What is the difference between the phases of mitosis and the phases of meiosis and phases of meiosisI and phases of meiosisII

• Mitosis involves single division, resulting in the formation of two daughter cells. Meiosis involves two successive divisions, namely meiosis I and II, resulting in the formation of four daughter cells.

• Mitosis is known as equational division as the daughter cell has the same number of chromosomes as the parent cell. Meiosis I is known as reductional division where the chromosome number is reduced to half. Meiosis II is known as equational division where the sister chromatids separate while the chromosome number remains the same.

• The Mitosis prophase stage is short and does not comprise of synapsis, crossing over, and the formation of chiasmata.The meiosis Prophase 1 is the longest complex phase and divisible into five stages. They are leptotene, zygotene,pachytene, diplotene and diakinesis.

• Mitosis occurs in somatic cells and Meiosis occurs in reproductive cells.

More to know:

• Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle.
• Mitosis knows as equational division, because, eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two daughter nuclei. Mitosis is followed by cytokinesis (division of cell into two daughter cells with equal cellular components). Mitosis is divided into following four stages.

The mitotic phases are:

• Prophase: The two chromatids remain attached to centromere, the nuclear envelope break down and disappear, prophase the spindle begins to form, the centrioles separate and move apart and asters appear around them.
• Metaphase: The chromosomes congregate at an equatorial plane midway between the two ends to which the spindle tapers. The chromatids are attached to the spindle fibers at the centromeres.
• Anaphase: The two chromatids of each chromosome separate and move to opposite poles, as if pulled along the spindle fibers by the centromeres.
• Telophase: New nuclear envelopes form around the two groups of daughter chromosomes the new nucleoli begin to appear, the formation of the two daughter nuclei is completed and the spindle fibers disappear.

Cytokinesis: Separates the daughter nuclei into two new individual daughter cells.

Phases of Meiosis: I

Prophase 1: Prophase 1 of meiosis 1 is longest complex phase and divisible into five stages. They are leptotene, zygotene,pachytene, diplotene and diakinesis.

There are 2 sets of chromosomes in a diploid cell undergoing meiosis, one set contributed by the male parent and other by female parent. There are always two similar chromosomes, having same size, form and structure. They are called homologous chromosomes.

Prophase 1 is the longest complex phase and divisible into five stages. They are leptotene, zygotene,pachytene, diplotene and diakinesis

Leptotene is of very short duration and progressive condensation and coiling of chromosome fibers takes place. In Leptotene stage,

• Chromatin fibres condense and form chromosomes.
• These homologous chromosomes pair (bivalents) and form synapses. It is unique to meiosis. The bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent.
• The centromere is the part of a chromosome that links sister chromatids.
• Chromomeres aligned as beadlike granules of concentrated chromatin that constitutes a chromosome.
• During this stage both telomeres of each chromosome are attached to the same region of the nuclear envelope. Leptotene is also known as the bouquet stage because all the telomeres tend to contact the nuclear envelope in one spot so that the looped chromosomes balloon out from that point like flower petals.
• Each chromosome is attached by both of its ends to the nuclear matrix that lines the nuclear envelope with the help of a specialised structure termed the attachment plate.

The side-by-side association of homologous paternal and maternal chromosomes during the first prophase of meiosis is known as synapsis.

Crossing over occurs during pachytene. Crossing over, (recombination) involves mutual exchange of the corresponding segments of non sister chromatids.

Separation of homologous chromosomes does not take place the points called chiasmata. The chiasmata mark the sites where crossing over occurred in pachytene.

Significance of meiosis 2:

The chromososmes that separate in the anaphase of meiosis 1 are still double. Each consists of two chromatids and has 2X amount of DNA. Thus, reduction to haploidy in terms of DNA content does not occur in Meiosis 1. Truly haploid nuclei in terms of DNA content as well as chromosome number of each chromosome are separated into two different nuclei. Thus meiosis 2 is necessary.