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Law of Independent Assortment (The "Second Law")

The Law of Independent Assortment, also known as "Inheritance Law", states that alleles of different genes assort independently of one another during gamete formation. While Mendel's experiments with mixing one trait always resulted in a 3:1 ratio (Fig. 1) between dominant and recessive phenotypes, his experiments with mixing two traits (dihybrid cross) showed 9:3:3:1 ratios (Fig. 2). But the 9:3:3:1 table shows that each of the two genes are independently inherited with a 3:1 ratio. Mendel concluded that different traits are inherited independently of each other, so that there is no relation, for example, between a cat's color and tail length. This is actually only true for genes that are not linked to each other.

Independent assortment occurs during meiosis I in eukaryotic organisms, specifically metaphase I of meiosis, to produce a gamete with a mixture of the organism's maternal and paternal chromosomes. Along with chromosomal crossover, this process aids in increasing genetic diversity by producing novel genetic combinations.

Of the 46 chromosomes in a normal diploid human cell, half are maternally-derived (from the mother's egg) and half are paternally-derived (from the father's sperm). This occurs as sexual reproduction involves the fusion of two haploid gametes (the egg and sperm) to produce a new organism having the full complement of chromosomes. During gametogenesis - the production of new gametes by an adult - the normal complement of 46 chromosomes needs to be halved to 23 to ensure that the resulting haploid gamete can join with another gamete to produce a diploid organism. An error in the number of chromosomes, such as those caused by a diploid gamete joining with a haploid gamete, is termed aneuploidy.

In independent assortment the chromosomes that end up in a newly-formed gamete are randomly sorted from all possible combinations of maternal and paternal chromosomes. Because gametes end up with a random mix instead of a pre-defined "set" from either parent, gametes are therefore considered assorted independently. As such, the gamete can end up with any combination of paternal or maternal chromosomes. Any of the possible combinations of gametes formed from maternal and paternal chromosomes will occur with equal frequency. For human gametes, with 23 pairs of chromosomes, the number of possibilities is 223 or 8,388,608 possible combinations.[3] The gametes will normally end up with 23 chromosomes, but the origin of any particular one will be randomly selected from paternal or maternal chromosomes. This contributes to the genetic variability of progeny.
His experiments with the breeding of plants such as peas

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Related Questions

In which generation were recessive traits hidden in all plants in mendels experiment?

f2 generation


What mendels' theory of transfer of traits?

mendel theory transfer of traits


The traits in mendels pea plant study were inherited?

Yes, Mendel observed that certain traits in his pea plant study were consistently passed down from one generation to the next, indicating that they were inherited in a predictable manner according to his laws of inheritance.


What is mendels theory of the transfer of traits?

Mendel's theory of the transfer of traits, also known as Mendelian inheritance, states that genetic traits are determined by the inheritance of alleles from parents. These alleles segregate independently during gamete formation and randomly combine during fertilization, resulting in offspring with specific traits based on the combinations of alleles inherited.


What was the original generation of pea plants in mendels experiment?

P1 or parental


What did all the traits Mendels tested have in common?

All the traits that Mendel tested had clearly dominant forms.


What is Mendels's ratio for dominant to recessive traits?

The Ratio is 3:1


In which generation were recessive traits in all the plants in mendels experiments?

F1 generation


In which generation were recessive traits visible in a few plants in mendels?

F2 generation


Which generation were recessive traits hidden in all the plants in mendels experiments?

F1 generation


Why were color and seed shape in pea plants good traits for Mendels to study?

sex


In which generation were recessive traits visible in a few plants in mendels experiments?

F2 generation