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Comparing Mitosis and Meiosis with reference to i. Chromosomesii. Biological significance

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Introduction

Comparing Mitosis and Meiosis with reference to i. Chromosomes ii. Biological significance Modern cell theory states that all cells are derived from other cells. This means cells must have a way of copying themselves. This is cell division; two types of cell division are Meiosis and Mitosis. The comparison will be between Meiosis 1 and Mitosis, because Meiosis 2 is much the same as Mitosis. Dividing cells have a regular pattern of events, known as the cell cycle. This cycle may be divided into two basic parts; The Interphase and the actual division (Meiosis / Mitosis). Interphase is when the cell is not dividing but duplicating its DNA and organelles. Both Meiosis 1 and Mitosis cells undergo a lot of chemical activity during this stage. The amount of DNA and organelles are doubled. Interphase is divided into three phases. The first stage is known as the growth stage, this follows cell division and is when cell organelles are synthesised. The second stage is known as the synthesis stage, this is when the DNA replicates. The finally the third stage is known as the 2nd Growth stage and this is when the centrioles replicate and energy stores increase. ...read more.

Middle

The spindle fibres are made of tubulin molecules and they shorten through the removal process. The energy for this process is provided by mitochondria, which surround the spindle fibres. Telophase In Mitosis and Meiosis Telophase the chromatids reach their respective poles and a new nuclear envelope forms around each group. The chromatids uncoil and lengthen, becoming invisible again. The spindle fibres disappear and a nucleolus forms in each new nucleus. Comparing Mitosis and Meiosis with reference to Chromosomes Mitosis Meiosis A single division of the chromosomes and the nucleus A single division of the chromosomes but a double division of the nucleus The number of chromosomes remains the same The number of chromosomes is halved Homologous chromosomes do not associate Homologous chromosomes associate to form bivalents (in prophase 1) Chiasmata aren't formed Chiasmata may be formed Crossing over doesn't occurs Crossing over does occur Daughter cells are identical to parent cells (if there are no mutations) Daughter cells are genetically different from parent cells Two daughter cells are formed Four daughter cells are formed (but in females only one is usually functional) Chromosomes shorten and widen Chromosomes coil but stay longer than in mitosis Chromosomes form a row at the equator of the spindle Chromosomes form a double row at the equator of the spindle during metaphase 1 Chromatids move to opposite poles. ...read more.

Conclusion

Each gamete contains half the number of chromosomes of the adult. It is important that meiosis, which halves the number of chromosomes in daughter cells, happens at some stage in the life cycle of a sexually reproducing organism. Therefore Meiosis is important in order for variety in organisms, and allowing them to evolve. b. The creation of genetic variety by the random distribution of chromosomes during metaphase 1 When the pairs of homologous chromosomes arrange themselves on the equator of the spindle during metaphase 1 of meiosis, they do it randomly. Even though each one of the pair determines the same general features, they're detail of the feature is different. The randomness of this distribution and independent assortment of these chromosomes produces new genetic combinations. c. The creation of genetic variety by crossing over between homologous chromosomes During prophase 1 of meiosis, equal portions of homologous chromosomes may be swapped. In this way new genetic combinations are made and linked genes separated. The variety which meiosis brings vital for to the process of evolution. By providing a varied stock of individuals it allows the natural selection of those best suited to the existing conditions and makes sure that species constantly change and adapt when these conditions change. This is the main biological significance of meiosis. Harbir Mann SFY Comparing Mitosis and Meiosis ...read more.

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