📖Breeding Terminology: Essential Glossary for Exams

Why Terminology Matters

In competitive exams (IBPS AFO, NABARD, ICAR JRF, RRB SO), one-liner questions on breeding terminology are among the highest-frequency question types. Knowing the precise definitions — and distinguishing between similar-sounding terms like heterosis vs. luxuriance, or synthetic vs. composite — can make the difference between a correct and incorrect answer.

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A comprehensive glossary of exam-critical breeding and genetics terms frequently asked in IBPS-AFO, NABARD, ICAR-JRF, and RRB-SO examinations. Each term includes its precise definition and exam context.

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Pollination & Reproduction Terms

• Duodichogamy — individual plants produce two batches of male flowers temporally separated by female flowers. Rarest temporal sexual system in flowering plants. (Asked in RRB SO 2019)

• Geitonogamy — pollen from one flower of a plant falls on the stigma of another flower of the same plant. Functionally cross-pollination but genetically self-pollination. E.g. Maize.

• Xenogamy — transfer of pollen from a flower of one plant to the stigma of a flower of a different plant. This is true cross-pollination and leads to maximum genetic recombination.

• Emasculation — removal of stamens or anthers, or killing of pollen grains, to prevent self-pollination. Essential step in hybridization of bisexual flowers. Methods include hand emasculation, hot water treatment, alcohol treatment, and use of gametocides. (AFO-2023)

• Parthenocarpy — development of fruit without fertilization. The resulting fruits are seedless. E.g. Banana, Seedless watermelon.

• Agamospermy — development of embryo and seed without meiosis and fertilization. A form of apomixis where seeds are produced asexually. E.g. Citrus, Mango.

• Apomixis — reproduction through seeds formed without fusion of gametes (without sexual union). It includes agamospermy, adventitious embryony, and apospory.

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Genetic Variation Terms

• Allosyndesis — pairing of non-homologous chromosomes from diverse sets of an allopolyploid at meiosis. Results in recombination between genomes of different species. (RRB SO-2019)

• Autosyndesis — pairing of homologous chromosomes from similar sets of an allopolyploid at meiosis. Results in recombination within genomes of the same species.

• Genepool — sum total of all alleles present in the breeding/reproductive members of a random mating population. Classified into:

  • Primary genepool — same species, cross easily
  • Secondary genepool — related species, cross with some difficulty
  • Tertiary genepool — distantly related, cross with extreme difficulty (embryo rescue needed)

• Gene frequency — proportion of one allele relative to all alleles of a gene in a Mendelian population. Also called allele frequency.

• Biodiversity — total variability present within and among species of all living organisms. Includes genetic, species, and ecosystem diversity.

• Epistasis — when one gene affects the expression of another non-allelic gene. Types include dominant epistasis (12:3:1), recessive epistasis (9:3:4), duplicate epistasis (15:1), complementary epistasis (9:7), and inhibitory epistasis (13:3).

• Pleiotropism — one gene affects more than one character (pleiotropic genes). E.g. the gene for seed coat colour in peas also affects flower colour and leaf axil pigmentation.

• Silent Mutation — a mutation that changes the nucleotide sequence but does not alter the amino acid or protein activity due to the degeneracy of the genetic code.

• Spontaneous Mutations — mutations occurring under natural conditions without any deliberate treatment with mutagens. Frequency is very low (10^-5 to 10^-8 per gene per generation).

• Tautomerism — ability of a molecule (especially bases of DNA) to exist in more than one chemical form. Tautomeric shifts in bases lead to transition mutations during DNA replication.

• Pseudo alleles — genes that govern different expressions of the same character, are closely linked, and exhibit cis-trans position effect. They can be separated by crossing over. E.g. Star and asteroid loci in Drosophila.

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Breeding & Selection Terms

• Heterosis (Hybrid Vigour) — superiority of F1 hybrid in one or more characters over its parents. Term coined by G.H. Shull (1914). Three types:

  • Relative heterosis — F1 superiority over mid-parent value
  • Heterobeltiosis — F1 superiority over the better parent
  • Standard/Economic heterosis — F1 superiority over the best commercial check variety

• Heterobeltiosis — heterosis estimated over the superior/better parent. More useful than mid-parent heterosis for practical breeding purposes.

• Luxuriance — superiority of F1 over parents in vegetative growth but NOT in yield and adaptation. Also known as pseudo heterosis. The hybrid may look vigorous but performs poorly in reproductive traits.

• Top cross — cross between an inbred line and an open-pollinated variety. Also known as inbred-variety cross. Used to evaluate general combining ability (GCA) of inbred lines. Proposed by Davis (1927).

• Inbreeding — mating between individuals related by descent or common ancestry (brother-sister/sib mating). Highest degree of inbreeding is achieved by selfing. Increases homozygosity by 50% per generation in self-pollinated crops.

• Inbreeding Depression — severe reduction in vigour and fertility in cross-pollinated species when subjected to continued selfing. Very low in self-pollinated crops. Highest in cross-pollinated crops like Carrot, Alfalfa, Lucerne. Opposite of heterosis.

• Acclimatization — adaptation or adjustment of an introduced variety to a new environment. Different from adaptation, which is a natural evolutionary process.

• Synthetic Variety — produced by crossing in all combinations a number of lines that combine well, followed by open pollination. Can be grown for 4-5 years without significant yield reduction. Reconstituted from parental lines when yield drops. Proposed by Sewall Wright.

• Composite Variety — produced by mixing seeds of several phenotypically outstanding lines and encouraging open pollination. Broader genetic base than synthetic varieties but may show faster yield decline over generations.

• Land races — crop cultivars developed through traditional farming over centuries of natural and human selection. Good source of genetic variability and adaptation genes. Also called desi varieties or primitive cultivars.

• Obsolete varieties — varieties developed by systematic modern agricultural science that have been replaced by newer, improved varieties. Valuable as sources of specific genes.

• Chimera — an individual with one genotype in some parts and another genotype in other parts. Arises from mutation in a single cell during development. Jaganath rice = gamma-ray induced semi-dwarf mutant from T-141. Types include sectorial, mericlinal, and periclinal chimeras.

• Amphidiploid — an allopolyploid with two complete copies of each parental genome, behaves as a diploid during meiosis (showing bivalent pairing). Used as a bridge species for character transfer between incompatible species. E.g. Raphanobrassica (2n = 36) — first artificial amphidiploid produced by Karpechenko (1927).

• Ideotype — according to Donald (1968), a biological model that is expected to perform or behave in a predictable manner within a defined environment. Ideotype breeding aims to combine specific morphological and physiological traits for maximum yield.

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Cytogenetics & Molecular Terms

• Cytogenetics — study of various aspects of chromosomes and their effects on the development of characters. Bridges the gap between cytology and genetics.

• Genomics — study of the structure and function of the entire genome of an organism. Includes structural genomics, functional genomics, and comparative genomics.

• Genome — complete set of chromosomes of a diploid species (one haploid set). Represented by letters (e.g. Wheat: AABBDD = 3 genomes).

• Euphenics — deals with the control of hereditary diseases, especially inborn errors of metabolism, through environmental manipulation or medical intervention. Term coined by Lederberg.

• Allele — alternate form of a gene occupying the same locus on homologous chromosomes. Shorter term for allelomorph.

• Multiple alleles — the presence of many alleles of a single gene in a population (but only two per diploid individual). E.g. ABO blood group system has three alleles: I^A, I^B, i.

• Antibody — a protein (immunoglobulin) found in serum or plasma, demonstrated by specific reaction with its corresponding antigen. Produced by B-lymphocytes.

• Antigen — a substance that induces production of a specific antibody when introduced into a vertebrate body. Located on the surface of RBC (in blood group systems).

• Cytoplasmic inheritance — characters controlled by plasmagenes (genes in cytoplasm — mitochondria, chloroplasts). Also called extranuclear or maternal inheritance. Always shows maternal effect. E.g. Male sterility in maize, Kappa particles in Paramecium.

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Important Historical Facts

• First artificial hybrid in plants: Thomas Fairchild (1717) — crossed Sweet William (Dianthus barbatus) with Carnation (Dianthus caryophyllus). The resulting hybrid is known as Fairchild’s Mule.

• Back cross — crossing F1 with one of its parents. Important in development of disease resistance through backcross breeding. Two types:

  • Recurrent parent — the parent to which repeated backcrosses are made
  • Donor parent — the parent that donates the gene of interest

• Test cross — crossing F1 (or any dominant phenotype individual) with its homozygous recessive parent. Used to determine the genotype of a dominant phenotype individual. Proposed by Mendel.

• Pure line theory — given by Johannsen (1903). A pure line is the progeny of a single homozygous self-pollinated plant. Selection within a pure line is ineffective.

• Law of Homologous Series — given by N.I. Vavilov (1920). Species that are genetically related exhibit parallel variation in their characteristics.

• Mutation theory — given by Hugo de Vries (1901) based on his work on Oenothera lamarckiana (Evening Primrose). However, what he observed were actually chromosomal aberrations, not gene mutations.

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