What is the significance of prophase 1

Leptotene is the first of five stages of Prophase 1 and consists of the condensing of the already replicated chromosomes , this procedure continues throughout Prophase 1. The chromosomes become visible by using electron microscopy, which can distinguish between sister chromatids [3].

The appearance of the chromosomes at this stage of Prophase 1 is likened to 'a string with beads' [4] , these beads are called chromomeres. Each sister chromatid is attached to the nuclear envelope and are so close together that they can be mistaken for only one chromosome [5]. This is a very short stage of Prophase 1. Zygotene is the sub-stage where synapsis between homologous chromosomes begins. It is also known as zygonema. These synapsis can form up and down the chromosomes allowing numerous points of contact called ' synaptonemal complex ' [6] , this can be compared to a zipper structure, due to the coils of chromatin [7].

The synaptonemal complex facilitates synapsis by holding the alligned chromosomes together [8]. After the homologous pairs synapse they are either called tetrads or bivalents. Bivalent is more commonly used at an advanced level as it is a better choice due to similar names for similar states a single homolog is a 'univalent', and three homologs are a 'trivalent' [9].

A large structure called the meiotic spindle also forms from long proteins called microtubules on each side, or pole, of the cell. Between prophase I and metaphase I, the pairs of homologous chromosome form tetrads. Within the tetrad, any pair of chromatid arms can overlap and fuse in a process called crossing-over or recombination. Recombination is a process that breaks, recombines and rejoins sections of DNA to produce new combinations of genes.

In metaphase I, the homologous pairs of chromosomes align on either side of the equatorial plate. Then, in anaphase I, the spindle fibers contract and pull the homologous pairs, each with two chromatids, away from each other and toward each pole of the cell.

During telophase I, the chromosomes are enclosed in nuclei. The cell now undergoes a process called cytokinesis that divides the cytoplasm of the original cell into two daughter cells.

Each daughter cell is haploid and has only one set of chromosomes, or half the total number of chromosomes of the original cell. Meiosis II is a mitotic division of each of the haploid cells produced in meiosis I. During prophase II, the chromosomes condense, and a new set of spindle fibers forms. The chromosomes begin moving toward the equator of the cell. During metaphase II, the centromeres of the paired chromatids align along the equatorial plate in both cells. As soon as the cytoplasm divides, meiosis is complete.

There are now four daughter cells — two from each of the two cells that entered meiosis II — and each daughter cell has half the normal number of chromosomes Figure 7.

Each also contains new mixtures of genes within its chromosomes, thanks to recombination during meiosis I. Why is meiosis important? More about meiosis. Genes are packaged differently in mitosis and meiosis — but what is the effect of this difference?

What else can go wrong with chromosomes in meiosis? Meiosis is important because it ensures that all organisms produced via sexual reproduction contain the correct number of chromosomes. Meiosis also produces genetic variation by way of the process of recombination. Later, this variation is increased even further when two gametes unite during fertilization, thereby creating offspring with unique combinations of DNA.

This constant mixing of parental DNA in sexual reproduction helps fuel the incredible diversity of life on Earth. Watch this video for a summary of meiosis. Key Questions How did sexual reproduction evolve? What happens when meiosis goes wrong? Key Concepts chromosome meiosis haploid diploid recombination. Topic rooms within Genetics Close. No topic rooms are there. Browse Visually. Other Topic Rooms Genetics. Student Voices.

Creature Cast. Simply Science. Green Screen. Green Science. Bio 2. The Success Code. Why Science Matters. The Beyond. Plant ChemCast. Postcards from the Universe. Brain Metrics. Mind Read. Eyes on Environment. Accumulating Glitches. Saltwater Science. Microbe Matters. You have authorized LearnCasting of your reading list in Scitable. Do you want to LearnCast this session? This article has been posted to your Facebook page via Scitable LearnCast.

Change LearnCast Settings. Scitable Chat. Register Sign In.