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MEIOSIS NOTES (11.4)
(MEIOSIS NOTES 11.4)
REPRODUCTION
• Asexual-
all of the parent
DNA goes to offspring
(miTosis-mainTains)
• Sexual -used to create
sex cells(mEiosis-rEduce)
2 TYPES OF CELLS
BODY CELLS
2) SEX CELLS
Chromosomes are:
1) autosomes
2) sex chromosomes
1)
BODY CELLS
-All
cells other than sex cells
-Also called somatic cells
-Made by mitosis
This scanning electron micrograph (courtesy of Dr. Marion J. Barnhart) shows the characteristic
biconcave shape of red blood cells.
BODY CELLS
-Contain 2 copies of each chromosome
-homologous chromosomes
-have diploid #, 2n
EX. Humans =46
SEX CELLS
-Gametes
-Eggs and sperm
-Made by meiosis
-Have haploid #, n
-EX. Humans =23
HOW DO WE GET 46 CHROMOSOMES?
Egg (haploid #) + Sperm(haploid #)
ZYGOTE (diploid #)
Ex. Humans
23 + 23 =46
MEIOSIS  SEX CELLS
mEiosis = rEduction division
-starts with 1 diploid cell and
ends up with 4 haploid cells
**Meiosis I and Meiosis II
MEIOSIS I
CROSSING OVER
Occurs during Prophase I of meiosis
*synapsis
Tetrads form and DNA is exchanged
XX
ADVANTAGE: genetic variation
CROSSING OVER
Adapted from:
Morgan T.H., Sturtevant A.H., Muller H.J., and Bridges C.B., "The Mechansim of Mendelian Heredity", 1915.
INDEPENDENT ASSORTMENT –ANAPHASE I
MEIOSIS II
Prophase II
Meiosis I results in two
haploid (N) daughter cells,
each with half the number of
chromosomes as the original.
Metaphase II
The chromosomes line up in a
similar way to the metaphase
stage of mitosis.
Anaphase II
The sister chromatids
separate and move toward
opposite ends of the cell.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
MEIOSIS DIAGRAM
EGG FORMATION
(UNEQUAL CYTOKINESIS)
AUTOSOMES VS. SEX CHROMOSOMES
COMPARING MITOSIS AND MEIOSIS
HOW MANY CELLS ARE MADE?
Mitosis
2
Meiosis
4
COMPARING MITOSIS AND MEIOSIS
ARE RESULTING CELLS GENETICALLY THE SAME
OR DIFFERENT?
MitosisGenetically the same
Meiosis Genetically different
COMPARING MITOSIS AND MEIOSIS
WHAT TYPES OF CELLS RESULT IN THE
PROCESS? (BODY CELLS OR GAMETES)
Mitosis = Body cells
Meiosis = Gametes
COMPARING MITOSIS AND MEIOSIS
WHAT ARE THE ADVANTAGES OF EACH PROCESS?
MitosisGrowth and repair
MeiosisFormation of sex cells and genetic
variation