Transcript sexual reproduction.

Sexual Reproduction
• Sexual reproduction involves the production
of specialized cells (gametes) and the
fusion of their nuclei (fertilization )
producing a fertilized egg cell (zygote). The
zygote undergoes mitotic cell division
during its growth and maturity.
Gametogenesis
• Each body cell of an organism contains the diploid (2n) number of
chromosomes characteristic of that species. These chromosomes are
present in homologous pairs. Homologous chromosomes contain
genes for the same traits.
• Gametogenesis is the process in which gametes are produced. It
involves meiotic cell division and cell maturating. This process occurs
in specialized organs called gonads. Some organisms have only male
or female gonads while others have both, such as the earthworm and
hydra are called hermaphrodites. The result of gametogenesis is the
production of sperm (in the male) or egg cells (in the female) which
have half (n) the number of chromosomes of a normal body cell (2n).
• Monoploid = Haploid
Meiosis
• The chromosome number is reduced by
one-half and monoploid (n) nuclei which
contain one chromosome of each
homologous pair.
• Meiosis has two separate and distinct
divisions.
Meiosis
• Sexual Reproduction
only (gametes)
• Occurs in Animals &
Plants
Interphase
• Cells performing life
functions.
• Chromosomes
replicate before
division cycle begins.
Each single-stranded
chromosome results in
a pair of identical
sister chromatids.
Centrioles
Prophase I (Synapsis)
• Nuclear membrane
and Nucleolus
disappear
• Homologous Tetrads
(group of 4 chromatid
strands) synapse or
pair up
• Spindle fiber starts to
form
Metaphase I (alignment)
• Homologous Tetrads
attach to spindle fibers
and align at the
Equator
Anaphase I (disjunction)
• Homologous Tetrads
disjunct (split apart) at
their centromeres to
opposite poles
Telophase I
• Homologus
chromosomes separate
farther toward poles
• Nuclear membrane
and Nucleolus start to
reappear
Cytokinesis
• Cell membrane
pinches in and divides
the cytoplasm in
animal cells
• Cell plate forms in
plant cells to divide
cytoplasm
• Two daughter cells
formed
IPMAT-II
• Interphase II does NOT replicate the
chromosomes again. Think of it as organization.
• Prophase II, Metaphase II (centromeres replicate),
Anaphase II, and Telophase II involve the same
process as IPMAT I, however, we are dividing
Sister Chromatids.
• After the second Cytokinesis, we end up with 4
new cells, each having only half the original
chromosomes.
Meiosis Second Division
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
Cytokinesis 2
Summary
• Mitosis is associated with growth/repair and
asexual reproduction.
• Meiosis is associated with sexual reproduction.
• As a result of Mitosis cell division, the daughter
cells are identical to the original cell.
• As a result of Meiosis cell division, the resulting
cells have only one-half (n) the number of
chromosomes of the original parent cell.
Gametogenesis
• Spermatogenesis – male gonads, testes, produce
male gametes, sperm. The primary sex cell
undergoes meiosis and produces four monoploid
cells, each matures into a motile sperm cell called
the spermatozoa.
*Starts at puberty and continues for most of life thereafter
• Oogenesis – female gonad, ovary, and the gamete
is the ovum (egg). Larger than sperm, contains
stored nutrients in form of yolk. Only one
monoploid egg cell forms from meiosis and
maturation. The other cells, polar bodies,
degenerate.
*All female oogenesis done before birth
Human Gametogenesis
Continuation Of Life Video
Meiosis in Humans
Mitosis
-vsMeiosis
Animation