Do “animal mitosis” micro-viewers

MEIOSIS

Sex cells are produced by the process of meiosis
Meiosis:
-one cell divides into four cells with half the parent’s chromosomes
-only sexually reproducing organisms do this, in order to make sperm or egg (gametes = sex cells)
-cells start of this division with a diploid number of chromosomes (two sets of homologous chromosomes)

Homologous Chromosomes:
-each chromosome has a matching chromosome with the same size, syndrome location and genes
-they may differ in the trait on those genes, however
e.g. -two chromosomes are same size, syndrome location, and genes for hair colour and eye colour
      -one has genes for blonde hair and blue eyes, the other has the genes for brown hair and brown eyes

Diploid # = 2n# =  46 chromosomes in humans (23 pairs)
                        =  48 chromosomes in chimps (24 pairs)
                        =    8 chromosomes in fruit flies (4 pairs)
                        =  92 chromosomes in corn (46 pairs)

-every somatic (body) cell in animals and plants has a diploid number of chromosomes
-after meiosis, gametes (sperm, egg) only have a single set of chromosomes (one of each homologous pair)
-haploid number is number of chromosomes in single set

Haploid # = 1n# = 23 chromosomes in human gametes
                         =  24 chromosomes in chimp gametes
                         =    4 chromosomes in fruit fly gametes
                         =  46 chromosomes in corn gametes

MEIOSIS (continued)

-meiosis is the production of gametes with half the normal number of chromosome
-these gametes join during fertilization to make a complete set of chromosomes in a cell

-a large variety of gametes are produced by each parent
-one way variety is increased in gametes occurs during Pro phase I, first stage in meiosis

Synapses:
-joining of homologous chromosomes (occurs in prophesy I)
-homologous chromosomes join at points to form a tetras (4 chromatics)
-DNA on the two chromosomes is randomly exchanged (recombination”/“crossing over”) at points called “chiasmata”
(eg. gene for blue and brown eyes could be exchanged between two chromatids, but all other genes remain unaltered)
-see figure 5.18, p. 134
-after crossing over occurs the chromosome pairs separate at most points (pair is called a “bivalent”)
-do long sheets on meiosis

MEIOSIS (continued)

Meiosis:
first division -one diploid cell  produces two haploid cells with chromosomes each consisting of two chromatic
second division -two haploid cells produce four haploid cells with chromosomes half the size of the original

Independent (random) Assortment:
-what one pair of homologous chromosomes does is independent of the other pairs
-this contributes to the wide variety of gametes being produced
(see p. 135, teacher will describe with coloured markers or chalk)

-the two meiotic divisions in males produce four equal sized cells

-the first meiotic division in females produces two cells of different sizes
-the large cell has most of the nutrients,cytoplasm and the smaller cell is called a “polar body”
-the second meiotic division in females results in the large cell again splitting to form a polar body and a large egg
-the first polar body may or may not divide