IMPORTANT TERMS:
· Allele:Two genes (Mendelian factors), which occur on the same locus in homologous chromosomes and control the expression of a trait in an individuals.( Previously the term ‘alleles’ was used for the alternative forms of a gene which determine contrasting characters).
· Aneuploidy: A condition of having fewer or extra chromosomes than the normal genome number of a species.
· Autosomes: Chromosomes other than the sex chromosomes are called autosomes. They are similar in both males and females.
· Back Cross: A cross between an individual offspring and one of its parents.
· Carrier: A heterozygous individual which is phenotypically normal but carries allele for the defective trait.
· Chiasmata: The points where non sister chromatids of paired homologous chromosomes physically cross-over.
· Clone: Genetically identical individuals (Individuals which are carbon copy of each other and that of parents).
· Co -dominance: Expression of both the alleles in a heterozygous condition ( equal dominance of both the alleles).
· Colchicine: A chemical (obtained from the roots of Colchicum autumnale) that arrests the mitotic divison.
· Complementary Genes: Non allelic genes which are complementary of one another in dominant state in the expression of a trait.
· Dihybrid Cross: A cross in which inheritance of two pairs of contrasting factors/genes is studied simultaneously.
· Dominant Allele: The allele that expresses itself in the homozygous as well as heterozygous condition.
· Epistasis: Phenomenon by which a gene suppresses the phenotypic expression of a non-allelic gene.
· Euploidy: A condition of having more than two sets of chromosomes.
· Extranuclear Genes: The genes present outside the nucleus like the ones present in mitochondria and plastids.
· Gene:A basic unit of heredity.
· Genotype:Genetic constitution of an organism.
· Heterozygous:A condition when an organism has different allelic forms of a gene.
· Homozygous:A condition when an organism has same allelic forms of a gene.
· Hybrid: An offspring produced from a cross between two individuals of the same species that differ from each other at least in one trait.
· Karyotype: An arrangement given to the chromosomes of a species according to their size, position of centromere and banding pattern.
· Linkage Group: The group of genes situated on the same chromosome constitutes a linkage group.
· Linkage: The phenomenons due to which the genes present on the same chromosome tend to inherit together in the same gamete.
· Locus:A position on a chromosome where an allele is located.
· Monohybrid Cross: A cross in which inheritance of one gene pair of contrasting factor/gene is studied.
· Multiple Alleles: More than two forms of a gene which express a particular trait.
· Mutagens:Any chemical or a physical agent that causes mutations.
· Non-disjunction:A condition when two chromosomes of a particular homologous pair fail to separate during meiosis.
· Offspring:Individuals produced as a result of sexual reproduction.
· Pedigree Analysis: A system to analyse the distribution and movement of traits in the family tree.
· Phenotype:Expressed or observable characteristics of an organism.
· Pleiotropy:Multiple effects of a gene on the phenotype of an organism.
· Polygenic Inheritance: Inheritance of a trait in which dominant polygene have cumulative or additive effect. (It is also called quantitative inheritance).
· Progeny:Organisms produced as a result of a cross.
· Punnett square: A checker board used to depict the results of a cross.
· Pure Line: True breeding individuals which have been derived homozygous parents through self breeding.
· Recessive Allele: An allele which fails to express itself in the presence of its contrasting allele.
· Reciprocal Cross: A cross where gametes from parental generation are reversed.
· Sex Chromosomes: The chromosomes that determine the sex of an individual organism are called sex chromosomes or allosomes.
· Test Cross: A cross between an unknown genotype and the homozygous recessive individual for the same trait.
· Trait:Any recognizable feature of an organism.
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