes to separate during meiosis or mitosis. In meiosis, if one daughter cell receives both members of the chromosome pair, after fertilization a triple number of the chromosome, or a trisomic state, exists in each cell.
Oncogene. : A gene that acts in a dominant fashion to unregulate cell growth and proliferation, resulting in tumor development.
Penetrance. : The fraction of individuals with a mutation that actually demonstrates any clinical features of the mutation. Generally refers to autosomal dominant conditions.
Phenotype. : The observed characteristics of a gene. This can be biochemical, physical, or physiological.
Pleiotropic. : Description of genes that have multiple diverse clinical effects on the affected individual.
Polymerase Chain Reaction (PCR). : The process by which a small segment of DNA may be amplified to produce larger amounts of materials for analysis.
Polymorphism. : Natural variations of a gene, DNA sequence, or chromosome that does not have adverse clinical consequence. Generally, the frequency of a polymorphism in the general population is at least 0.01 (1%) or greater than that which would occur by recurrent mutation alone.
Restriction Endonucleases. : Bacterial enzymes that recognize and cut specific nucleotide sequences in the double-stranded DNA molecule at specific sites.
Restriction Fragment Length Polymorphism (RFLP). : The study of DNA fragments produced by restriction endonucleases has demonstrated that normal individuals may have variations in the DNA sequences without the presence of an abnormality. RFLPs are generated using restriction endonucleases and can indirectly identify mutations in a gene that is near a polymorphic site.
Ribonucleic Acid (RNA). : A single-helix nuclear protein that serves several purposes in the cell. It is composed of a sugar (ribose), a phosphate, and a purine or pyrimidine base.
Translocation. : The transfer of a segment of chromosome material from one chromosome to another.
Centromere. : A region of a chromosome, forming a point at which the chromatids are held together during meiosis and mitosis. A primary constriction, the centromere, divides the chromosome into two “arms” designated p and q.
Chimerism. : The presence of two different cell populations derived from two separate conceptuses within the same individual. Acquired chimerism is a result of transplantation.
Chromatid. : A constituent strand of a chromosome seen in prophase, after division of the chromosomes.
Chromatid Break. : Separation in chromatin material in only one chromatid arm.
Chromosome. : Threadlike structures of chromatin containing genetic information (DNA) located in the cell nucleus.
Codon. : A sequence of 3 bases in a DNA molecule specifying the code for a specific amino acid.
Deletion. : The loss of a sequence of DNA of varying amounts from a chromosome.
Exon. : The coding region of a gene.
Expressivity. : The degree to which the features of a genetic defect is expressed.
Fragment. : A small piece of chromosome separated from its centromere.
Gene. : A unit of genetic information, a sequence of nucleotides that forms the code for the production of a functional product.
Genome. : A complete complement of genes in a gamete, an individual, a population, or a species.
Genotype. : The genetic make-up of an individual, the alleles at one locus.
Insertion. : A condition in which a segment of DNA from one chromosome is inserted into another chromosome.
Intron. : Noncoding region of a gene. A gene will have many introns intervening between the coding regions (exons).
Inversion. : A condition occurring when a chromosome suffers two breaks with a 180° rotation of the fragments. If the centromere is involved in the inversion, the condition is called a pericentric inversion. If the centromere is not included, it is called a paracentric inversion.
Isochromosome. : An abnormal chromosome that is produced by a transverse split instead of the usual longitudinal split of the centromere. The daughter chromosome formed will have either of the two identical arms while the other arm is missing.
Karyotype. : An arrangement of all the chromosomes of a cell at metaphase in descending order of size.
Locus. : The physical location of a gene on a chromosome. There may be alternative forms of the gene (alleles).
Mosaicism. : The presence of two or more genetically different cell types derived from a single zygote within the same individual. This is not to be confused with chimera, in which the different cell types in one individual are derived from two different zygotes.
Mutation. : A permanent and heritable alteration in DNA sequence.
Nondisjunction. : The failure of a pair of chromosomes to separate during meiosis or mitosis. In meiosis, if one daughter cell receives both members of the chromosome pair, after fertilization a triple number of the chromosome, or a trisomic state, exists in each cell.
Oncogene. : A gene that acts in a dominant fashion to unregulate cell growth and proliferation, resulting in tumor development.
Penetrance. : The fraction of individuals with a mutation that actually demonstrates any clinical features of the mutation. Generally refers to autosomal dominant conditions.
Phenotype. : The observed characteristics of a gene. This can be biochemical, physical, or physiological.
Pleiotropic. : Description of genes that have multiple diverse clinical effects on the affected individual.
Polymerase Chain Reaction (PCR). : The process by which a small segment of DNA may be amplified to produce larger amounts of materials for analysis.
Polymorphism. : Natural variations of a gene, DNA sequence, or chromosome that does not have adverse clinical consequence. Generally, the frequency of a polymorphism in the general population is at least 0.01 (1%) or greater than that which would occur by recurrent mutation alone.
Restriction Endonucleases. : Bacterial enzymes that recognize and cut specific nucleotide sequences in the double-stranded DNA molecule at specific sites.
Restriction Fragment Length Polymorphism (RFLP). : The study of DNA fragments produced by restriction endonucleases has demonstrated that normal individuals may have variations in the DNA sequences without the presence of an abnormality. RFLPs are generated using restriction endonucleases and can indirectly identify mutations in a gene that is near a polymorphic site.
Ribonucleic Acid (RNA). : A single-helix nuclear protein that serves several purposes in the cell. It is composed of a sugar (ribose), a phosphate, and a purine or pyrimidine base.
Translocation. : The transfer of a segment of chromosome material from one chromosome to another.
Plan
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Article précédent
- Fertilization and Embryogenesis : Meiosis, Fertilization, Implantation, Embryonic Development, Sexual Differentiation
- Edith Cheng, Vern L. Katz
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- Vern L. Katz
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