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HELLO STUDENTS: DAY- 33 Morning

                              PRINCIPLES OF INHERITANCE AND VARIATION

 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.

         

Mr. A. KINGSLIN M.Sc, BEd, Phd,(doing)
Post Graduate Teacher in Botany
St. Mary Goretty Hr. Sec School, Manalikarai 
Kanyakumari district





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