5. PRINCIPLES OF INHERITANCE AND VARIATION
IMPORTANT TERMS
- Genetics: Study of inheritance, heredity and variation of characters or Study of genes and chromosomes.
- Inheritance: Transmission of characters from parents to progeny. It is the basis of Heredity.
- Variation: Difference between parents and offspring.
- Character: A heritable feature among the parents & offspring. E.g. Eye colour.
- Trait: Variants of a character. E.g. Brown eye, Blue eye.
- Allele: Alternative forms of a gene. E.g. T (tall) and t (dwarf) are two alleles of a gene for the character height.
- Homozygous: The condition in which chromosome pair carries similar alleles of a gene. Also known as pure line (True breeding). E.g. TT, tt, YY, yy etc.
- Heterozygous: The condition in which chromosome pair carries dissimilar alleles of a gene. E.g. Tt, Yy etc.
- Dominant character: The character which is expressed in heterozygous condition. It indicates with capital letter.
- Recessive character: The character which is suppressed in heterozygous condition. It indicates with small letter.
- Phenotype: Physical expression of a character.
- Genotype: Genetic constitution of a character.
- Hybrid: An individual produced by the mating of genetically unlike parents.
- Punnett square: A graphical representation to calculate probability of all genotypes of offspring in a genetic cross.
MENDEL’S
LAWS OF INHERITANCE
Gregor Mendel is the Father of genetics.
He conducted some hybridization experiments on garden peas (Pisum sativum) for 7 years (1856-1863).
Steps in making a cross (Deliberate mating) in pea:
Mendel selected 7 pairs of true breeding pea varieties:He conducted some hybridization experiments on garden peas (Pisum sativum) for 7 years (1856-1863).
Steps in making a cross (Deliberate mating) in pea:
- Selection of 2 pea plants with contrasting characters.
- Emasculation: Removal of anthers of one plant to avoid self-pollination. This is female parent.
- Pollination: Collection of pollen grains from the male parent and transferring to female parent.
- Collection & germination of seeds to produce offspring.
|
7 Characters |
Contrasting Traits |
|
|
Dominant |
Recessive |
|
|
1. Stem height |
Tall |
Dwarf |
|
2. Flower colour |
Violet |
White |
|
3. Flower position |
Axial |
Terminal |
|
4. Pod shape |
Inflated |
Constricted |
|
5. Pod colour |
Green |
Yellow |
|
6. Seed shape |
Round |
Wrinkled |
|
7. Seed colour |
Yellow |
Green |
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