Significance of Meiosis: Definition & Features

Meiosis is one of the fundamental processes that occur in all sexually reproducing organisms. The word ‘Meiosis’ was coined by J.B.Farmer and Moore in 1905. It is a special form of cell division that occurs in the gametes (gametic meiosis) or in the zygote after fertilization (zygotic meiosis). 

There are other aspects of meiosis that helps each individual to maintain their uniqueness and structural diversity, the ability to carry out vital life processes, and be able to better adapt to the various changes in the environment.

Read More: Mitosis & Meiosis

Key Terms: Cell Division, Meiosis, Mitosis, Gametes, Chromosomes, Genetics, Chromosome Number, Mutation

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What is Meiosis?

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Meiosis leads to the reduction in the number of chromosomes in the resulting cell via two series of cell division. A mature diploid sporophytic cell undergoes meiosis to give four haploid cells. In short, it is through meiosis that nature maintains the number of chromosomes in sexually reproducing organisms generation after generation. Hence, it is of utmost importance for those organisms in which the union of gametes takes place during sexual reproduction.

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Features of Meiosis

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Some of the important characteristic features of meiosis are:

• This process usually occurs during gametogenesis or sporogenesis.
• In this process, the diploid mother cell produces four haploid daughter cells.
• Chromosome number of mother cells is halved in daughter cells.
• In this process, the mother cell divides in two stages-meiosis-I and meiosis-II. 
• In meiosis-I, the chromosome number of the mother cell is halved, therefore it is called Reduction division.
• In meiosis-II, the chromosome number of the mother cell remains the same in the daughter cell, therefore this is called Equational division.
• In this process, chromosomes divide once but the nucleus and cytoplasm divide twice.
• Due to the occurrence of crossing-over, gametes produced in the process bear both paternal and maternal characteristics.

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Significance of Meiosis

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Meiosis is important because of the following:

Formation of Gametes

• In sexually reproducing haploid organisms, the gametes are formed by the process of Mitosis.
• But in diploid organisms the gametes are always formed by the process of meiosis.
• Meiosis is the prerequisite requirement to form haploid gametes in diploid organisms as it reduces the number of chromosomes to half.

Genetic Information

• It switches on the genetic information for the development of gametes or gametophytes and switches off the sporophytic information. 
• In other words, gametes with a unique genetic constitution are formed which retain their individual information in the zygote. 
• On the other hand, the sporophytic cells lose their genetic identity and get transformed into gametes, which are different from the sporophytic cells.
• Thus, the sporophytic information is switched off and gametic information is switched on.

Maintenance of Constant Chromosome Number

• Since fertilization is the union of the gametes, hence it always lead to the doubling up of the chromosomes in the zygote.
• Here meiosis plays an important role in reducing the number of chromosomes to half so that on fertilization the original number of chromosomes is restored.
• The progeny now has the same number of chromosomes as that of its parents.

Evidence of Basic Relationships

• The biochemical, physiological and cytological aspects of meiosis are almost similar in all the sexually reproducing organisms showing their basic similarity and relationship.
• Closely related organisms show a greater resemblance in the process of meiosis than with distant ones.

Assortment of Chromosomes

• Meiosis causes the segregation and independent assortment of the maternal and paternal chromosomes in the resulting gametes. 
• This happens in a random manner and each has an equal chance of receiving either of the two sets of chromosomes.

Crossing Over

• Crossing over occurs in the diplotene stage of meiosis I.
• It is the random independent recombination of hereditary units of different chromosome zones that result in the formation of new genetic combinations in the gametes.
• This ultimately leads to the introduction of variations in the offspring. 
• Moreover, crossing over occurs in every cell division and is essential for introducing variations in the progeny.

Mutations

• Chromosomal and genetic mutations can take place by irregularities of meiotic division.
• Some of these mutations are useful to the organism and are perpetuated by natural selection. 
• On the other hand, many mutations are harmful and lead to abnormalities, defective development or genetic disorders in the offspring.

Chromosomal Aberration

• The structural changes in the chromosome occurs.
• This results in a change number of genes or changed sequences of genes in the chromosomes.
• Inversion and translocation occur due to unequal crossing over between the two chromatids of non-homologous chromosomes.
• The aneuploids arise due to the non-disjunction of homologous chromosomes of a particular pair during meiosis.

Evolution

• There are many theories that suggest the importance of meiosis in the formation of new species and the evolution of the existing ones. 
• The reshuffling of genes occurs through crossing over as well as the change in the number of pairs of the chromosomes.
• This leads to the creation of new species, essentiality, and evidence of evolution.

Read More: Haploid Vs Diploid

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Things to Remember

• Meiosis is a reduction division leading to a reduction in the number of chromosomes.
• Meiosis is of two types- Gametic meiosis and zygotic meiosis.
• In Gametic Meiosis, division occurs during gamete formation and it is common in sexually reproducing diploid organisms.
• In Zygotic meiosis, the division takes place in the zygote after fertilization and it is common in sexually reproducing haploid organisms.
• The process of meiosis has two phases- reduction division and equational division.
• Meiosis helps in gamete formation and transferring maternal and paternal genes to the gametes as these are assorted independently.
• Meiosis offers to introduce variations by means of crossing over leading to a large variety of individuals in a population.
• Meiosis helps in assigning relationships among organisms of different groups.
• By means of chromosomal modification, which can be introduced during meiosis, the formation of new species and modifications of existing ones happen.
• A large number of genetic disorders in the human population is a result of errors happening during the process of meiosis.

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Previous Year Questions

1. The stage of meiosis in which pairing of homologous chromosomes starts, is called? [UPSEE 2016]
2. The exchange of segments of non-sister chromatids between homologous pair is? [DUET 2010]
3. Which of the following stages is the longest in animals? [ JIPMER 1996]
4. During meiosis -I, the number of chromosomes is? [JKCET 2015]
5. The largest phase of meiosis-I is? [WBJEE-2011]
6. In meiosis, synapsis occurs during?
7. In which stage of meiosis crossing over takes place?
8. Synapsis occurs in ...... phase of meiosis? [BCECE 2004]
9. Meiosis can be best studied in [CUCET 2011]
10. During _________stage of meiosis I, crossing over take place. [COMEDK UGET 2007]
11. Meiosis results in 
12. At which stage of meiosis does the genetic constitution of gametes is finally decided?
13. During anaphase I of meiosis
14. During pachytene stage of meiosis, the chromosomes appear
15. Identify the wrong statement about meiosis.