Mendel's Law of Independent Assortment: Dominance, Segregation

The Mendelian Law of Independent Assortment explains how genes for different traits are inherited independently of each other. Discovered by Gregor Mendel through his experiments with pea plants, this law states that the inheritance of one trait does not influence the inheritance of another, as long as the genes are on different chromosomes. In this article, the law of independent assortment, Mendel's experiments, Mendel's law of independent assortment, and the mechanism behind independent assortment, are discussed. The Law of Independent Assortment is a topic of the chapter Principles of Inheritance and Variation in Biology.

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This Story also Contains

1. What is the Law of Independent Assortment?
2. Mendel's Experiments
3. Mendel's Law of Independent Assortment
4. Mechanism behind Independent Assortment

What is the Law of Independent Assortment?

Mendel is accredited for making significant studies with the help of pea plants in mid - the 19th century that entail the contemporary idea of heredity. His systematic and detailed observations and mathematical computations gave out fundamental principles which are known as Mendel’s laws of inheritance.

The principle that came from Mendel’s pea plant experiment was the Law of Independent Assortment which showed that alleles relating to different traits do not influence each other during the formation of gametes, this fundamental knowledge regarding genetic variation and inheritance was a breakthrough. This realization is essential in present-day genetics to the initiative and calculation of genetic relation, appraisal of substituting genetic consequences, and promotion of benevolent sectors such as farming and medicament through selection and biotechnology.

Mendel's Experiments

Gregor Mendel’s studies with the help of pea plants in the middle of the nineteenth century can be considered the beginning of genetics studies. Mendel meticulously studied seven distinct traits in pea plants: It also examines seed shape (round or wrinkled), seed colour (yellow or green), pod shape (inflated or constricted), pod colour (green or yellow), flower colour (purple or white), the position of the flower (axial or terminal) stem height length (tall or short ).

To understand the patterns of inheritance, Mendel used dihybrid cross–breeding in which two different traits are followed at the same time. Hence, the different crosses included by Mendel include: For instance, in one experiment, he only crossbred plants of peas with both round seeds and yellow seeds with the other being wrinkled green seeds.

Thus, the ratios of phenotypes in the offspring known as F2 generation exposed the Law of Independent Assortment according to Mendel. This law was formulated to explain that loci for different genes behave independently of each other indicating that genes controlling different characteristics are passed on independently, although it is possible to experience ‘linkage’ if genes are located on the same chromosome. Mendel’s consistent and accurate experimentations and subsequent analyses laid the base of what came to be known as Mendelian genetics, which indeed had the most significant impact on the field of biology and basal knowledge of genetic transmission in species.

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Mendel's Law of Independent Assortment

The Law of Independent Assortment is that alleles for different genes, thus the traits they control, are sorted independently of each other in the formation of gametes. What this means is that one character is not inherited together with another character if the genes for these characters are on different chromosomes or sufficiently far apart on the same chromosome so that they assort independently.

Explanation of how this Law differs from The Law of Segregation

The Law of segregation which was proposed by Mendel earlier suggest that the two alleles of a trait separate during the gamete formation and are randomly distributed between each of the gametes. This law concerns only one gene and shows that the offspring receives one allele of a gene from each parent for that particular trait.

Illustration of the Concept using a Dihybrid Cross (Eg., Seed Shape and Seed Colour)

Let us also use the Law of Independent Assortment to explain the following dihybrid cross: between the pea plant with round yellow seeds RRYY and the pea plant with wrinkled green seeds dry. According to Mendel's experiments:

The F1 generation of this cross will consist of all F1 hybrids which will be heterozygous for both the traits, RrYy.

If these plants are self-crossed (F2 generation), the factors for seed shape (Rr), as well as seed colour (Yy), and dims will segregate independently during gamete formation.

This results in a 9:Therefore, there will be a 3:3:1 phenotypic ratio in the offspring, where:

• 9 plants exhibit both dominant traits (round yellow seeds: Since r is not capitalised, the possible combinations are RRYY, RRYy, RrYY, and RrYy.

• 3 plants exhibit one dominant and one recessive trait (round green seeds: Rryy, rrYY).

• 3 plants exhibit the other dominant and recessive traits (wrinkled yellow seeds: rrYy, Rryy).

• 1 plant exhibits both recessive traits (wrinkled green seeds: Of these, the four-letter phrase ‘rryy’ was extracted.

Mechanism behind Independent Assortment

The mechanism is explained below-

Meiosis and Genetic Variation:

Meiosis consists of two stages; meiosis I and meiosis II, in prophase I homologous chromosomes form pairs and undergo crossing over. This process leads to the formation of different alleles on chromosomes, thus increasing the genetic variation of the young ones.

Role of Homologous Chromosomes and Allele Behavior:

Homologous chromosomes are two chromosomes that are inherited from the first allele and two that are inherited from the second allele, both having the same genes. During meiosis, these chromosomes separate into different gametes during anaphase I, and this is why alleles for different traits are independent unless they are linked on the same chromosome.

Contribution to Genetic Diversity:

Independent assortment is also important in increasing genetic variation since it produces distinct allele combinations within offspring. This variability helps in fitness whereby organisms can change in response to different circumstances and helps in evolutionary mechanisms by enhancing the genetic pool’s flexibility.

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