Any condition in which the number of chromosomes differs from an exact multiple of the normal haploid number in a cell or organism. It commonly results from the gain or loss of individual chromosomes, but also can result from the duplication or deletion of part(s) of a chromosome or chromosomes.

Condition in which a cell or organism has two or more genetically distinct sets of chromosomes of the same species.

Condition in which a cell or organism has two or more genetically distinct sets of chromosomes that originate in different, though usually related, species.

A procedure in which a sample of amniotic sac fluid is withdrawn from the amniotic sac of a developing fetus and cells are cultured and examined for chromosomal abnormalities.

Technique for analyzing gene linkage and recombination in certain eukaryotic microorganisms (e.g., yeast, Neurospora, and Chlamydomonas) in which the four products of a single nucleus that has undergone meiosis are grouped together in a single structure. See also meiotic tetrad.

One of the three types of meiotic tetrads possible when two genes are segregating in a cross. The T tetrad contains two parental and two recombinant nuclei, one of each parental type and one of each recombinant type.

Two adjacent cell groups that differ in genotype and phenotype. They result from mitotic crossing-over within the somatic cells of a heterozygous individual

(a) A chromosomal mutation involving a change in the position of a chromosome segment (or segments) and the gene sequences it contains. (b) In polypeptide synthesis, translocation is the movement of the ribosome, one codon at a time, along the mRNA toward the 3? end.

A type of aneuploidy in which a normally diploid cell or organism possesses three copies of a particular chromosome instead of two copies. A trisomic cell is 2N +1.

A type of aneuploidy in which a normally diploid cell or organism possesses four copies of a particular chromosome instead of two copies. A tetrasomic cell is 2N + 2.

The presence of an extra copy of chromosome 21, which causes Down syndrome in humans.

The presence of an extra copy of chromosome 13, which causes Patau syndrome in humans.

The presence of an extra copy of chromosome 18, which causes Edwards syndrome in humans.

A bacterial cell that incorporates donor DNA received during conjugation into its genome.

transformation(a) In bacteria, a process in which genetic information is transferred by means of extracellular pieces of DNA. (b) In eukaryotes, the conversion of a normal cell with regulated growth properties to a cancer-like cell that can give rise to tumors.

In bacteria, a recombinant recipient cell generated by transduction.

A bacteriophage that is capable of following either the lytic cycle or lysogenic pathway. See also virulent phage.

Any bacteriophage that can mediate transfer of genetic material between bacteria by transduction.

Any enzyme that catalyzes the supercoiling of DNA.

The four haploid cells produced in a single meiosis. In some lower eukaryotes, these cells are contained within a common structure.

A genetic recombination that follows the rare pairing of homologous chromosomes during mitosis of a diploid cell. Also called mitotic recombination.

A type of aneuploidy in which one chromosome of a homologous pair is missing from a normally diploid cell or organism. A monosomic cell is 2N ? 1.

For a microorganism, a medium that contains the simplest set of ingredients (e.g., a sugar, some salts, and trace elements) required for the growth and reproduction of wild-type cells.

Condition in which a normally diploid cell or organism lacks one complete set of chromosomes.

A mutant strain of an organism that cannot synthesize a molecule required for growth and therefore must have the molecule supplied in the growth medium for it to grow. Also called auxotrophic mutant or nutritional mutant.

One of three types of meiotic tetrads possible when two genes are segregating in a cross. The PD tetrad contains four nuclei, all of which are parental genotypes, with two of one parent and two of the other parent.

Mechanism for formation of recombinant haploid cells that does not involve the regular alternation of meiosis and fertilization.

A special type of chromosome representing a bundle of numerous chromatids that have arisen by repeated cycles of replication of single chromatids without nuclear division. This type of chromosome is characteristic of various tissues of Diptera.

A chromosomal mutation in which a segment on one chromosome arm that does not include the centromere is inverted.

A gene that in normal cells functions to control the proliferation of cells and that when mutated can become an oncogene. See also tumor suppressor gene.

A change in the phenotypic effect of one or more genes as a result of a change in their position in the genome.

Condition in which a cell or organism has more than two sets of chromosomes.

A strain of an organism that is wild type for all nutritional requirements and can grow on minimal medium. See also auxotroph.

A phage that carries pieces of bacterial DNA between bacterial strains in the process of transduction

The progeny phages released after lysis of phage-infected bacteria.

A round, clear area in a lawn of bacteria on solid medium that results from the lysis of cells by repeated cycles of phage lytic growth.

Referring to genes or mutations that result in multiple phenotypic effects.

One of three types of meiotic tetrads possible when two genes are segregating in a cross. The NPD tetrad contains four nuclei, all of which have recombinant (nonparental) genotypes, that is, two of each possible type.

A type of aneuploidy in which one pair of homologous chromosomes is missing from a normally diploid cell or organism. A nullisomic cell is 2N ? 2.

An enzyme that catalyzes the degradation of a nucleic acid by breaking phosphodiester bonds.

Central region in a bacterial cell in which the chromosome is compacted.

A cell containing two nuclei with different genotypes produced by fusing cells from different sources.

A region of double-stranded DNA with different sequence information on the two strands.

Designation for an E. coli cell that has an F factor integrated into the bacterial chromosome. When a Hfr cell conjugates with a recipient (F?) cell, bacterial genes are transferred to the recipient with high frequency.

Chromatin that remains condensed throughout the cell cycle and is usually not transcribed. See also euchromatin.

One model of the molecular events in genetic recombination that involves an X-shaped intermediate visible in the electron microscope.

The lod (logarithm of odds) score method is a statistical analysis, usually performed by computer programs, based on data from pedigrees. It is used to test for linkage between two loci in humans.

Bacteriophage life cycle in which the phage takes over the bacterium and directs its growth and reproductive activities to express the phage genes and to produce progeny phages.

One of two pathways in the life cycle of temperate phages in which the phage genome is integrated into the host cell’s chromosome and progeny phages are not formed.

Referring to a bacterium that contains the genome of a temperate phage in the prophage state. On induction, the prophage leaves the bacterial chromosome, progeny phages are produced, and the bacterial cell lyses.

The phenomenon in which the genome of a temperate phage is inserted into a bacterial chromosome, where it replicates when the bacterial chromosome replicates. In this state, the phage genes are repressed and progeny phages are not formed.

Loops of supercoiled DNA that serve to compact the chromosomes.

Sequence variations among individuals in a specific region of DNA that are detected by molecular analysis of the DNA and can be used in genetic analysis. See also gene markers.

dicentric chromosome [image]

A homologous chromosome pair in meiosis I in which one chromatid has two centromeres as the result of crossing-over within a paracentric inversion. As the two centromeres begin to migrate to opposite poles, a dicentric bridge stretching across the cell forms and eventually breaks.

A technique for detecting chromosomes carrying a particular DNA sequence by hybridizing them with a cloned DNA probe that is tagged with a fluorescent chemical. The chromosomes are treated to separate the double-stranded DNA into single strands, which base-pair with a probe whose sequence is complementary to a region of the chromosomal DNA.

In E. coli, an episome that confers the ability to act as a donor cell in conjugation. Excision of an F factor from the bacterial chromosome may generate an F? factor, which carries a few host cell genes. See also F-duction.

Hairlike cell surface components produced by cells containing the F factor, which allow the physical union of F+ and F? cells or Hfr and F? cells to take place. Also called sex pili.

Transfer of host genes carried on an F? factor in conjugation between an F? and an F? cell. If the genes are different between the two cell types, the recipient becomes partially diploid for the genes on the F?.

Chromatin that may become condensed and therefore transcriptionally inactive in certain cell types, at different developmental stages, or in one member of a homologous chromosome pair.

A rodent cell line that carries a small fragment of the genome of another organism, such as a human.

A type of nonreciprocal translocation in which the long arms of two nonhomologous acrocentric chromosomes become attached to a single centromere.

A gene whose protein product promotes cell proliferation. Oncogenes are altered forms of proto-oncogenes.

Short DNA molecule; also called oligonucleotide.

The hypothesis that each gene controls the synthesis of one enzyme.

The hypothesis that each gene controls the synthesis of a polypeptide chain.

For a microorganism, a medium that supplies all the ingredients required for growth and reproduction, including those normally produced by the wild-type organism.

The simultaneous transduction of two or more bacterial genes, a good indication that the bacterial genes are closely linked.

A test used to determine whether two independently isolated mutations that confer the same phenotype are located within the same gene or in two different genes. Also called cis-trans test.

The amount of DNA found in the haploid set of chromosomes.

Condensed chromatin that is always transcriptionally inactive and is found at homologous sites on chromosome pairs.

Nucleotide sequence of DNA in the centromere region of chromosomes. CEN sequences differ among species and between chromosomes in the same species.

A procedure in which a sample of chorionic villus tissue of a developing fetus is examined for chromosomal abnormalities.

In bacteria, a plasmid that is capable of integrating into the host cell’s chromosome.

Chromatin that is condensed during mitosis but becomes uncoiled during interphase, when it can be transcribed. See also heterochromatin.

Viruses that attack bacteria. Also called phages.

A bacteriophage, such as T4, that always follows the lytic cycle when it infects bacteria. See also temperate phage.

A type of transduction in which any gene may be transferred from one bacterium to another.

A nonreciprocal recombination process in which one allele in a heterozygote is changed to the other allele, thus converting a heterozygous genotype to a homozygous genotype.

A biochemical disorder caused by mutation in a gene encoding an enzyme in a particular metabolic pathway.

A type of transduction in which only specific genes are transferred from one bacterium to another.

Referring to a double-stranded DNA molecule that is twisted in space about its own axis.