Overview of Meiosis

Overview of Meiosis

Meiosis is a two-part cell division process in organisms that sexually reproduce. Meiosis produces gametes with one half the number of chromosomes as the parent cell.

In some respects, meiosis is very similar to the process of mitosis, yet it is also fundamentally different.

The two stages of meiosis are meiosis I and meiosis II. At the end of the meiotic process, four daughter cells are produced. Each of the resulting daughter cells has one half of the number of chromosomes as the parent cell.

Before a dividing cell enters meiosis, it undergoes a period of growth called interphase.

During interphase the cell increases in mass, synthesizes DNA and proteins, and duplicates its chromosomes in preparation for cell division.

Meiosis I

Meiosis I encompasses four stages:

• Prophase I
  
• Metaphase I
  
• Anaphase I
  
• Telophase I
  

In most cases, at the end of meiosis I, two daughter cells are produced.

Meiosis II

Meiosis II encompasses four stages:

• Prophase II
  
• Metaphase II
  
• Anaphase II
  
• Telophase II
  

At the end of meiosis II, four daughter cells are produced. Each of these resulting daughter cells is haploid 

Before a dividing cell enters meiosis, it undergoes a period of growth called interphase.

Interphase:

• G1 phase: The period prior to the synthesis of DNA. In this phase, the cell increases in mass in preparation for cell division. Note that the G in G1 represents gap and the 1 represents first, so the G1 phase is the first gap phase.
• S phase: The period during which DNA is synthesized. In most cells, there is a narrow window of time during which DNA is synthesized. Note that the S represents synthesis.
• G2 phase: The period after DNA synthesis has occurred but prior to the start of prophase. The cell synthesizes proteins and continues to increase in size. Note that the G in G2 represents gap and the 2 represents second, so the G2 phase is the second gap phase.
• In the latter part of interphase, the cell still has nucleoli present.
• The nucleus is bounded by a nuclear envelope and the cell's chromosomes have duplicated but are in the form of chromatin.
• In animal cells, two pair of centrioles formed from the replication of one pair are located outside of the nucleus.