Sex Chromosomes: The homologous chromosomes that are dissimilar in the heterogametic sex. There are the X CHROMOSOME, the Y CHROMOSOME, and the W, Z chromosomes (in animals in which the female is the heterogametic sex (the silkworm moth Bombyx mori, for example)). In such cases the W chromosome is the female-determining and the male is ZZ. (From King & Stansfield, A Dictionary of Genetics, 4th ed)Chromosomes: In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Sex Chromosome Aberrations: Abnormal number or structure of the SEX CHROMOSOMES. Some sex chromosome aberrations are associated with SEX CHROMOSOME DISORDERS and SEX CHROMOSOME DISORDERS OF SEX DEVELOPMENT.Chromosome Mapping: Any method used for determining the location of and relative distances between genes on a chromosome.X Chromosome: The female sex chromosome, being the differential sex chromosome carried by half the male gametes and all female gametes in human and other male-heterogametic species.Y Chromosome: The male sex chromosome, being the differential sex chromosome carried by half the male gametes and none of the female gametes in humans and in some other male-heterogametic species in which the homologue of the X chromosome has been retained.Sex Chromosome Disorders: Clinical conditions caused by an abnormal sex chromosome constitution (SEX CHROMOSOME ABERRATIONS), in which there is extra or missing sex chromosome material (either a whole chromosome or a chromosome segment).Chromosome Banding: Staining of bands, or chromosome segments, allowing the precise identification of individual chromosomes or parts of chromosomes. Applications include the determination of chromosome rearrangements in malformation syndromes and cancer, the chemistry of chromosome segments, chromosome changes during evolution, and, in conjunction with cell hybridization studies, chromosome mapping.Chromosomes, Human, X: The human female sex chromosome, being the differential sex chromosome carried by half the male gametes and all female gametes in humans.Chromosome Aberrations: Abnormal number or structure of chromosomes. Chromosome aberrations may result in CHROMOSOME DISORDERS.Chromosomes, Human, Y: The human male sex chromosome, being the differential sex chromosome carried by half the male gametes and none of the female gametes in humans.Sex Determination Processes: The mechanisms by which the SEX of an individual's GONADS are fixed.Chromosome Pairing: The alignment of CHROMOSOMES at homologous sequences.Chromosomes, Plant: Complex nucleoprotein structures which contain the genomic DNA and are part of the CELL NUCLEUS of PLANTS.Silene: A plant genus of the family CARYOPHYLLACEAE. The common name of campion is also used with LYCHNIS. The common name of 'pink' can be confused with other plants.X Chromosome Inactivation: A dosage compensation process occurring at an early embryonic stage in mammalian development whereby, at random, one X CHROMOSOME of the pair is repressed in the somatic cells of females.Chromosome Segregation: The orderly segregation of CHROMOSOMES during MEIOSIS or MITOSIS.In Situ Hybridization, Fluorescence: A type of IN SITU HYBRIDIZATION in which target sequences are stained with fluorescent dye so their location and size can be determined using fluorescence microscopy. This staining is sufficiently distinct that the hybridization signal can be seen both in metaphase spreads and in interphase nuclei.Chromosomes, Human: Very long DNA molecules and associated proteins, HISTONES, and non-histone chromosomal proteins (CHROMOSOMAL PROTEINS, NON-HISTONE). Normally 46 chromosomes, including two sex chromosomes are found in the nucleus of human cells. They carry the hereditary information of the individual.Karyotyping: Mapping of the KARYOTYPE of a cell.Chromosomes, Human, Pair 1: A specific pair of human chromosomes in group A (CHROMOSOMES, HUMAN, 1-3) of the human chromosome classification.Genes, Y-Linked: Genes that are located on the Y CHROMOSOME.Genes, X-Linked: Genes that are located on the X CHROMOSOME.Aneuploidy: The chromosomal constitution of cells which deviate from the normal by the addition or subtraction of CHROMOSOMES, chromosome pairs, or chromosome fragments. In a normally diploid cell (DIPLOIDY) the loss of a chromosome pair is termed nullisomy (symbol: 2N-2), the loss of a single chromosome is MONOSOMY (symbol: 2N-1), the addition of a chromosome pair is tetrasomy (symbol: 2N+2), the addition of a single chromosome is TRISOMY (symbol: 2N+1).Chromosome Painting: A technique for visualizing CHROMOSOME ABERRATIONS using fluorescently labeled DNA probes which are hybridized to chromosomal DNA. Multiple fluorochromes may be attached to the probes. Upon hybridization, this produces a multicolored, or painted, effect with a unique color at each site of hybridization. This technique may also be used to identify cross-species homology by labeling probes from one species for hybridization with chromosomes from another species.Chromosomes, Artificial, Bacterial: DNA constructs that are composed of, at least, a REPLICATION ORIGIN, for successful replication, propagation to and maintenance as an extra chromosome in bacteria. In addition, they can carry large amounts (about 200 kilobases) of other sequence for a variety of bioengineering purposes.Chromosomes, Bacterial: Structures within the nucleus of bacterial cells consisting of or containing DNA, which carry genetic information essential to the cell.Chromosomes, Human, Pair 21: A specific pair of GROUP G CHROMOSOMES of the human chromosome classification.Platypus: A small aquatic oviparous mammal of the order Monotremata found in Australia and Tasmania.Chromosomes, Insect: Structures within the CELL NUCLEUS of insect cells containing DNA.Sex Characteristics: Those characteristics that distinguish one SEX from the other. The primary sex characteristics are the OVARIES and TESTES and their related hormones. Secondary sex characteristics are those which are masculine or feminine but not directly related to reproduction.Meiosis: A type of CELL NUCLEUS division, occurring during maturation of the GERM CELLS. Two successive cell nucleus divisions following a single chromosome duplication (S PHASE) result in daughter cells with half the number of CHROMOSOMES as the parent cells.Chromosomes, Human, Pair 7: A specific pair of GROUP C CHROMOSOMES of the human chromosome classification.Chromosomes, Human, Pair 11: A specific pair of GROUP C CHROMOSOMES of the human chromosome classification.Chromosomes, Human, Pair 17: A specific pair of GROUP E CHROMOSOMES of the human chromosome classification.Sex Chromatin: In the interphase nucleus, a condensed mass of chromatin representing an inactivated X chromosome. Each X CHROMOSOME, in excess of one, forms sex chromatin (Barr body) in the mammalian nucleus. (from King & Stansfield, A Dictionary of Genetics, 4th ed)Chromosome Deletion: Actual loss of portion of a chromosome.Klinefelter Syndrome: A form of male HYPOGONADISM, characterized by the presence of an extra X CHROMOSOME, small TESTES, seminiferous tubule dysgenesis, elevated levels of GONADOTROPINS, low serum TESTOSTERONE, underdeveloped secondary sex characteristics, and male infertility (INFERTILITY, MALE). Patients tend to have long legs and a slim, tall stature. GYNECOMASTIA is present in many of the patients. The classic form has the karyotype 47,XXY. Several karyotype variants include 48,XXYY; 48,XXXY; 49,XXXXY, and mosaic patterns ( 46,XY/47,XXY; 47,XXY/48,XXXY, etc.).Chromosomes, Fungal: Structures within the nucleus of fungal cells consisting of or containing DNA, which carry genetic information essential to the cell.Chromosomes, Human, Pair 6: A specific pair GROUP C CHROMSOMES of the human chromosome classification.Chromosome Disorders: Clinical conditions caused by an abnormal chromosome constitution in which there is extra or missing chromosome material (either a whole chromosome or a chromosome segment). (from Thompson et al., Genetics in Medicine, 5th ed, p429)XYY Karyotype: Abnormal genetic constitution in males characterized by an extra Y chromosome.Chromosomes, Mammalian: Complex nucleoprotein structures which contain the genomic DNA and are part of the CELL NUCLEUS of MAMMALS.Chromosomes, Human, Pair 9: A specific pair of GROUP C CHROMSOMES of the human chromosome classification.Chromosomes, Human, Pair 13: A specific pair of GROUP D CHROMOSOMES of the human chromosome classification.Chromosomes, Human, Pair 18: A specific pair of GROUP E CHROMOSOMES of the human chromosome classification.Spermatocytes: Male germ cells derived from SPERMATOGONIA. The euploid primary spermatocytes undergo MEIOSIS and give rise to the haploid secondary spermatocytes which in turn give rise to SPERMATIDS.Genes, sry: The primary testis-determining gene in mammalians, located on the Y CHROMOSOME. It codes for a high mobility group box transcription factor (TRANSCRIPTION FACTORS) which initiates the development of the TESTES from the embryonic GONADS.Pachytene Stage: The stage in the first meiotic prophase, following ZYGOTENE STAGE, when CROSSING OVER between homologous CHROMOSOMES begins.Chromosome Structures: Structures which are contained in or part of CHROMOSOMES.Chromosomes, Human, 6-12 and X: The medium-sized, submetacentric human chromosomes, called group C in the human chromosome classification. This group consists of chromosome pairs 6, 7, 8, 9, 10, 11, and 12 and the X chromosome.Genetic Linkage: The co-inheritance of two or more non-allelic GENES due to their being located more or less closely on the same CHROMOSOME.Evolution, Molecular: The process of cumulative change at the level of DNA; RNA; and PROTEINS, over successive generations.Dosage Compensation, Genetic: Genetic mechanisms that allow GENES to be expressed at a similar level irrespective of their GENE DOSAGE. This term is usually used in discussing genes that lie on the SEX CHROMOSOMES. Because the sex chromosomes are only partially homologous, there is a different copy number, i.e., dosage, of these genes in males vs. females. In DROSOPHILA, dosage compensation is accomplished by hypertranscription of genes located on the X CHROMOSOME. In mammals, dosage compensation of X chromosome genes is accomplished by random X CHROMOSOME INACTIVATION of one of the two X chromosomes in the female.Chromosomes, Human, Pair 2: A specific pair of human chromosomes in group A (CHROMOSOMES, HUMAN, 1-3) of the human chromosome classification.Chromosomes, Human, Pair 16: A specific pair of GROUP E CHROMOSOMES of the human chromosome classification.Chromosomes, Human, Pair 22: A specific pair of GROUP G CHROMOSOMES of the human chromosome classification.Carica: A plant genus of the family Caricaceae, order Violales, subclass Dilleniidae, class Magnoliopsida. It is the source of edible fruit and PAPAIN.Chromosomes, Human, Pair 4: A specific pair of GROUP B CHROMOSOMES of the human chromosome classification.Chromosomes, Human, Pair 10: A specific pair of GROUP C CHROMOSOMES of the human chromosome classification.Chromosomes, Human, Pair 8: A specific pair of GROUP C CHROMOSOMES of the human chromosome classification.Chromosomes, Human, Pair 19: A specific pair of GROUP F CHROMOSOMES of the human chromosome classification.Sex Factors: Maleness or femaleness as a constituent element or influence contributing to the production of a result. It may be applicable to the cause or effect of a circumstance. It is used with human or animal concepts but should be differentiated from SEX CHARACTERISTICS, anatomical or physiological manifestations of sex, and from SEX DISTRIBUTION, the number of males and females in given circumstances.Chromosomes, Human, Pair 20: A specific pair of GROUP F CHROMOSOMES of the human chromosome classification.Sex Differentiation: The process in developing sex- or gender-specific tissue, organ, or function after SEX DETERMINATION PROCESSES have set the sex of the GONADS. Major areas of sex differentiation occur in the reproductive tract (GENITALIA) and the brain.Chromosomes, Human, Pair 12: A specific pair of GROUP C CHROMOSOMES of the human chromosome classification.Chromosomes, Human, 1-3: The large, metacentric human chromosomes, called group A in the human chromosome classification. This group consists of chromosome pairs 1, 2, and 3.Chromosomes, Human, Pair 5: One of the two pairs of human chromosomes in the group B class (CHROMOSOMES, HUMAN, 4-5).Genetic Markers: A phenotypically recognizable genetic trait which can be used to identify a genetic locus, a linkage group, or a recombination event.Chromosomes, Human, Pair 15: A specific pair of GROUP D CHROMOSOMES of the human chromosome classification.Mosaicism: The occurrence in an individual of two or more cell populations of different chromosomal constitutions, derived from a single ZYGOTE, as opposed to CHIMERISM in which the different cell populations are derived from more than one zygote.Chromosomes, Human, 21-22 and Y: The short, acrocentric human chromosomes, called group G in the human chromosome classification. This group consists of chromosome pairs 21 and 22 and the Y chromosome.Recombination, Genetic: Production of new arrangements of DNA by various mechanisms such as assortment and segregation, CROSSING OVER; GENE CONVERSION; GENETIC TRANSFORMATION; GENETIC CONJUGATION; GENETIC TRANSDUCTION; or mixed infection of viruses.Chromosome Inversion: An aberration in which a chromosomal segment is deleted and reinserted in the same place but turned 180 degrees from its original orientation, so that the gene sequence for the segment is reversed with respect to that of the rest of the chromosome.Chromosomes, Human, Pair 14: A specific pair of GROUP D CHROMOSOMES of the human chromosome classification.Chromosomes, Human, 16-18: The short, submetacentric human chromosomes, called group E in the human chromosome classification. This group consists of chromosome pairs 16, 17, and 18.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Chromosomes, Artificial, Yeast: Chromosomes in which fragments of exogenous DNA ranging in length up to several hundred kilobase pairs have been cloned into yeast through ligation to vector sequences. These artificial chromosomes are used extensively in molecular biology for the construction of comprehensive genomic libraries of higher organisms.Chromosomes, Human, 13-15: The medium-sized, acrocentric human chromosomes, called group D in the human chromosome classification. This group consists of chromosome pairs 13, 14, and 15.Crosses, Genetic: Deliberate breeding of two different individuals that results in offspring that carry part of the genetic material of each parent. The parent organisms must be genetically compatible and may be from different varieties or closely related species.Sex Determination Analysis: Validation of the SEX of an individual by inspection of the GONADS and/or by genetic tests.Centromere: The clear constricted portion of the chromosome at which the chromatids are joined and by which the chromosome is attached to the spindle during cell division.Turner Syndrome: A syndrome of defective gonadal development in phenotypic females associated with the karyotype 45,X (or 45,XO). Patients generally are of short stature with undifferentiated GONADS (streak gonads), SEXUAL INFANTILISM, HYPOGONADISM, webbing of the neck, cubitus valgus, elevated GONADOTROPINS, decreased ESTRADIOL level in blood, and CONGENITAL HEART DEFECTS. NOONAN SYNDROME (also called Pseudo-Turner Syndrome and Male Turner Syndrome) resembles this disorder; however, it occurs in males and females with a normal karyotype and is inherited as an autosomal dominant.Chromosome Breakage: A type of chromosomal aberration involving DNA BREAKS. Chromosome breakage can result in CHROMOSOMAL TRANSLOCATION; CHROMOSOME INVERSION; or SEQUENCE DELETION.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Translocation, Genetic: A type of chromosome aberration characterized by CHROMOSOME BREAKAGE and transfer of the broken-off portion to another location, often to a different chromosome.Karyotype: The full set of CHROMOSOMES presented as a systematized array of METAPHASE chromosomes from a photomicrograph of a single CELL NUCLEUS arranged in pairs in descending order of size and according to the position of the CENTROMERE. (From Stedman, 25th ed)Ring Chromosomes: Aberrant chromosomes with no ends, i.e., circular.Disorders of Sex Development: In gonochoristic organisms, congenital conditions in which development of chromosomal, gonadal, or anatomical sex is atypical. Effects from exposure to abnormal levels of GONADAL HORMONES in the maternal environment, or disruption of the function of those hormones by ENDOCRINE DISRUPTORS are included.Models, Genetic: Theoretical representations that simulate the behavior or activity of genetic processes or phenomena. They include the use of mathematical equations, computers, and other electronic equipment.Spermatogenesis: The process of germ cell development in the male from the primordial germ cells, through SPERMATOGONIA; SPERMATOCYTES; SPERMATIDS; to the mature haploid SPERMATOZOA.Biological Evolution: The process of cumulative change over successive generations through which organisms acquire their distinguishing morphological and physiological characteristics.Trisomy: The possession of a third chromosome of any one type in an otherwise diploid cell.Chromosome Positioning: The mechanisms of eukaryotic CELLS that place or keep the CHROMOSOMES in a particular SUBNUCLEAR SPACE.Nondisjunction, Genetic: The failure of homologous CHROMOSOMES or CHROMATIDS to segregate during MITOSIS or MEIOSIS with the result that one daughter cell has both of a pair of parental chromosomes or chromatids and the other has none.Chromosomes, Human, 4-5: The large, submetacentric human chromosomes, called group B in the human chromosome classification. This group consists of chromosome pairs 4 and 5.Sex Chromosome Disorders of Sex Development: Congenital conditions of atypical sexual development associated with abnormal sex chromosome constitutions including MONOSOMY; TRISOMY; and MOSAICISM.Metaphase: The phase of cell nucleus division following PROMETAPHASE, in which the CHROMOSOMES line up across the equatorial plane of the SPINDLE APPARATUS prior to separation.Spermatozoa: Mature male germ cells derived from SPERMATIDS. As spermatids move toward the lumen of the SEMINIFEROUS TUBULES, they undergo extensive structural changes including the loss of cytoplasm, condensation of CHROMATIN into the SPERM HEAD, formation of the ACROSOME cap, the SPERM MIDPIECE and the SPERM TAIL that provides motility.Microsatellite Repeats: A variety of simple repeat sequences that are distributed throughout the GENOME. They are characterized by a short repeat unit of 2-8 basepairs that is repeated up to 100 times. They are also known as short tandem repeats (STRs).Dromaiidae: A family of flightless, running BIRDS, in the order Casuariiformes. The emu is the only surviving member of the family. They naturally inhabit forests, open plains, and grasslands in Australia.Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Marsupialia: An infraclass of MAMMALS, also called Metatheria, where the young are born at an early stage of development and continue to develop in a pouch (marsupium). In contrast to Eutheria (placentals), marsupials have an incomplete PLACENTA.Sex: The totality of characteristics of reproductive structure, functions, PHENOTYPE, and GENOTYPE, differentiating the MALE from the FEMALE organism.Diploidy: The chromosomal constitution of cells, in which each type of CHROMOSOME is represented twice. Symbol: 2N or 2X.Infertility, Male: The inability of the male to effect FERTILIZATION of an OVUM after a specified period of unprotected intercourse. Male sterility is permanent infertility.Mitosis: A type of CELL NUCLEUS division by means of which the two daughter nuclei normally receive identical complements of the number of CHROMOSOMES of the somatic cells of the species.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.Sequence Analysis, DNA: A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA SEQUENCE, and information analysis.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Chromosome Duplication: An aberration in which an extra chromosome or a chromosomal segment is made.Alleles: Variant forms of the same gene, occupying the same locus on homologous CHROMOSOMES, and governing the variants in production of the same gene product.Hybrid Cells: Any cell, other than a ZYGOTE, that contains elements (such as NUCLEI and CYTOPLASM) from two or more different cells, usually produced by artificial CELL FUSION.Smegmamorpha: Group of fish under the superorder Acanthopterygii, separate from the PERCIFORMES, which includes swamp eels, mullets, sticklebacks, seahorses, spiny eels, rainbowfishes, and KILLIFISHES. The name is derived from the six taxa which comprise the group. (From http://www.nanfa.org/articles/Elassoma/elassoma.htm, 8/4/2000)Chromosomes, Human, 19-20: The short, metacentric human chromosomes, called group F in the human chromosome classification. This group consists of chromosome pairs 19 and 20.Chromosomes, Artificial: DNA constructs that are composed of, at least, elements such as a REPLICATION ORIGIN; TELOMERE; and CENTROMERE, that are required for successful replication, propagation to and maintenance in progeny cells. In addition, they are constructed to carry other sequences for analysis or gene transfer.Prophase: The first phase of cell nucleus division, in which the CHROMOSOMES become visible, the CELL NUCLEUS starts to lose its identity, the SPINDLE APPARATUS appears, and the CENTRIOLES migrate toward opposite poles.Gene Dosage: The number of copies of a given gene present in the cell of an organism. An increase in gene dosage (by GENE DUPLICATION for example) can result in higher levels of gene product formation. GENE DOSAGE COMPENSATION mechanisms result in adjustments to the level GENE EXPRESSION when there are changes or differences in gene dosage.Sex Ratio: The number of males per 100 females.Testis: The male gonad containing two functional parts: the SEMINIFEROUS TUBULES for the production and transport of male germ cells (SPERMATOGENESIS) and the interstitial compartment containing LEYDIG CELLS that produce ANDROGENS.Pedigree: The record of descent or ancestry, particularly of a particular condition or trait, indicating individual family members, their relationships, and their status with respect to the trait or condition.Cytogenetic Analysis: Examination of CHROMOSOMES to diagnose, classify, screen for, or manage genetic diseases and abnormalities. Following preparation of the sample, KARYOTYPING is performed and/or the specific chromosomes are analyzed.Muntjacs: A genus, Muntiacus, of the deer family (Cervidae) comprising six species living in China, Tibet, Nepal, India, the Malay Peninsula, and neighboring island countries. They are usually found in forests and areas of dense vegetation, usually not far from water. They emit a deep barklike sound which gives them the name "barking deer." If they sense a predator they will "bark" for an hour or more. They are hunted for their meat and skins; they thrive in captivity and are found in many zoos. The Indian muntjac is believed to have the lowest chromosome number in mammals and cell lines derived from them figure widely in chromosome and DNA studies. (From Walker's Mammals of the World, 5th ed., p1366)Spermatids: Male germ cells derived from the haploid secondary SPERMATOCYTES. Without further division, spermatids undergo structural changes and give rise to SPERMATOZOA.Characiformes: An order of fresh water fish with 18 families and over 1600 species. The order includes CHARACINS, hatchetfish, piranhas, and TETRAS.Gonadal Dysgenesis, Mixed: A type of defective gonadal development in patients with a wide spectrum of chromosomal mosaic variants. Their karyotypes are of partial sex chromosome monosomy resulting from an absence or an abnormal second sex chromosome (X or Y). Karyotypes include 45,X/46,XX; 45,X/46,XX/47,XXX; 46,XXp-; 45,X/46,XY; 45,X/47,XYY; 46,XYpi; etc. The spectrum of phenotypes may range from phenotypic female to phenotypic male including variations in gonads and internal and external genitalia, depending on the ratio in each gonad of 45,X primordial germ cells to those with normal 46,XX or 46,XY constitution.Genotype: The genetic constitution of the individual, comprising the ALLELES present at each GENETIC LOCUS.Meiotic Prophase I: The prophase of the first division of MEIOSIS (in which homologous CHROMOSOME SEGREGATION occurs). It is divided into five stages: leptonema, zygonema, PACHYNEMA, diplonema, and diakinesis.Drosophila melanogaster: A species of fruit fly much used in genetics because of the large size of its chromosomes.DNA, Satellite: Highly repetitive DNA sequences found in HETEROCHROMATIN, mainly near centromeres. They are composed of simple sequences (very short) (see MINISATELLITE REPEATS) repeated in tandem many times to form large blocks of sequence. Additionally, following the accumulation of mutations, these blocks of repeats have been repeated in tandem themselves. The degree of repetition is on the order of 1000 to 10 million at each locus. Loci are few, usually one or two per chromosome. They were called satellites since in density gradients, they often sediment as distinct, satellite bands separate from the bulk of genomic DNA owing to a distinct BASE COMPOSITION.Lod Score: The total relative probability, expressed on a logarithmic scale, that a linkage relationship exists among selected loci. Lod is an acronym for "logarithmic odds."Sex-Determining Region Y Protein: A transcription factor that plays an essential role in the development of the TESTES. It is encoded by a gene on the Y chromosome and contains a specific HMG-BOX DOMAIN that is found within members of the SOX family of transcription factors.Monosomy: The condition in which one chromosome of a pair is missing. In a normally diploid cell it is represented symbolically as 2N-1.Genetic Variation: Genotypic differences observed among individuals in a population.Diptera: An order of the class Insecta. Wings, when present, number two and distinguish Diptera from other so-called flies, while the halteres, or reduced hindwings, separate Diptera from other insects with one pair of wings. The order includes the families Calliphoridae, Oestridae, Phoridae, SARCOPHAGIDAE, Scatophagidae, Sciaridae, SIMULIIDAE, Tabanidae, Therevidae, Trypetidae, CERATOPOGONIDAE; CHIRONOMIDAE; CULICIDAE; DROSOPHILIDAE; GLOSSINIDAE; MUSCIDAE; TEPHRITIDAE; and PSYCHODIDAE. The larval form of Diptera species are called maggots (see LARVA).DNA Probes: Species- or subspecies-specific DNA (including COMPLEMENTARY DNA; conserved genes, whole chromosomes, or whole genomes) used in hybridization studies in order to identify microorganisms, to measure DNA-DNA homologies, to group subspecies, etc. The DNA probe hybridizes with a specific mRNA, if present. Conventional techniques used for testing for the hybridization product include dot blot assays, Southern blot assays, and DNA:RNA hybrid-specific antibody tests. Conventional labels for the DNA probe include the radioisotope labels 32P and 125I and the chemical label biotin. The use of DNA probes provides a specific, sensitive, rapid, and inexpensive replacement for cell culture techniques for diagnosing infections.Repetitive Sequences, Nucleic Acid: Sequences of DNA or RNA that occur in multiple copies. There are several types: INTERSPERSED REPETITIVE SEQUENCES are copies of transposable elements (DNA TRANSPOSABLE ELEMENTS or RETROELEMENTS) dispersed throughout the genome. TERMINAL REPEAT SEQUENCES flank both ends of another sequence, for example, the long terminal repeats (LTRs) on RETROVIRUSES. Variations may be direct repeats, those occurring in the same direction, or inverted repeats, those opposite to each other in direction. TANDEM REPEAT SEQUENCES are copies which lie adjacent to each other, direct or inverted (INVERTED REPEAT SEQUENCES).DNA: A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine).Cloning, Molecular: The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells.Oligospermia: A condition of suboptimal concentration of SPERMATOZOA in the ejaculated SEMEN to ensure successful FERTILIZATION of an OVUM. In humans, oligospermia is defined as a sperm count below 20 million per milliliter semen.Cytogenetics: A subdiscipline of genetics which deals with the cytological and molecular analysis of the CHROMOSOMES, and location of the GENES on chromosomes, and the movements of chromosomes during the CELL CYCLE.Telomere: A terminal section of a chromosome which has a specialized structure and which is involved in chromosomal replication and stability. Its length is believed to be a few hundred base pairs.Nucleic Acid Hybridization: Widely used technique which exploits the ability of complementary sequences in single-stranded DNAs or RNAs to pair with each other to form a double helix. Hybridization can take place between two complimentary DNA sequences, between a single-stranded DNA and a complementary RNA, or between two RNA sequences. The technique is used to detect and isolate specific sequences, measure homology, or define other characteristics of one or both strands. (Kendrew, Encyclopedia of Molecular Biology, 1994, p503)Drosophila: A genus of small, two-winged flies containing approximately 900 described species. These organisms are the most extensively studied of all genera from the standpoint of genetics and cytology.Sex Preselection: Methods for controlling genetic SEX of offspring.Physical Chromosome Mapping: Mapping of the linear order of genes on a chromosome with units indicating their distances by using methods other than genetic recombination. These methods include nucleotide sequencing, overlapping deletions in polytene chromosomes, and electron micrography of heteroduplex DNA. (From King & Stansfield, A Dictionary of Genetics, 5th ed)Genes, Insect: The functional hereditary units of INSECTS.Species Specificity: The restriction of a characteristic behavior, anatomical structure or physical system, such as immune response; metabolic response, or gene or gene variant to the members of one species. It refers to that property which differentiates one species from another but it is also used for phylogenetic levels higher or lower than the species.Chromosomal Proteins, Non-Histone: Nucleoproteins, which in contrast to HISTONES, are acid insoluble. They are involved in chromosomal functions; e.g. they bind selectively to DNA, stimulate transcription resulting in tissue-specific RNA synthesis and undergo specific changes in response to various hormones or phytomitogens.Chromatin: The material of CHROMOSOMES. It is a complex of DNA; HISTONES; and nonhistone proteins (CHROMOSOMAL PROTEINS, NON-HISTONE) found within the nucleus of a cell.Synaptonemal Complex: The three-part structure of ribbon-like proteinaceous material that serves to align and join the paired homologous CHROMOSOMES. It is formed during the ZYGOTENE STAGE of the first meiotic division. It is a prerequisite for CROSSING OVER.Genome: The genetic complement of an organism, including all of its GENES, as represented in its DNA, or in some cases, its RNA.Polymerase Chain Reaction: In vitro method for producing large amounts of specific DNA or RNA fragments of defined length and sequence from small amounts of short oligonucleotide flanking sequences (primers). The essential steps include thermal denaturation of the double-stranded target molecules, annealing of the primers to their complementary sequences, and extension of the annealed primers by enzymatic synthesis with DNA polymerase. The reaction is efficient, specific, and extremely sensitive. Uses for the reaction include disease diagnosis, detection of difficult-to-isolate pathogens, mutation analysis, genetic testing, DNA sequencing, and analyzing evolutionary relationships.Echidna: An oviparous burrowing mammal of the order Monotremata native to Australia, Tasmania, and New Guinea. It has hair mingled with spines on the upper part of the body and is adapted for feeding on ants.Haploidy: The chromosomal constitution of cells, in which each type of CHROMOSOME is represented once. Symbol: N.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Birds: Warm-blooded VERTEBRATES possessing FEATHERS and belonging to the class Aves.Heterozygote: An individual having different alleles at one or more loci regarding a specific character.Haplotypes: The genetic constitution of individuals with respect to one member of a pair of allelic genes, or sets of genes that are closely linked and tend to be inherited together such as those of the MAJOR HISTOCOMPATIBILITY COMPLEX.Mammals: Warm-blooded vertebrate animals belonging to the class Mammalia, including all that possess hair and suckle their young.Blotting, Southern: A method (first developed by E.M. Southern) for detection of DNA that has been electrophoretically separated and immobilized by blotting on nitrocellulose or other type of paper or nylon membrane followed by hybridization with labeled NUCLEIC ACID PROBES.Quantitative Trait Loci: Genetic loci associated with a QUANTITATIVE TRAIT.Fragaria: A plant genus of the family ROSACEAE known for the edible fruit.Didelphis: A genus of large OPOSSUMS in the family Didelphidae, found in the Americas. The species Didelphis virginiana is prominent in North America.Polyploidy: The chromosomal constitution of a cell containing multiples of the normal number of CHROMOSOMES; includes triploidy (symbol: 3N), tetraploidy (symbol: 4N), etc.Hybridization, Genetic: The genetic process of crossbreeding between genetically dissimilar parents to produce a hybrid.Polymorphism, Genetic: The regular and simultaneous occurrence in a single interbreeding population of two or more discontinuous genotypes. The concept includes differences in genotypes ranging in size from a single nucleotide site (POLYMORPHISM, SINGLE NUCLEOTIDE) to large nucleotide sequences visible at a chromosomal level.Genes: A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms.Nuclear Proteins: Proteins found in the nucleus of a cell. Do not confuse with NUCLEOPROTEINS which are proteins conjugated with nucleic acids, that are not necessarily present in the nucleus.Chromosomes, Artificial, Human: DNA constructs that are composed of, at least, all elements, such as a REPLICATION ORIGIN; TELOMERE; and CENTROMERE, required for successful replication, propagation to and maintainance in progeny human cells. In addition, they are constructed to carry other sequences for analysis or gene transfer.Kinetochores: Large multiprotein complexes that bind the centromeres of the chromosomes to the microtubules of the mitotic spindle during metaphase in the cell cycle.LizardsGenetic Loci: Specific regions that are mapped within a GENOME. Genetic loci are usually identified with a shorthand notation that indicates the chromosome number and the position of a specific band along the P or Q arm of the chromosome where they are found. For example the locus 6p21 is found within band 21 of the P-arm of CHROMOSOME 6. Many well known genetic loci are also known by common names that are associated with a genetic function or HEREDITARY DISEASE.Histones: Small chromosomal proteins (approx 12-20 kD) possessing an open, unfolded structure and attached to the DNA in cell nuclei by ionic linkages. Classification into the various types (designated histone I, histone II, etc.) is based on the relative amounts of arginine and lysine in each.Heterochromatin: The portion of chromosome material that remains condensed and is transcriptionally inactive during INTERPHASE.Sequence Homology, Nucleic Acid: The sequential correspondence of nucleotides in one nucleic acid molecule with those of another nucleic acid molecule. Sequence homology is an indication of the genetic relatedness of different organisms and gene function.Chromosome Walking: A technique with which an unknown region of a chromosome can be explored. It is generally used to isolate a locus of interest for which no probe is available but that is known to be linked to a gene which has been identified and cloned. A fragment containing a known gene is selected and used as a probe to identify other overlapping fragments which contain the same gene. The nucleotide sequences of these fragments can then be characterized. This process continues for the length of the chromosome.Multigene Family: A set of genes descended by duplication and variation from some ancestral gene. Such genes may be clustered together on the same chromosome or dispersed on different chromosomes. Examples of multigene families include those that encode the hemoglobins, immunoglobulins, histocompatibility antigens, actins, tubulins, keratins, collagens, heat shock proteins, salivary glue proteins, chorion proteins, cuticle proteins, yolk proteins, and phaseolins, as well as histones, ribosomal RNA, and transfer RNA genes. The latter three are examples of reiterated genes, where hundreds of identical genes are present in a tandem array. (King & Stanfield, A Dictionary of Genetics, 4th ed)Retroelements: Elements that are transcribed into RNA, reverse-transcribed into DNA and then inserted into a new site in the genome. Long terminal repeats (LTRs) similar to those from retroviruses are contained in retrotransposons and retrovirus-like elements. Retroposons, such as LONG INTERSPERSED NUCLEOTIDE ELEMENTS and SHORT INTERSPERSED NUCLEOTIDE ELEMENTS do not contain LTRs.Genes, Plant: The functional hereditary units of PLANTS.Genes, Mating Type, Fungal: Fungal genes that mostly encode TRANSCRIPTION FACTORS. In some FUNGI they also encode PHEROMONES and PHEROMONE RECEPTORS. The transcription factors control expression of specific proteins that give a cell its mating identity. Opposite mating type identities are required for mating.Gene Duplication: Processes occurring in various organisms by which new genes are copied. Gene duplication may result in a MULTIGENE FAMILY; supergenes or PSEUDOGENES.Uniparental Disomy: The presence in a cell of two paired chromosomes from the same parent, with no chromosome of that pair from the other parent. This chromosome composition stems from non-disjunction (NONDISJUNCTION, GENETIC) events during MEIOSIS. The disomy may be composed of both homologous chromosomes from one parent (heterodisomy) or a duplicate of one chromosome (isodisomy).DNA-Binding Proteins: Proteins which bind to DNA. The family includes proteins which bind to both double- and single-stranded DNA and also includes specific DNA binding proteins in serum which can be used as markers for malignant diseases.Chromosomal Instability: An increased tendency to acquire CHROMOSOME ABERRATIONS when various processes involved in chromosome replication, repair, or segregation are dysfunctional.Spindle Apparatus: A microtubule structure that forms during CELL DIVISION. It consists of two SPINDLE POLES, and sets of MICROTUBULES that may include the astral microtubules, the polar microtubules, and the kinetochore microtubules.Snakes: Limbless REPTILES of the suborder Serpentes.Unsafe Sex: Sexual behaviors which are high-risk for contracting SEXUALLY TRANSMITTED DISEASES or for producing PREGNANCY.Rumex: A plant genus of the family POLYGONACEAE that contains patientosides and other naphthalene glycosides.Prenatal Diagnosis: Determination of the nature of a pathological condition or disease in the postimplantation EMBRYO; FETUS; or pregnant female before birth.Germ Cells: The reproductive cells in multicellular organisms at various stages during GAMETOGENESIS.Cell Nucleus: Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (CELL NUCLEOLUS). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the ENDOPLASMIC RETICULUM. A cell may contain more than one nucleus. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Chromosome Fragility: Susceptibility of chromosomes to breakage leading to translocation; CHROMOSOME INVERSION; SEQUENCE DELETION; or other CHROMOSOME BREAKAGE related aberrations.Gonads: The gamete-producing glands, OVARY or TESTIS.Polymorphism, Single Nucleotide: A single nucleotide variation in a genetic sequence that occurs at appreciable frequency in the population.Gene Deletion: A genetic rearrangement through loss of segments of DNA or RNA, bringing sequences which are normally separated into close proximity. This deletion may be detected using cytogenetic techniques and can also be inferred from the phenotype, indicating a deletion at one specific locus.Ploidies: The degree of replication of the chromosome set in the karyotype.Genome, Human: The complete genetic complement contained in the DNA of a set of CHROMOSOMES in a HUMAN. The length of the human genome is about 3 billion base pairs.DNA Transposable Elements: Discrete segments of DNA which can excise and reintegrate to another site in the genome. Most are inactive, i.e., have not been found to exist outside the integrated state. DNA transposable elements include bacterial IS (insertion sequence) elements, Tn elements, the maize controlling elements Ac and Ds, Drosophila P, gypsy, and pogo elements, the human Tigger elements and the Tc and mariner elements which are found throughout the animal kingdom.Struthioniformes: An order of flightless birds comprising the ostriches, which naturally inhabit open, low rainfall areas of Africa.Gene Rearrangement: The ordered rearrangement of gene regions by DNA recombination such as that which occurs normally during development.