139
Question
Explain Mendelism and Laws of Inheritance with examples.
Explain Mendelism and Laws of Inheritance with examples.
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Solution
Law of Dominance characters are controlled by discrete units called factors, which occur in pairs with one member of the pair dominating over the other in a dissimilar pair. This law explains expression of only one of the parental character in F1 generation and expression of both in F2 generation.
Law of Segregation
This law states that the two alleles of a pair segregate or separate during gamete formation such that a gamete receives only one of the two factors.
In homozygous parents, all gametes produced are similar; while in heterozygous parents, two kinds of gametes are produced in equal proportions.
Lets study the following cross that considers only a single character (e.g., height of the part)
Studying the cross:
TT, tt, and Tt are genotypes while the traits, tall and dwarf, are phenotypes.
T stands for tall trait while t stands for dwarf trait.
Even if a single ‘T’ is present in the genotype, phenotype is ‘tall’. When ‘T’ and ‘t’ are present together, ‘T’ dominates and suppresses the expression of ‘t’. Therefore, T (for tallness) is dominant trait while t (for dwarfness) is recessive trait.
TT and tt are homozygous while Tt is heterozygous.
From the cross, it can be found that alleles of parental pair separate or segregate from each other and only one allele is transmitted to the gamete.
Gametes of TT will have only T alleles; gametes of tt will have only t alleles, but gametes of Tt will have both T and t alleles.
Law of independent Assortment
When two pairs of traits are combined in a hybrid, one pair of character segregates independent of the other pair of character. In a dihybrid cross between two plants having round yellow (RRYY) and wrinkled green seeds (rryy), four types of gametes (RY, Ry, rY, ry) are produced. Each of these segregate independent of each other, each having a frequency of 25% of the total gametes produced.
Law of Dominance characters are controlled by discrete units called factors, which occur in pairs with one member of the pair dominating over the other in a dissimilar pair. This law explains expression of only one of the parental character in F1 generation and expression of both in F2 generation.
Law of Segregation
This law states that the two alleles of a pair segregate or separate during gamete formation such that a gamete receives only one of the two factors.
In homozygous parents, all gametes produced are similar; while in heterozygous parents, two kinds of gametes are produced in equal proportions.
Lets study the following cross that considers only a single character (e.g., height of the part)
Studying the cross:
TT, tt, and Tt are genotypes while the traits, tall and dwarf, are phenotypes.
T stands for tall trait while t stands for dwarf trait.
Even if a single ‘T’ is present in the genotype, phenotype is ‘tall’. When ‘T’ and ‘t’ are present together, ‘T’ dominates and suppresses the expression of ‘t’. Therefore, T (for tallness) is dominant trait while t (for dwarfness) is recessive trait.
TT and tt are homozygous while Tt is heterozygous.
From the cross, it can be found that alleles of parental pair separate or segregate from each other and only one allele is transmitted to the gamete.
Gametes of TT will have only T alleles; gametes of tt will have only t alleles, but gametes of Tt will have both T and t alleles.
Law of independent Assortment
When two pairs of traits are combined in a hybrid, one pair of character segregates independent of the other pair of character. In a dihybrid cross between two plants having round yellow (RRYY) and wrinkled green seeds (rryy), four types of gametes (RY, Ry, rY, ry) are produced. Each of these segregate independent of each other, each having a frequency of 25% of the total gametes produced.
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