A diploid individual's paired alleles can segregate into gametes.
Key knowledge
In ordinary Mendelian segregation, the two alleles at a locus in a diploid individual separate during gamete formation, so each gamete receives one of them. Fertilization combines parental alleles. This discrete inheritance differs from permanent blending of parental hereditary factors.
Conditions and scope
Assumes ordinary segregation of the specified locus; a probability of one half is an expectation, not a guaranteed ratio in a small family.
Dominance and independent assortment have limits: linked genes and non-Mendelian inheritance require additional models.
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References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Published Mendelian segregation model and its stated extensions; no breeding experiment was repeated.
2026-10-10 · English diploid/gamete scope checked against section 12.3 and NHGRI; no claim that all traits follow a simple dominant/recessive pattern.
Foundational review
2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.
Sources from other places
Agreement within this scope
Discrete alleles and ordinary Mendelian segregation into gametes.
Expected ratios are probabilities; small families need not reproduce them exactly.
In typical diploid meiosis, one round of DNA replication is followed by two nuclear divisions that reduce two chromosome sets to one. Homologous chromosomes separate in meiosis I, and sister chromatids separate in meiosis II. Crossing over and independent assortment can reshuffle inherited variants.
In ordinary Mendelian segregation, the two alleles at a locus in a diploid individual separate during gamete formation, so each gamete receives one of them. Fertilization combines parental alleles. This discrete inheritance differs from permanent blending of parental hereditary factors.
Meiotic chromosome segregation provides the cellular context for ordinary Mendelian segregation.
In ordinary Mendelian segregation, the two alleles at a locus in a diploid individual separate during gamete formation, so each gamete receives one of them. Fertilization combines parental alleles. This discrete inheritance differs from permanent blending of parental hereditary factors.
Biological evolution is descent with inherited modification. At the population level, a change in allele frequencies across generations is one way to describe evolutionary change; an individual's growth or temporary acclimation is not, by itself, such a change.
Population genetics connects inherited alleles with changes in their frequencies.
Incomplete dominance produces an intermediate heterozygote phenotype, whereas codominance expresses distinguishable contributions from both alleles. A population can contain more than two alleles at a locus. Such patterns extend simple dominant/recessive models without necessarily changing allele segregation.
Phenotype dominance can differ while Mendelian segregation assumptions still hold.
Linked loci share a chromosome; meiotic recombination can separate their alleles. Recombinant offspring fractions estimate linkage distances for sufficiently close loci. In the standard Mendelian linkage model, the expected recombinant fraction is at most one half; a finite scored offspring sample can exceed that value through sampling fluctuation or distorted class recovery. Multiple crossovers can hide events, so this fraction is not a linear measure of large physical distances.
For an autosomal diploid two-allele locus, random union of gametes with frequencies p and q gives genotype proportions p², 2pq and q². Constancy across generations additionally requires the idealized absence of selection, mutation, migration and appreciable drift. These assumptions form a baseline for comparison with observations.
Random segregation and gamete union determine genotype proportions.
Epistasis means that the phenotypic effect associated with a locus depends on another locus, including masking effects in a biochemical pathway. Pleiotropy means that one gene can affect multiple traits. Penetrance describes the proportion or probability of the specified phenotype among carriers of a specified genotype in a defined context; expressivity describes the nature or degree of that phenotype. Genetic background, environment and age can influence genotype–phenotype relationships.
Allele transmission and phenotype realization answer distinct questions.
In the cellular DNA context, a gene is a genomic region encoding a functional RNA product, including an RNA that can be translated into protein. An allele is a sequence variant at a specified genomic location. Genotype describes the alleles or sequence state at the loci being considered; phenotype describes observable characteristics. At an ordinary diploid autosomal locus, matching allele copies are homozygous and different copies heterozygous. Phenotype also depends on genetic background, development and environment, so genotype and phenotype need not correspond one-to-one.
A stated locus and allele-copy model describe the genomic states segregated in the Mendelian model.