Download Cellular Reproduction

Cellular Reproduction
MXMS 7th Grade Science
What is cell division?
•
2 primary methods allow for cells to divide and
reproduce themselves:
A. Mitosis: produces identical offspring
B. Meiosis: produces genetically diverse offspring
Mitosis
Mitosis
•
1 parent cell is able to produce 2 identical
daughter cells (diploid cells)
•
known as asexual reproduction
•
ex: it is used in humans to repair cuts & scratches
(we want identical cells for replacement!)
Mitosis
•
Phases of Mitosis:
A. Interphase
1. Growth phase #1
2. Synthesis phase
3. Growth phase #2
B. Prophase
C. Metaphase
D. Anaphase
E. Telophase
1. Ends with cytokinesis
Mitosis
•
Interphase is the longest phase (not officially mitosis)
•
Includes three events:
A. Growth phase #1—the cell grows to make room for duplication of its
organelles
B. Synthesis—the cell’s DNA strands are duplicated!
C. Growth phase #2—the cell continues to grow
Mitosis
•
Prophase:
A. Nucleus itself breaks down
B. Strands of DNA left behind (chromatin),
condense into chromosomes
Chromosomes
•
Contain the DNA of living organisms
•
Made up of two (sister) chromatids joined in the
middle (by the centromere)
Mitosis
•
Metaphase:
A. Chromosomes line up in the middle of the cell
Mitosis
•
Anaphase:
A. Chromosomes break at centromeres (middle)
B. Sister chromatids move to opposite ends of the
cell
Mitosis
•
Telophase:
A. Two new nuclei reform
B. Chromosomes unwind back into chromatin
strands
C. Cytokinesis occurs last, physically pinching the
cytoplasm in half, creating two new cells
Meiosis
Meiosis
•
1 parent cell is able to produce 4 genetically diverse daughter
cells (haploid cells)
•
known as sexual reproduction
•
divided into two parts:
A. Meiosis I is where crossover occurs & the parent cell splits
B. Meiosis II is very similar to Mitosis, where the two remaining
daughter cells are split again to produce four cells with half
the chromosomes
•
ex: it is used to produce humans (we all look different for a reason!)
•
Phases of Meiosis:
A.
Interphase
1.
Growth phase #1
2.
Synthesis phase
3.
Growth phase #2
B.
Prophase #1
C.
Metaphase #1
D.
Anaphase #1
E.
Telophase #1
F.
Prophase #2
G. Metaphase #2
H.
Anaphase #2
I.
Telophase #2
4. ends with Cytokinesis
Meiosis
Meiosis
•
Interphase is the longest phase (not officially meiosis)
•
Includes three events:
A. Growth phase #1—the cell grows to make room for duplication of its
organelles
B. Synthesis—the cell’s DNA strands are duplicated!
C. Growth phase #2—the cell continues to grow
Meiosis I
•
Prophase # 1:
A. Nucleus itself breaks down
B. Strands of DNA left behind
(chromatin), condense into
chromosomes
C. DNA is exchanged as chromosomal
crossover occurs—this leads to the
genetic diversity in each of us
Meiosis I
•
Metaphase # 1:
A. Homologous chromosomal pairs line up in the
middle of the cell
Meiosis I
•
Anaphase # 1:
A. Homologous chromosomal pairs separate and
move to opposite ends of the cell
Meiosis I
•
Telophase # 1:
A. Two new nuclei reform
B. Chromosomes unwind back into strands of
chromatin
C. Cytokinesis splits the parent cell into two new
daughter cells
What do we have?
•
Before beginning Meiosis II, let’s recap:
A. 1 parent cell has split into 2 daughter cells
B. Each daughter cell has the same # of
chromosomes as the parent cell originally
C. BUT the DNA of the chromosomes are
genetically different (due to crossover)
Meiosis II
•
(we are now dealing with 2 cells simultaneously)
•
(Interphase DID NOT occur again…what does this
mean?)
•
Prophase # 2:
A. Nuclei break down
B. Strands of DNA left behind (chromatin),
condense into chromosomes
Meiosis II
•
Metaphase # 2:
A. Chromosomes align in the middle of each cell
Meiosis II
•
Anaphase # 2:
A. Chromosomes break at centromeres (middle)
B. Sister chromatids move to opposite ends of
each cell
Meiosis II
•
Telophase # 2:
A. Four new nuclei reform (two cells splitting into
four total)
B. Chromosomes unwind back into chromatin
strands
C. Cytokinesis occurs last, physically pinching the
cytoplasm in half, creating four new cells
What do we have?
•
After Meiosis II, let’s recap:
A. 2 cells have split into 4 daughter cells
B. Each daughter cell now has half the # of chromosomes as the parent
cell originally (haploid cells)
C. AND, remember the DNA of the chromosomes are genetically different
(due to crossover in Prophase I)
D. these 4 new, genetically diverse cells are gametes (sex cells with 23
chromosomes each), also known as sperm & egg cells
E. note that the original parent cell had 46 chromosomes, so when these
gametes combine later, the new cell will have 46 chromosomes also