Page 398 - General Knowledge

GENERAL KNOWLEDGE 2019

Law of Segregation

 Based on the fact that the alleles do not blend, both the characters are recovered in F2
generation, not seen on F1 stage.
 Although the parents contain two alleles during gamete formation, alleles of a pair segregate
from each other; gamete receives only one of the two factors.
 Homozygous parent produces all gametes.
 Heterozygous produces two kinds of gametes, each having one allele with equal proportion.

Law of Independent Assortment
 In the dihybrid cross, phenotypes round, yellow, wrinkled, yellow, round, green and wrinkled.
Green appears in the ratio 9:3:3:1.
 This law states that, ―When two pairs of traits are combined in a hybrid cross, segregation of
one pair of characters is independent of the other pair of characters‖.

Monohybrid Inheritance
 Mendel crossed one tall and short pea plant and a tall plant was formed.
 He called the First generation F1 and the offspring he called F1 progeny.
 He then obtained the second generation by crossing F1 progeny with parent plants.
 Resulted in both tall and short plants in a ratio of 3:1.
 The traits absent in F1 generation had reappeared in F2 generation.
 Suppressed traits as recessive traits and expressed traits as dominant traits.
 These are observed as Law of dominance and Law of segregation.

Dihybrid Inheritance
 Mendel took two traits together for crossing i.e. color and shape of feeds.
 Selected round yellow seed and wrinkled green seed and crossed them.
 Obtained only round yellow seeds in the F1 generation.

 F1 progeny was self-pollinated, gave four different combinations of seeds.
 They are round - yellow, wrinkled - yellow, round green and wrinkled green seeds in F2
generation.
 Concluded as characters are distributed and inherited independently.
 These are observed as third law as Law of Independent Assortment.
Terms in Genetics
 Gene: Part of DNA that carries hereditary information passed from parents to children.

 Allele: Different forms of a gene that produces variation in genetically inherited trait.
 Homozygous: Having identical alleles of the same gene.
 Heterozygous: having different alleles for the same gene where one allele is dominant
while the other is recessive.
 Dominant: Even in the presence of two allelic forms of a gene, one masks the contributions
of the other.
 Recessive: These genes are expressed in the offspring only when inherited from both
parents.
 Genotype: Internal heredity information comprising the genetic code.
 Phenotype: Outwardly expressed traits.

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