Comparison of meiosis and mitosis

Physical Basis of Heredity 2.  Cell Division (Mitosis and Meiosis)
Significance of meiosis
Reproductive cycles
Stages of meiosis
Synaptonemal complex
Recombination nodules
Comparison of meiosis and mitosis

A comparison between meiosis and mitosis may be drawn as shown in Figure 7.16. In this connection the following similarities and differences should be noticed.

(1) While mitosis gives rise to two daughter cells, which are identical to each other as well as to the parent cell, meiosis gives rise to four daughter cells. These four cells, though resemble each other with respect to chromosome number, they differ, since paternal and maternal chromosomes would reassort during first division and would also undergo exchange of chromosome segments during crossing over. The four daughter cells will also differ from the parent cell in having half the chromosome number.
Diagrammatic representation of comparison between mitosis and meiosis.
Fig. 7.16. Diagrammatic representation of comparison between mitosis and meiosis.

(2) In meiosis, first division is reductional (separation of non-sister chromatids) and second division is equational (separation of sister Chromatids). The mitotic division is purely equational. Due to crossing over during first meiotic division, separation in first meiotic division may be partly equational also. In these regions where first division becomes equational due to crossing over, second division will now be reductional.

(3) In meiosis, homologous chromosomes undergo pairing. This pairing involves not more than two homologous chromosomes in a particular region of the chromosome, as would be evident in a autopolyploid having more than two sets of homologous chromosomes (Fig. 7.11). In mitosis, on the other hand, no chromosome pairing takes place. The only exception is giant salivary gland chromosomes, which pair throughout their lengths and may involve more than two homologous chromosomes in the same region, thus showing a distinct difference from meiotic pairing.

(4) In meiosis, with each pair of homologous chromosomes forming a bivalent, a tripartite structure called synaptonemal complex is observed under electron microscope. This structure appears at zygotene, persists in pachytene and disappears in diplotene. No such structure is observed in mitosis.

(5) In meiosis, synthesis of small fraction of DNA (0.3%) is not completed in S phase, but is delayed till zygotene. No such delayed synthesis of DNA is observed in mitosis.