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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