Post on 29-Dec-2015
Cell Division
Meiosis
Relationship Between Meiosis and Genetics
• Meiosis results in egg (females) and sperm (males) cells.
• When egg and sperm combine a new human is formed.
• The egg carries the genes from mom and the sperm carries the genes from dad
• You are a combination of genes from your mom and your dad!
• Your eye color, hair color etc. all depends on which egg cell and sperm cells combine!
Let Us Review Mitosis
• Cellular division involving replication and division of chromosomes (DNA).
• New cell contains complete set of chromosomes. (Two copies of genetic info.)
• Results in DIPLOID cells (chromosomes occur in pairs)
Diploid Cells
• Chromosomes after replication (ready for mitosis)
• Chromosomes in early interphase (actually chromatin)
Both are Diploid
Homologous Pairs
Diploid Cells cont.
• All body cells are diploid.
• Sex cells: egg and sperm are the only haploid cells
Sex Cells
• Germ Cells
– Also know as Sex Cells
• Only contain one copy of genetic information
• Have one chromosome of each pair or half that of diploid cells.
• Haploid (N) state.
Why is Haploid Important?
• If diploid cells are fertilized…
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Chromosome will keep doubling!!
2N + 2N 4N
Why is Haploid Important?
• If haploid cells are fertilized…
+
Like all cells of the body!!
N + N 2N
Sexual Reproduction
• Reproductive process in which haploid sex cells (gametes) fuse to produce a diploid fertilized egg (zygote)
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EGG SPERM Fertilized Egg
GAMETES
(ZYGOTE)
# of Chromosomes
Total Chromosomes
in a diploid cell
# of homologous
pairs in a diploid cell
Total chromosomes
in haploid cell
HUMAN 46CAT 36
23 23
1818
MEIOSIS
• Cell division that reduces the number of chromosomes in half
• Occurs in sex cells (germ cells: Egg and Sperm)
• Two Divisions– MEIOSIS I
– MEIOSIS II
Meiosis I
Meiosis II
Prophase I
• Chromosomes form• Nuclear membrane and
nucleolus disappear• Synapsis – homologous
chromosomes pair up• Crossing Over –
exchange of DNA creating genetic variability
Metaphase I
• Homologous chromosomes line up at the equator
Anaphase I / Telophase I
ANAPHASE I:
• Homologous chromosomes separate and move to opposite poles
• Cells are still diploid
TELOPHASE I:
• Cell membrane pinches in
Interphase????
Prophase II
• Cells are haploid.
• Cells get ready to divide again.
Metaphase II
• Chromosomes align at the equator
• Looks like mitosis
Anaphase II / Telophase II
ANAPHASE II:
• Sister chromatids move to opposite poles
TELOPHASE II:• Cell membrane pinches in
• Nuclear membrane reappears.
Resulting Sex Cells
• Four HAPLOID sex cells are produced.
MEIOSIS
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