Meiosis

Check out this great introductory video of meiosis: http://www.youtube.com/watch?v=jdQeKjEsj0U

Meiosis is a process that occurs only in sex cells like sperm and ova. This process takes place in the testes (males) and in the ovaries (females). It is comprised of two stages of cell division. The products are called gametes, which are sex cells with a haploid (n) number of chromosomes. A human sex cell undergoing meiosis will produce 4 haploid gametes with 23 chromosomes. In humans, the haploid number of chromosomes is 23 and the diploid number of chromosomes is 46. Offspring will carry genetic information from both parents instead of just a single parent.

Mitosis & Meiosis Comparison

Mitosis & Meiosis Comparison

Homologous Chromosomes

Each of the 23 chromosomes you receive from your father is matched by 23 chromosomes from your mother. Paired chromosomes similar in shape, size, gene arrangement, and gene information are called homologous chromosomes.

Homologous Chromosomes

Homologous Chromosomes

Crossing Over

During the first phase of meiosis I, prophase I, chromosomes will come together in homologous pairs and form tetrads in a process called synapsis. These are simply a pair of homologous chromosomes, each with two chromatids. As the chromosomes come together, the chromatids come into contact with each other and begin to break and exchange segments. This process is known as crossing over. This process is what gives us our genetic variability (e.g. people having different coloured eyes or hair).

Crossing Over

Crossing Over

Check out this great simulation of meiosis: http://www.youtube.com/watch?v=D1_-mQS_FZ0

Stages of Meiosis

It should be noted that there are two stages of meiosis. The first stage, meiosis I, is often referred to as the reduction division because this is where the diploid number of chromosomes is split into two haploid cells. Meiosis II is known for the separation of the two chromatids.

Meiosis I: Prophase I & Metaphase I

Meiosis I: Prophase I & Metaphase I

Meiosis I: Anaphase I & Telophase I

Meiosis I: Anaphase I & Telophase I

Meiosis II: Prophase II & Metaphase II

Meiosis II: Prophase II & Metaphase II

Meiosis II: Anaphase II & Telophase II

Meiosis II: Anaphase II & Telophase II

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