The law of independent assortment states that two or more genes assort independently that is, each pair of alleles segregates independently of any other pair of alleles during gamete formation. This law applies only to genes located on different loci either on different chromosomes (non-homologous) or on the same chromosome. This principle can be easily demonstrated in a dihybrid cross.
Dihybrid cross
It is a cross
between the two individuals that are hybrid (heterozygous) for two characters
e.g. seed shape and seed color (Round Yellow Seed – RrYy)
How do genes get separated?
Independent
assortment of genes occurs because of the presence of two different genes i.e.
gene for seed color and gene color either on non-homologous chromosomes or due
to crossing over (exchange of chromosomal segments in meiosis) in case the genes
are present on homologous chromosomes.
Example
P1 Generation: Mendel crossed true-bred plants for round seed shape and yellow seed color (genotype RRYY) with plants true-bred for the recessive condition, wrinkled seed shape, and green seed color. (genotype rryy).F1 generation: All Individuals of the F1 generation were hybrid (Heterozygous) for the dominant traits i.e. round seed shape and yellow seed color.
Self-fertilization of F1: Mendel self-fertilized F1 plants (RrYy). The F2 progeny included both parental phenotypes and also new varieties were obtained (recombinants), proving that genes for the shape and color have assorted independently.
Result:
Phenotypic ratio Round yellow: 9, Round green: 3, Wrinkled yellow: 3, Wrinkled green: 1
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