Asexual reproduction

There are two types of reproduction – sexual reproduction and asexual reproduction.

Two parents are needed in sexual reproduction, and the offspring produced are genetically different to the parents.

Only one parent is needed in asexual reproduction, and the offspring produced are genetically identical.

Cell division

  • Cell division is a process which leads to cell multiplication.
  • Every cellular organism uses the process of Cellular Division. This is where genetically identical daughter cells are produced from parent cells. The daughter cells must be able to carry out the same functions as the parent cell.
  • Before the cell divides the nucleus of the cell divides and it follows
  • Before the cell divides the nucleus of the cell divides and it follows by the division of cytoplasm. The nucleus and particularly the chromosomes within it play an important role in the link between one generation of cells to the next generation of cells to the next chromosomes contain the chemical DNA which makes exact copy of it. During nuclear division resulting in the doubling of chromosomes.
  • There are two types of cell division, Mitosis which occurs in somatic cells and Meiosis which occurs in reproductive cells.


Cellular Division occurs for:

  1. Asexual Reproduction: Single-celled, and sometimes multicellular organisms reproduce by dividing.
  2. Growth: Cells are produced so that multicellular organisms can grow.
  3. Replacement: Any cells in multicellular organisms that have been tatty out or have been damaged need to be replaced by cellular division.

Mitosis

  • Mitosisis a process of cell division that results in two genetically identical daughter cells developing from a single parent cell.
  • These chromosomes are derived from the exact replication of the DNA from the parental chromosomes and so carry the same hereditary information in their genes.
  • In multi-cellular organisms, mitosis only occurs in somatic cells, which comprise all cells in an organism excluding germ cells.
  • It also ensures that the diploid chromosome number is maintained during cell growth.

mitosis

Meiosis

  • Meiosis is a type of cell division which only occurs within the reproductive organs.
  • Meiosis the division of agerm cell involving two fissions of the nucleus and giving rise to four gametes, or sex cells, each possessing half the number of chromosomes of the original cell.
  • Meiosis occurs during the formation of sperm and egg cells in animals, and during spore formation in plants.
  • Meiosis ensures that the gametes formed are haploid so that when two gametes fuses in sexual reproduction the diploid nature of zygote is restored.

meiosis

Following are the differences between Mitosis and Meiosis:

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Differences

Mitosis

Meiosis

1 Type of Reproduction Asexual Sexual
2 Genetically Similar Different
3 Crossing Over No, crossing over cannot occur. Yes, mixing of chromosomes can occur.
4 Number of Divisions One Two
5 Pairing of Homologs No Yes
6 Mother Cells Can be either haploid or diploid Always diploid
7 Number of Daughter Cells produced 2 diploid cells 4 haploid cells
8 Chromosome Number Remains the same. Reduced by half.
9 Chromosomes Pairing Does Not Occur Takes place during zygotene of prophase I and continue upto metaphase I.
10 Creates Makes everything other than sex cells. Sex cells only: female egg cells or male sperm cells.
11 Takes Place in Somatic Cells Germ Cells
12 Chiasmata Absent Observed during prophase I and metaphase I.
13 Spindle Fibres Disappear completely in telophase. Do not disappear completely in telophase I.
14 Nucleoli Reappear at telophase Do not reappear at telophase I.
15 Steps Prophase, Metaphase, Anaphase, Telophase. (Meiosis 1) Prophase I, Metaphase I, Anaphase I, Telophase I; (Meiosis 2) Prophase II, Metaphase II, Anaphase II and Telophase II.
16 Karyokinesis Occurs in Interphase. Occurs in Interphase I.
17 Cytokinesis Occurs in Telophase. Occurs in Telophase I and in Telophase II.
18 Centromeres Split The centromeres split during anaphase. The centromeres do not separate during anaphase I, but during anaphase II.
19 Prophase Simple Complicated
20 Prophase Duration of prophase is short, usually of few hours. Prophase is comparatively longer and may take days.
21 Synapsis No Synapsis Synapsis of Homologous chromosomes takes place during prophase.
22 Exchange of Segments Two chromatids of a chromosome do not exchange segments during prophase. Chromatids of two homologous chromosome exchange segments during crossing over.
23 Discovered by Walther Flemming Oscar Hertwig
24 Function Cellular reproduction and general growth and repair of the body. Genetic diversity through sexual reproduction.
25 Function Takes part in healing and repair. Takes part in the formation of gametes and maintenance of chromosome number.