MITOSIS & CELL CYCLE
THE CELL CYCLE
A TYPICAL CELL GOES THROUGH
TWO DISTINCT PERIODS:
1. A PERIOD OF GROWTH
2. A PERIOD OF DIVISION
THE CELL CYCLE
THE PERIOD OF GROWTH IS
INTERPHASE:
THE PERIOD OF DIVISION IS
MITOSIS
MITOSIS IS THE DIVISION OF
SOMATIC CELLS
INTERPHASE
INTERPHASE
The longest and busiest part of a
cell’s life
3 STAGES OF INTERPHASE
1. G1-Cell growth; protein synthesis
2. S-Chromosome replication; sister
chromatids form
3. G2-Cell prepares for mitosis
A CLOSER LOOK AT MITOSIS
WHEN BODY (SOMATIC) CELLS BECOME
TOO LARGE, THEY WILL DIVIDE IN A
PROCESS KNOWN AS MITOSIS IN WHICH
TWO DAUGHTER CELLS ARE FORMED.
THERE ARE FOUR DISTINCT PHASES OF
MITOSIS:
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
PROPHASE
Prophase is the first and longest
phase of mitosis.
During prophase the long stringy
chromatin coils up into visible
chromosomes.
The duplicated chromosomes are
made up of two halves called
sister chromatids.
METAPHASE
METAPHASE: The doubled
chromosomes become attached to
the spindle fibers by their
centromeres.
The chromosomes begin to line up
on the midline of the spindle.
ANAPHASE
ANAPHASE: the
centromeres split apart
and chromatid pairs from
each chromosome
separate from each other.
TELOPHASE
TELOPHASE (final phase)
SISTER CHROMATIDS MOVE
TO OPPOSITE ENDS OF THE
CELL AND THE CYTOPLASM
BEGINS TO DIVIDE
CYTOKINESIS
CYTOKINESIS
THE PROCESS IN WHICH
THE CYTOPLASM DIVIDES
TO FORM TWO NEW CELLS
RESULTS OF MITOSIS
MITOSIS RESULTS IN TWO
GENETIC DUPLICATES OF
THE PARENT CELL.
WHY MEIOSIS?
WHEN CELLS DIVIDE BY MITOSIS, THE
NEW CELLS ARE IDENTICAL TO THE
ORIGINAL CELLS.
IF MITOSIS WAS THE ONLY FORM OF
CELL DIVISION ALL OFFSPRING
PRODUCED WOULD HAVE TWICE AS
MANY CHROMOSOMES AS ITS
PARENTS.
MEIOSIS
MEIOSIS - OCCURS IN THE
SPECIALIZED BODY CELLS
THAT PRODUCE GAMETES.
MEIOSIS CONSISTS OF TWO
SEPARATE DIVISIONS.
MEIOSIS
MEIOSIS I - BEGINS WITH ONE DIPLOID
CELL AND CREATES 2 DIPLOID CELLS.
MEIOSIS II – BEGINS WITH 2 DIPLOID
CELLS WHICH DIVIDES TO FORM 4
HAPLOID CELLS SEX CELLS.
THE HAPLOID CELLS ARE CALLED SEX
CELLS - GAMETES.
MEIOSIS
MALE GAMETES ARE CALLED SPERM.
FEMALE GAMETES ARE CALLED EGGS.
WHEN SPERM FERTILIZES AN EGG, THE
RESULTING CELL, IS CALLED A ZYGOTE.
THE FUSION OF HAPLOID SEX CELLS IS
CALLED SEXUAL REPRODUCTION.
PROPHASE I
THE CHROMATIN COILS TO FORM VISIBLE
CHROMOSOMES AND THE SPINDLES FORMS.
EACH PAIR OF HOMOLOGOUS CHROMOSOMES
COME TOGETHER TO FORM A FOUR-PART
STRUCTURE CALLED TETRAD.
CROSSING OVER
CROSSING OVER RESULTS IN NEW
COMBINATIONS OF GENES ON A
CHROMOSOME.
METAPHASE I
THE SPINDLE FIBERS PULL
THE TETRADS TO THE
EQUATOR OF THE CELL.
ANAPHASE I
ANAPHASE IS CHARACTERIZED BY
CHROMOSOMES MOVING TOWARDS
THE POLES OF THE CELL.
THE CENTROMERES HOLDING THE
SISTER CHROMATIDS TOGETHER DO
NOT SPLIT AS THEY DO IN MITOSIS.
TELOPHASE I
THE SPINDLES ARE BROKEN
DOWN, THE CHROMOSOMES
UNCOIL, AND THE CYTOPLASM
DIVIDES TO YIELD TWO NEW
CELLS.
THE SECOND DIVISION OF MEIOSIS
PROPHASE II: SPINDLE FIBERS ATTACH TO THE CHROMOSOMES.
METAPHASE II: CHROMOSOMES LINE UP RANDOMLY AT THE EQUATOR
ANAPHASE II: CENTROMERES SPLIT, SISTER CHROMATIDS SEPARATE
TELOPHASE II: THE NUCLEI RE-FORM, THE SPINDLES BREAK DOWN, THE CYTOPLASM
DIVIDES.
MITOSIS V/S MEIOSIS
MITOSIS ONLY
produces 2 identical
daughter cells
BOTH
duplication of
chromosomes occurs
MEIOSIS ONLY
produces 4 haploid cells
chromosome number is
maintained
chromosome number is
halved
daughter cells are
identical to parent
daughter cells are not
identical to parent
1 cell division is involved
2 cell divisions are involved
associated with asexual
reproduction
associated with sexual
reproduction
necessary for growth
and maintenance
produces gametes
genetic variation is a rare
occurrence
genetic variation is more
likely
THE END