Genetics : It is the science of heredity and the principles governing the inheritance of characters from parent to the progeny i.e., offspring is called genetics.
Heredity : The process by means of which characters are transmitted from parent to the offspring is called heredity.
Mendelism : Mendel’s peas experiment, valid analysis and deduction of laws of inheritance are collectively called Mendelism.
Gene : Genes are the functional heredity units which determine a biological character of an organism.
Mutation : Mutation is defined as the permanent change in the hereditary materials.
Locus : A specific gene of a specific chromsome present in a specific part is called the locus of that particular gene.
Alleles or Allelomorphs : Contrasting pairs of different characters having the same locus in the homologous chromosomes are known as allelomorphs.
Homozygous and heterozygous : An individual having only one allelle or in other words two identical genes affecting a trait is known as homozygous.
Phenotype : Whatever characteristics of an organism are visible, are called phenotype.
Genotype : The genetic materials inherited by an organism from parents is called genotype and therefore represents the genetic constitution or breeding behaviour of an organism.
Monohybrid cross : When in a cross one pair of contrasting characters (a pair of alleles) is considered at a time, then such a cross is known as monohybrid cross. e.g. cross between a tall (TT) and dwarf (tt) pea plants.
Dihybrid cross : When in a cross two pairs of contrasting characters are considered at a time, then such cross is known as dihybrid cross. e.g. cross between two pea plants with yellow smooth and green wrinkled seeds.
Dominant and Recessive : These are two important characterstics. The trait which appears in the first filial or F, generation even though the other trait or factor is present after crossing two pure varieties of plants, is known as dominant. The other character which remains in suppressed condition and does not appear is known as recessive.
Backcross : The F, individuals are obtained after crossing a variety carrying a particular trait with another variety carrying its contrasting trait (i.e., from parental generation). The cross of F1 individual with either of the two parents is known as backcross.
Testcross : When plants obtained in F1 generation is backcrossed with the dominant phenotype parent then in the progeny no recessive individuals are obtained. But when plants of F1 generation is backcrossed with the recessive parent then in the progeny both the phenotypes will appear. When only the cross is done with recessive parent then it is called testcross. It is used to test whether an individual is pure (homozygous) or hybrid (heterozygous).
Homologous chromosome : There are two sets of chromosomes in zygote of all sexually reproducing organisms and all cells derived from this by mitosis. The two sets are contributed by the two parents. Every member of a set contributed by one parent has a counterpart in the other set of chromosomes contributed by other parent. These similar chromosomes are called homologous chromosomes.
Reciprocal cross : Two same parents are crossed in such a way that if in one experiment say ‘A’ is used as female parent and ‘B’ as male parent, in the other experiment ‘A’ will be used as male parent and ‘B’ as female parent. Utility of such crosses is to find out whether equal contribution of characters are made by both the parents.
Hybridisation : Between two genetically unlike parents, hybridisation is a cross often restricted to offspring of two different species, or well marked varieties of same species.
Self fertilisation : Self fertilisation takes place as a result of union between male gamete of pollen of a flower with female gamete or egg of ovary of same flower.
Cross fertilisation : This type of fertilisation takes place between male gamete of a pollen of a flower with female gamete or egg of ovary of another flower.
Mendel’s Laws
Law of Segregation : This is the first law of Mendel. It states that “allelic genes (factors of contrasting character) in a zygote do not blend or contaminate each other but segregate and pass into different gametes.”
Law of Independent Assortment : This is the second law of Mendel. It states that the different pair of alleles assort in an independent manner and segregate from each other.
Mendel’s Monohybrid Cross : This is the third law of Mendel. A cross between two parents of which a variety carrying a particular trait or character with another variety carrying its contrasting trait or chatacter is termed as monohybrid cross.
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