Meiosis I

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Transcript Meiosis I

Recall the worst cut you have ever had in
your life. Record the following info in your
notes->
•Think of how the cut happened
•Remember the healing process
•Locate the scar (if any) and make
observations
Reproduction is the biological process
by which new individual organisms are
produced from pre-existing organisms.
These pre-existing organisms are
referred to as Parents/Parent
_________ cells
These new individuals are
referred to as
OFFSPRING
_______________
Reproduction is a fundamental
feature of all known life; each
individual organism exists as the
result of reproduction.
The known methods of reproduction
are broadly grouped into two main
types: sexual and asexual.
• an individual can reproduce without
involvement with another individual
of that species.
• The division of one cell into two
daughter cells is an example of
asexual reproduction.
• Not limited to single-celled organisms
Most plants have the ability to reproduce
asexually.
• requires the involvement of two
individual’s cells, typically one of
each sex.
• Normal human reproduction is a common
example of sexual reproduction.
One parent cell
Two parents cells
Identical
________offspring
Similar
_________offspring
The process by which a cell duplicates
the chromosomes in its cell nucleus, in
order to generate two, identical,
daughter nuclei
the division causes the daughter cells (each)
to have the genetic equivalent of the parent
cell.
How does
mitosis effect
chromosome
number?
Example:
Human
chromosome
number is
46
____
Which cells in the
human body carry out
mitosis?
Examples: skin cells, hair cells,
nerve cells, etc.
These cells are called Somatic Cells
Aka body cells
The process of mitosis involves a series
of complex and highly regulated steps
The sequence of events is divided into phases
These stages are
interphase, prophase,
metaphase, anaphase
and telophase.
The end of the process and start of another is
signified by the complete division of the cell
membrane CALLED CYTOKINESIS
Looking at the phases, place them in order
of how the process of mitosis occurs.
A
CC
B
D
•When the chromosomes are
replicated/duplicated
•Periods of cell growth, to prepare
for cell division
• Each duplicated chromosome is seen as
a PAIR of sister chromatids joined by
the centromere
The spindle fibers forms between the
two pairs of centrioles as they migrate
to opposite sides of the cell.
• The nuclear envelope disappears at the
end of prophase
•The centrioles are at opposite poles of
the cell.
• The chromosomes become arranged on a
plane equidistant from the two poles.
Chromosomes line up in the middle
Anaphase begins when the duplicated
chromosomes separate, and the nowdaughter chromosomes begin moving AWAY
toward opposite poles of the cell due to the
action of the spindle.
• At the end of anaphase, a complete set of
chromosomes has assembled at each pole of
the cell.
• The chromosomes begin to uncoil and assume
the characteristics of interphase.
• A nuclear envelope reforms around each
chromosome set, the spindle disappears, and
the nucleolus reforms. Nuclear division by
mitosis is complete at this point.
•equal division of the cytoplasm,
• In animal cells, cytokinesis involves the
pinching of the cell membrane into two.
•In plant cells, cytokinesis involves the
formation of the cell plate which develops into
the cell wall
Label the phases shown (1-3)
2
1
3
•A.K.A. Gametes
•Examples: human egg and sperm cells
•Function is to fertilize
•Used to carry out sexual reproduction
23 chromosomes each
•Have _____
MEIOSIS
Created by the process of __________
•Meiosis is the type of cell division by
which gamete cells (eggs and sperm) are
produced.
•Meiosis involves a reduction in the
amount of genetic material.
•A.K.A. reduction division
To maintain normal chromosome number
once fertilization occurs
23
23
46
Meiosis consists of two successive nuclear
divisions with only one round of DNA
replication.
46
Parent cell
92
46
23
46
23
23
23
4 Daughter
cells
Meiosis I
•Interphase
•Prophase
•Metaphase
•Anaphase
•Telophase
Meiosis II
•Prophase II
•Metaphase II
•Anaphase II
•Telophase II
To reduce chromosome number
START
46
2n = ____
Called the Diploid #
END
23
n = ____
Called the Haploid #
•Animals produce gametes directly through
meiosis in organs called gonads.
•Males and females of a species that
reproduces sexually have different forms of
GAMETOGENESIS (formation of
gametes)
2 Types
•spermatogenesis (male)
•oogenesis (female)