Difference Between Random Orientation and Independent Assortment

The key difference between random orientation and independent assortment is that random orientation is the random line up of homologous chromosome pairs at the equator during the metaphase of meiosis 1 while independent assortment refers to the inheritance of genes independently from the inheritance of any other gene.

Cell divisions make new vegetative cells or sex cells (gametes). Mitosis results in genetically identical cells while meiosis results in gametes which are genetically different. During the metaphase of meiosis, homologous chromosome pairs (one from mother and the other from father) line up at the equator as bivalents. The orientation of each pair of homologous chromosomes is random. It is not affected by the orientation of any other homologous pair. This is known as the random orientation. As a result of random orientation, chromosomes separate from each other independently during the anaphase. Because of that, alleles on the chromosomes also separate independently. Therefore, the separation of alleles on chromosomes independently from any allele on another chromosome is known as independent assortment.

CONTENTS

1. Overview and Key Difference
2. What is Random Orientation 
3. What is Independent Assortment
4. Similarities Between Random Orientation and Independent Assortment
5. Side by Side Comparison – Random Orientation vs Independent Assortment in Tabular Form
6. Summary

What is Random Orientation?

A homologous chromosome pair comprises of one maternal and one paternal chromosome. These pairs are the same size, shape and carry the same genes, but they are not genetically identical. During the metaphase of meiosis 1, homologous pairs line up at the equator. This lineup process occurs randomly. The orientation of the homologous chromosome pair is totally independent and not affected by the orientation of any homologous chromosome pair. Therefore, it is known as the random orientation. There are two possible random orientations of homologous chromosome pairs at the equator.

During the lineup process, homologous chromosomes form a tight pairing called synapsis. In synapsis, the genes on the chromatids of the homologous chromosomes are aligned with each other, facilitating and supporting the crossing over and genetic recombination. Hence, the random orientation of homologous chromosomes is another mechanism that introduces variation into the gametes or spores.

What is Independent Assortment?

The law of independent assortment is one of the three laws of Gregor Mendel. It describes how alleles or genes separate independently from one another during gamete formation. In simple words, the independent assortment is the inheritance of genes independently from the inheritance of any other gene.

A gamete receives an allele without the influence of any other allele. Therefore, the alleles are passed from parent to offspring independently. Independent assortment is totally due to the random orientation of homologous chromosomes. If the genes are completely linked, those alleles do not display independent assortment.  They tend to be inherited together as a unit.

What are the Similarities Between Random Orientation and Independent Assortment?

• Independent assortment is due to the random orientation of pairs of homologous chromosomes in meiosis I.
• Both events are extremely important in the formation of genetically different gametes.
• As a result of both events, gametes receive a unique combination of chromosomes and a unique composition of genes.
• Genetic variation within the offspring is due to these events occurring in the meiosis.

What is the Difference Between Random Orientation and Independent Assortment?

Random orientation is the random line up of homologous chromosome pairs at the cell equator while the independent assortment is the inheritance of genes independently from the inheritance of any other gene. So, this is the key difference between random orientation and independent assortment.

The below infographic summarizes the differences between random orientation and independent assortment.

Summary – Random Orientation vs Independent Assortment

Meiosis leads to the formation of genetically unique gametes. This occurs due to the random orientation of homologous chromosome pairs and independent assortment of genes/alleles. The homologous chromosome pairs line up at the metaphase plate randomly. As a result, chromosomes separate independently from one another. When chromosomes separate independently, alleles or genes on the chromosomes separate or are inherited to gametes independently. This is the process of independent assortment. Thus, this is the summary of the difference between random orientation and independent assortment. Both these events lead to the unique composition of alleles or genes in the gametes at the end of the meiosis.

Reference:

1. “7.6: Genetic Variation.” Biology LibreTexts, Libretexts, 28 Oct. 2020, Available here.
2. “The Law of Independent Assortment (Article).” Khan Academy, Khan Academy, Available here.

Image Courtesy:

1. “0330 Homologous Pair of Chromosomes” By OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “Independent assortment” By Mtian20 – Own work (CC BY-SA 4.0) via Commons Wikimedia