Independent Assortment Of Chromosomes:What,Why,How,Causes,Types And Facts

Here, we will be covering all the aspects of the independent assortment of chromosome.

During Meiosis, it develops random combinations of chromosomes and genes on distinct homologous chromosomes. So, during Meiosis I, the homologous chromosome tetrads fall in line independently with the metaphase plate. There will be variability in gametes because of the independent assortment of chromosomes in meiosis-I.

We must first study the law of independent assortment to comprehend the independent assortment of chromosomes. The independent transportation of one diploid pair of homologous chromosomes through each gamete is defined by the independent assortment law. During Meiosis, it develops random combinations of chromosomes and genes on distinct homologous chromosomes. So, during Meiosis I, the homologous chromosome tetrads fall in line independently with the metaphase plate.

There will be variability in gametes because of the separate assortment of chromosomes in meiosis-I. Since the gametes will have distinct configurations of maternal and paternal chromosomes, the sperm and ova produced by one individual will differ from those generated by the other. The evolutionary value of sexual reproduction is that the difference in gametes produced by a single individual allows for a considerable level of variation in the genetic composition of progeny.

The process of independent assortment of chromosome

A similar pair of chromosomes are randomly assigned in the stage of anaphase I as cells divide during Meiosis, splitting and segregating independently. That is what is described as self-assortment. It leads to chromosomal configurations that are unique to each individual. Independent chromosomal layouts result from a process known as Meiosis.

Consider, for example, that after the S phase of interphase, we already have three sets of chromosomes instead of the usual 23. Consequently, there are three pairs of homologous chromosomes that we will separate and divide. The question then becomes, if this is a metaphase plate, how are these chromosome pairs going to line up? It is because, whichever way they line up, that is how they will move during anaphase-I.

There may be some crucial differences between paternal and maternal homologous chromosomes. Homologous chromosomes are identical since they share the same genes, although they may have distinct copies or alleles of the same genes. One homologous chromosome may carry the “A” version, whereas the other homologous chromosome carries the “a” version.

So, depending on which side of the line you put the “A’s” vs “a’s” on the metaphase plate, it can affect what goes into the daughter cells of meiosis-I.

When does an independent assortment of chromosomes occur?

Independent assortment of chromosomes occurs during crossing-over, which also happens during stage prophase I, the exchange of genetic material within non-sister chromatids of homologous chromosomes. During prophase I, chromosomes are aligned in pairs, mutant alleles, and extent, generating a tetrad with four chromatids.

Synapsis is the phenomenon of homologous chromosomes being paired together. While in synapsis during the meiosis phase, non-sister chromatids may divide and reconnect with their homologous partner during crossing over. Crossing over generates unique allele combinations mostly on chromosomes of haploid daughter cells. non-sister chromatids stay structurally linked at these switch locations, known as chiasmata. Allele exchange could occur if chiasmata develop between non-sister chromatids.

The types of independent assortment of chromosomes

The different types of chromosomes are categorized and grouped into three types:

1) Mutation

Independent assortment can produce 2²³, or roughly 8 million, different combinations of 23 sets of chromosomes that contain maternal and paternal homologues. It excludes significant variances caused by chromosomal mutations. Chromosome elimination, multiplication, inversion, and translation are examples of chromosomal mutations.

2) Random fertilization

Fertilization incorporates two gametes from paternal and maternal materials or alleles produced in two different individuals at random.

Furthermore, because of the random assortment and separation of chromosomes, the likelihood of pulling out the same egg or sperm cells is 1 in 8 million with random fertilization.

3) Chromatid crossing across between homologous chromosomes

When homologous chromosome pairs line up facing each other at the equator, pieces of chromatids can become twisted around each other, which happens simultaneously, as in Meiosis I. It causes the chromatids to become tense, causing pairs of chromatids to split independently.

All of the types mentioned above describe the sorting of chromosomes and multiplying them to establish genetic diversity. Furthermore, because the genes contained in the duplicated chromosomes are passed down to each subsequent cellular division, each meiotic progeny is genetically unique in the end.

The causes of independent assortment of chromosome

The causes of independent chromosome assortment result in a significant variability or heterogeneity depending on various combinations of genes that have never occurred before. In one case, genes can’t be mucked up fully at random. It occurs when two alleles are connected or on the same chromosome (homologous). 

Different inherited trait genes are present on the same chromosome and must be separated to increase recombination probability. Furthermore, the genes can exhibit different properties on different chromosomes during independent assortment.

An Independent assortment of chromosomes occurs in mitosis or Meiosis?

We know that mitosis and Meiosis are two unique methods of cell division that have quite diverse outcomes. Where mitosis begins with a diploid somatic cell and finishes with two distinct diploid daughter cells genetically identical to their parents, on the other hand, Meiosis initiates with a diploid cell. The process ends with forming four genetically different daughter cells, known as gametes.

At the cell equator, homologous chromosomes line up opposite each other in Meiosis I. Each homologous pair’s paternal and maternal chromosomes randomly fall on opposite sides of the equator. One of each homologous pair tends to end up in the daughter cell after these pairs are separated. Meiosis-I implies that each gamete is different from the other. Hence, independent chromosomal assortment occurs in Meiosis rather than mitosis.

Independent assortment of chromosomes in Meiosis

Chromosome assortment during Meiosis is one of the most important biological processes. In metaphase-I of meiosis-I, homologous chromosomes have to reorganize themselves so that, in anaphase, they can move apart.

To better comprehend the reference mentioned above, consider another example to describe this process.

So imagine each of these pairs of homologous chromosomes as a line dancing couple, and each of these couples has a coin, which they will toss to determine which side of the line to line up. Let’s assume the boy is on the left and the girl is on the right when the first couple tosses heads.

Let us suppose that the second couple tosses tails, with the boy on the right and the girl on the left. Unlike the first couple, the second one did not follow in their footsteps. It would be a dependent assortment if the boys lined up on the same side and the girls on the opposite side, depending solely on the first coin flip. It is an independent assortment, so it isn’t what this is.

As each couple does their coin flip, let’s assume the third couple tosses heads once again to determine how the lineup should go. Eventually, they end up in the daughter cells in whatever order they line up. So, while the daughter cells each have a full set of three chromosomes, they are distinct in the combination of paternal and maternal DNA or chromosomes.

As a result, we have identical starting material every time we go through Meiosis in our bodies. The possibility of having the same two daughter cells in second Meiosis, starting with the same patriarchal cell, i.e. 23 pairs of chromosomes in our situation. So, 1 in 2²³ equals 1 in approximately 8 million. As a result, 2²³= 1 in 8 million.

Where does the independent assortment of chromosomes occur?

In Meiosis, eukaryotes go through independent chromosome assortment during metaphase I. Heterogeneous chromosomes are produced in the gamete. Gametes in a diploid somatic cell contain half the amount of basic chromosomes. Gametes contain haploid cells that can reproduce sexually by fusing two haploid gametes to form a fertilized egg with the entire set of chromosomes, i.e. 23 pairs of chromosomes.

The separation of chromosomes during metaphase regarding other chromosomes forms the structural basis. The homologous chromosomes are then separated. The spindle fibres drag each set of chromosomes to the contrary ends of the cell. Furthermore, the centromeres do not segregate the chromatids.

When does the independent assortment of chromosomes occur in Meiosis?

When cells divide during Meiosis, homologous chromosomes are randomly placed during the anaphase I stage and begin to separate and segregate independently of one another using spindle fibres in a process known as independent assortment. In the end, gametes with unique chromosomal combinations are produced.

Independent assortment of chromosomes genetic variation

Let’s look at an example to comprehend better genetic variation, which involves the independent assortment of chromosomes.

My sibling has my mom’s nose and dad’s eyes, whereas I have my dad’s nose and mom’s eyes. Even though we are real siblings with the same father and mother, my sibling and I inherited nose and eye attributes (as well as all other attributes) in entirely different ways. No one would ever suspect we were real siblings if they saw us with our parents. What causes this to happen? Why don’t all siblings look alike?

For a reason, physical characteristics are expressions of our genes. Gregor Mendel, a famous geneticist, found that genes are inherited at random while studying inheritance. This approach explains the law of independent assortment.

We can’t look at how genes are inherited forward without first looking at how they’re organized. Meiosis-I is a process in which chromosomes containing genes are randomly sorted and split down the middle into gamete cells, resulting in gametes.

The chromosomes go through a process known as crossing over until they are separated. The chromosomes swap genes with one another, resulting in new chromosome configurations or variations—this aids in completing the independent assortment.

While this is being worked on by independent assortment, it is also being improved. In addition, in random fertilization, Meiosis produces even more differences in the gametes that will fuse during the fertilization process, i.e., sperm and eggs fusing. As an outcome, there is a wider range of variation seen.

Hence, unless you are twins, you have a unique appearance, and all of your inherited traits from your parents differ from your sibling. That is why we humans are all so different due to genetic differences!

Facts about the independent assortment of chromosomes

During Meiosis, the chromosomes relocate randomly to different poles, known as independent assortment. After Meiosis, a gamete will have 23 chromosomes, but independent assortment implies that each gamete will have one of many distinct chromosome combinations. Like a function, independent assortment generates unique allele combinations in which chromosomes play a key role.

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