Allelic expression variation: the expression pattern or level of the alleles in the hybrids is different from that in the parents. This can also refer to the expression of homoeologous loci in interspecific hybrids.
Allopolyploid: an organism or individual that contains two or more sets of genetically distinct chromosomes, usually by hybridization between different species.
Amphidiploid: synonymous to allopolyploid. Contains a diploid set of chromosomes derived from each parent. Strictly speaking, only bivalents are formed in an amphidiploid, whereas multivalents are formed in an allopolyploid.
Aneuploid: an individual in which the chromosome number is not an exact multiple of the typical haploid set for that species.
Apomixis: only one parent (usually female) contributes genes to the offspring.
Autopolyploid: a polyploid created by the multiplication of one basic set of chromosomes (in one species).
Circadian: A circadian rhythm is a roughly 24-hour cycle in the biochemical, physiological, or behavioral processes of living organisms, including plants, animals, fungi, and cyanobacteria. The term “circadian” comes from the Latin circa, “around”, and diem or dies, “day”, meaning literally “approximately one day”. The study of biological temporal rhythms such as daily, tidal, weekly, seasonal, and annual rhythms is called chronobiology.
Circadian gating: The circadian clock controls certain physiological or behavioral events to occur during specific windows of the time while inhibiting them during others.
CONSTANS: A transcription factor that was first defined in Arabidopsis thaliana is central to the photoperiodic flowering response and senses day-length for rhythmic transcriptional
Cryptochrome: Blue light photoreceptors that regulate entrainment by light of the circadian clock in plants and animals.
Epiallele or Epigene: A gene or allele whose expression is controlled by DNA methylation or chromatin modification, without genetic mutation.
Epigenetics: The study of traits and gene expression changes that are independent of primary DNA sequences but dependent on DNA and chromatin modifications. Epigenetic traits are heritable and reversible.
Epigenetic memory: The set of DNA and chromatin modifications that are inherited through mitosis and meiosis to different cell types and/or subsequent generations in plants and animals.
Epistasis: The nonreciprocal interaction of nonallelic genes, which often refers to trans-acting relationship.
Flowering Locus C (FLC): a MADS-box gene responsible for inhibition of early flowering and in response to vernalization.
Flowering Locus T (FT): Encodes a protein responsible for initial stages of plant flowering. FT can serve as a mobile signal known as a major component of florigen.
Gametic imprinting: the expression of a gene is dependent on its parental origin in the offspring.
Genome shock: The term first coined by Barbara McClintock to describe rapid genomic changes largely associated with activation of transposable elements in interspecific hybrids. The phenomenon is commonly defined as epigenetic modifications and (nonadditive) gene expression changes due to intergenomic interactions in interspecific hybrids and allopolyploids.
Heterosis: the greater vigor of growth, survival, and fertility in hybrids than in the parents.
Homoeologs: chromosomes or genes in related species that are derived from the same ancestor and coexist in an allopolyploid.
Homologs: genes or structures that share a common evolutionary ancestor.
Homoploid hybrids: hybrids formed between different species, in some cases, resulting in a derivative hybrid species without a change in chromosome number.
Imprinting or genomic imprinting: unequal expression of maternal and paternal alleles in the offspring.
Inheritance of Acquired Characters: The theory proposed by Lamarck that if an organism changes during life in order to adapt to its environment, those changes are passed on to its offspring. The theory does not provide any basis or experimental evidence for inheritance.
Nonadditive gene expression: the expression level of a gene in an allotetraploid is not equal to the sum of two parental loci (1 + 1 ≠ 2), leading to activation (>2), repression (<2), dominance, or overdominance. There is an epigenetic basis for nonadditive gene expression.
Nucleolar dominance: An old epigenetic phenomenon that describes silencing or activation of one parental set of rRNA genes in an interspecific hybrid or allopolyploid of plants and animals.
Orthologs: chromosomes or genes in different species that have evolved from the same ancestor.
Paralogs: two or more genes in the same species that share a single ancestral origin.
Paramutation: An epigenetic phenomenon that was discovered in maize and sorghum where one allele influences expression of the other allele at the same locus when two alleles are combined in a hybrid (heterozygote). The first allele is defined as paramutagenic, and the second allele as paramutable. Paramutated alleles display transgenerational inheritance and can be metastable.
Photomorphogenesis: Changes in plant growth, development, and differentiation in response to the duration and nature of light, independent of photosynthesis.
Photoperiodism: The response of organisms to seasonal changes of light, resulting in physiological and/or developmental activities such as flowering in plants. The pathway is known as photoperiodic flowering.
Phytochrome: The molecules responsible for the photoperiodic control of flowering.
Ploidy: the number of basic chromosome sets.
Polyploidy: A situation where the number of chromosome sets is greater than two. A polyploid refers to a cell or organism having more than two sets of chromosomes. Polyploids can be classified into autopolyploids, allopolyploids, and paleopolyploids. An autopolyploid originates by the multiplication of one basic set of chromosomes, while an allopolyploid results from combination of distinct sets of chromosomes often through interspecific hybridization followed by chromosome doubling or fusion of unreduced gametes.
Pseudo-inheritance: A pseudo-science and political ideology proposed by Lysenko that rejects natural selection and Mendelian genetics; it was proposed to increase wheat crop yield by cold and humidity, a process known as vernalization, and further to change durum (tetraploid) wheat to bread (hexaploid) wheat. The political movement of Lysenkoism was a tragedy for science and society in former Soviet Union countries and their affiliated institutions.
Transgenerational epigenetic inheritance: A phenomenon of non-genetic patterns that are transmitted from one generation to another and in some instances from grandparents to grandchildren.
Vernalization: The process that plants require a period of cold temperature for seed germination and flowering.
X-chromosome inactivation: One of the two X chromosomes in mammalian females is repressed in somatic cells as a mechanism of dosage compensation (compared to a single X chromosome in males). The inactivated X chromosome is reversible during reproductive stage to produce eggs. This epigenetic phenomenon is stable and heritable from mothers to daughters.
