Meiosis B5

Meiosis B5

1. Meiosis

   • Gametes are produced by Meiosis
     • Meiosis involves TWO divisions. In humans it only happens in the ovaries and the testes.
       • Produces cells which have half the normal number of chromosomes
         • <--- Before the cells starts to divide, the DNA is duplicated- one arm of each chromosome is the exact copy of the other arm.
           • First Division #1: The chromosome pairs line up at the center of the cell
             • First Division #2: The pairs are then pulled apart, so each new cell has only one copy of each chromosome.
               • Second Division #1: The chromosomes line up again at the center of the cell. The arms of the chromosomes are pulled apart. Like Meiosis, membranes form around each sets of chromosomes.
                 • You get 4 gametes each with only a single set of chromosomes in it. From each side of chromosomes, new nuclei are formed. There is 4 in total
                   • After 2 gametes join at fertilisation, the zygotes grows by repeatedly dividing by MITOSIS.
   • Basic Principles
     • Gametes have half the usual number of chromosomes
       • During Sexual reproduction, the egg and the sperm combine to form a new cell called a zygote
         • All human body cells have 2 copies of the 23 chromosomes (46 total). But gametes only have one copy of each chromosome (23)
           • So when the egg and sperm combine, the zygote will contain 46 chromosomes- one set of 23 from each parent

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