Inheritance Patterns: The different ways GENES and their ALLELES interact during the transmission of genetic traits that effect the outcome of GENE EXPRESSION.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.Genes, Dominant: Genes that influence the PHENOTYPE both in the homozygous and the heterozygous state.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.Genes, Recessive: Genes that influence the PHENOTYPE only in the homozygous state.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.Penetrance: The percent frequency with which a dominant or homozygous recessive gene or gene combination manifests itself in the phenotype of the carriers. (From Glossary of Genetics, 5th ed)Consanguinity: The magnitude of INBREEDING in humans.Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Myotonia Congenita: Inherited myotonic disorders with early childhood onset MYOTONIA. Muscular hypertrophy is common and myotonia may impair ambulation and other movements. It is classified as Thomsen (autosomal dominant) or Becker (autosomal recessive) generalized myotonia mainly based on the inheritance pattern. Becker type is also clinically more severe. An autosomal dominant variant with milder symptoms and later onset is known as myotonia levior. Mutations in the voltage-dependent skeletal muscle chloride channel are associated with the disorders.Family Health: The health status of the family as a unit including the impact of the health of one member of the family on the family as a unit and on individual family members; also, the impact of family organization or disorganization on the health status of its members.Chromosome Mapping: Any method used for determining the location of and relative distances between genes on a chromosome.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.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.Retinitis Pigmentosa: Hereditary, progressive degeneration of the neuroepithelium of the retina characterized by night blindness and progressive contraction of the visual field.Heterozygote: An individual having different alleles at one or more loci regarding a specific character.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.Genotype: The genetic constitution of the individual, comprising the ALLELES present at each GENETIC LOCUS.Genetic Predisposition to Disease: A latent susceptibility to disease at the genetic level, which may be activated under certain conditions.Syndrome: A characteristic symptom complex.Genetic Markers: A phenotypically recognizable genetic trait which can be used to identify a genetic locus, a linkage group, or a recombination event.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."DNA Mutational Analysis: Biochemical identification of mutational changes in a nucleotide sequence.DNA, Mitochondrial: Double-stranded DNA of MITOCHONDRIA. In eukaryotes, the mitochondrial GENOME is circular and codes for ribosomal RNAs, transfer RNAs, and about 10 proteins.Abnormalities, MultipleX 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.Age of Onset: The age, developmental stage, or period of life at which a disease or the initial symptoms or manifestations of a disease appear in an individual.Genetic Testing: Detection of a MUTATION; GENOTYPE; KARYOTYPE; or specific ALLELES associated with genetic traits, heritable diseases, or predisposition to a disease, or that may lead to the disease in descendants. It includes prenatal genetic testing.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).Homozygote: An individual in which both alleles at a given locus are identical.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.Genetic Variation: Genotypic differences observed among individuals in a population.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.Mutation, Missense: A mutation in which a codon is mutated to one directing the incorporation of a different amino acid. This substitution may result in an inactive or unstable product. (From A Dictionary of Genetics, King & Stansfield, 5th ed)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.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Heredity: The transmission of traits encoded in GENES from parent to offspring.Extrachromosomal Inheritance: Vertical transmission of hereditary characters by DNA from cytoplasmic organelles such as MITOCHONDRIA; CHLOROPLASTS; and PLASTIDS, or from PLASMIDS or viral episomal DNA.Polymorphism, Single Nucleotide: A single nucleotide variation in a genetic sequence that occurs at appreciable frequency in the population.Point Mutation: A mutation caused by the substitution of one nucleotide for another. This results in the DNA molecule having a change in a single base pair.Sequence Analysis, DNA: A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA SEQUENCE, and information analysis.Multifactorial Inheritance: A phenotypic outcome (physical characteristic or disease predisposition) that is determined by more than one gene. Polygenic refers to those determined by many genes, while oligogenic refers to those determined by a few genes.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.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).Genetic Diseases, Inborn: Diseases that are caused by genetic mutations present during embryo or fetal development, although they may be observed later in life. The mutations may be inherited from a parent's genome or they may be acquired in utero.Hybridization, Genetic: The genetic process of crossbreeding between genetically dissimilar parents to produce a hybrid.Epigenesis, Genetic: A genetic process by which the adult organism is realized via mechanisms that lead to the restriction in the possible fates of cells, eventually leading to their differentiated state. Mechanisms involved cause heritable changes to cells without changes to DNA sequence such as DNA METHYLATION; HISTONE modification; DNA REPLICATION TIMING; NUCLEOSOME positioning; and heterochromatization which result in selective gene expression or repression.Genetics, Medical: A subdiscipline of human genetics which entails the reliable prediction of certain human disorders as a function of the lineage and/or genetic makeup of an individual or of any two parents or potential parents.Genomic Imprinting: The variable phenotypic expression of a GENE depending on whether it is of paternal or maternal origin, which is a function of the DNA METHYLATION pattern. Imprinted regions are observed to be more methylated and less transcriptionally active. (Segen, Dictionary of Modern Medicine, 1992)Genetics: The branch of science concerned with the means and consequences of transmission and generation of the components of biological inheritance. (Stedman, 26th ed)Genes, Mitochondrial: Genes that are located on the MITOCHONDRIAL DNA. Mitochondrial inheritance is often referred to as maternal inheritance but should be differentiated from maternal inheritance that is transmitted chromosomally.Genetic Heterogeneity: The presence of apparently similar characters for which the genetic evidence indicates that different genes or different genetic mechanisms are involved in different pedigrees. In clinical settings genetic heterogeneity refers to the presence of a variety of genetic defects which cause the same disease, often due to mutations at different loci on the same gene, a finding common to many human diseases including ALZHEIMER DISEASE; CYSTIC FIBROSIS; LIPOPROTEIN LIPASE DEFICIENCY, FAMILIAL; and POLYCYSTIC KIDNEY DISEASES. (Rieger, et al., Glossary of Genetics: Classical and Molecular, 5th ed; Segen, Dictionary of Modern Medicine, 1992)Bivalvia: A class in the phylum MOLLUSCA comprised of mussels; clams; OYSTERS; COCKLES; and SCALLOPS. They are characterized by a bilaterally symmetrical hinged shell and a muscular foot used for burrowing and anchoring.Gene Frequency: The proportion of one particular in the total of all ALLELES for one genetic locus in a breeding POPULATION.