PRNCIPLES OF INHERITANCE OVERVIEW POINTS

Genetics: Study of heredity and variation.

Heredity: Inheritance of characters transmitted from parents to offsprings.

Variation: Degree by which progeny differ from their parents.

Father of genetics- Gregor Johann Mendel.

He conducted experiments in garden pea(Pisum sativam)

Reasons for selecting garden pea,

1.Bisexual flower.
2.Self and cross pollination takes place.
3.Contrasting pairs of characters.
4.Short life span.

There is a particular gene for a particular character.

For indicating a gene ,there are two alleles.

Experiment

1.True breeding

(Producing same character from same plants by producing them for 3-4 generation,made them pure for that specific character)

By self pollination,he created two pure breeding Tall and a pure breeding dwarf.

A character has two forms a dominant and a recessive form.

For example Height has two forms one is Tall and the other is dwarf.

2.A pure breeding Tall is crossed with a pure breeding dwarf.

At the time of gamete formation,the two factors separate or segregate.
The next generation is known as F1 generation or first filial generation.

In F1 generation, Dominant character T is expressed.
And T is completely dominant over t -- complete dominance.
Thus it expresses tallness.
This observable character is called phenotype.The genetic constitution is called genotype.

3.Then the F1 generation is self polinated.
Tt*Tt
At gamete formation,both alleles segregate,
TT Tt Tt tt are formed
Phenotype - 3 tall and 1 short is formed.

Genotype - 3genotype TT Tt tt
Phenotypic ratio-3:1
Genotypic ratio-1:2:1

Monohybrid cross-The character of one is crossed.

Reginald C Punnett brought a square called Punnett square or check board for easily finding the phenotype and genotype.

Test cross-A cross between F1 hybrid and its r
Monohybrid test cross ratio-1:1
Dihybrid test cross ratio-1:1:1:1

Incomplete dominance- The phenomenon which occurs when in a cross made between a dominant and a recessive ,the F1 offspring do not show dominant trait but are intermediate between dominant and recessive.
Codominance-The phenomenon by which both the alleles in a heterozygote express themselves.
Multiple alleles-Genes having more than one alleles in a population.
Pleiotropy-The ability of a gene to have many effects.
Polytene chromosomes-Large sized chromosomes

Linkage-The phenomenon of co existence of two or more genes in the same chromosome.

Recombination-The reshuffling of the parental genes into new combinations.

Recombinant-The product of recombination.

Crossing over-The phenomenon by which exchange of segments takes place between non sister chromatids of homologous chromosomes.

Chromosome map-A linear graphic representation of the sequence and relative distances of the various genes present in the chromosome.

Chromosome mapping-The method of preparing maps of a species.

Mutation-The sudden heritable change in the genotype of an organism.

Mutants-The individuals showing mutations.

Muton-The smallest segment of DNA which can undergo mutation.

Chromosomal aberrations-The structural changes in a chromosome.

Point mutation-Mutation which arises due to change in a single base pair of DNA.

Mutagens-The physical and chemical factors which bring about mutations.

Pedigree analysis-An analysis of traits in several generations of s family.

Pedigree-The ancestral history in an individual.

Proband-The person from whom case history of the pedigree starts.

Proposity-Male pro band.

Proposita-Female pro band

Mendelian disorders-Genetic disorders caused due to alteration or mutation in single gene.

Phenylpyruvic idiots-Persons with phenylketonuria.

Chromosomal disorders-Genetic disorders caused due to absence or excess or abnormal arrangement of one or more chromosomes.

Ploidy-The numerical changes of chromosomes.

Polyploidy-Occurence of more than two genomes.

Euploidy-The numerical changes of chromosomes in genome level.

Aneuploidy-The numerical changes of chromosomes at an individual level.

Trisomy-2n+1 condition

Monosomy-2n+1condition