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Intro to Meiosis

Intro to Meiosis. Meiosis I. Chromosomes appear in pairs Diploid: A cell containing a pair of each kind of chromosome. Haploid: A cell that contains half the genetic material or only one of each chromosome.

angelica-jimenez
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Intro to Meiosis

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  1. Intro to Meiosis Meiosis I

  2. Chromosomes appear in pairs • Diploid: A cell containing a pair of each kind of chromosome. • Haploid: A cell that contains half the genetic material or only one of each chromosome. • Half the genetic material is found on each chromosome. When they are paired you can find what characteristics the organism will have. • Human diploid cells have a total of 46 chromosomes. Sex cells or gametes have 23 chromosomes. • Two chromosomes that match up and are paired are called homologous chromosomes.

  3. Half of your genetic material came from your mother and half came from your father. • In order for this to be possible the body has to find a way to cut the diploid chromosomes down to half or only one of each 23 possible chromosomes types that are paired in your body. • This happens in specialized cells in your body. The specialized tissue is referred to as the gonad tissue. It is the one area that reduces our genetic make up to half in cells called gametes. This happens in the female ovary and the male testis. • This process is known as meiosis.

  4. Phases of Meiosis • Interphase: The cell replicates its chromosomes, grows, and prepares for cell division. • Prophase I: similar to normal prophase. Chromosomes coil up and spindles form. • Chromosomes pair up and form a four part structure called a tetrad consisting of two homologous chromosomes each made of two sister chromatids. • Crossing over occurs when homologous chromosomes exchange genetic material. • The estimate that during Prophase one this happens two to three times on each pair of homologous chromosomes.

  5. Crossing over illustration • Image taken from • http://biologycorner.com/bio1/meiosis.html

  6. Metaphase I • Centromere attaches to spindle fiber and tetrads line up at equator of the cell paired. Each homologous chromosome is lined up across from each other at the equator. Like football players lined up at the line of scrimmage. This is not like mitosis because the homologous chromosomes did not line up next to each other like this. See the next slide for a clearer image.

  7. Meiosis Metaphase Taken from http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0284.JPG Mitosis metaphase image taken from http://www.biologycorner.com/bio1/cellcycle.html

  8. Anaphase I • Homologous chromosomes separate from each other and move to opposite poles. (note the centromere does not split) • Image taken from • http://taggart.glg.msu.edu/bs110/meiosis4.gif

  9. Telophase I • Spindle breaks down, chromosomes uncoil, cytoplasm divides and two new daughter cells form. Each cell now has half the genetic material of the original cell. It only has one chromosome from each homologous pair however, the chromosome is still replicated so there are two copies of that chromosome in that one cell.

  10. Image taken from: http://biotech-adventure.okstate.edu/low/basics/meiosis/phases/telophase-I/telophase-I.gif

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