GENERAL BIOLOGY 1 QUARTER 2
Stages of Meiosis ( Reduction Division)
One Chromosomes
Al
so known as Equation division
Cell divides on somatic cells or body cells
Significance: Centromere is the region
a. growth and development where the two sister
b. making of new body cells chromatids are held together
c. repair old and damaged cells/tissues after the replication of
Produce identical diploid cells chromosome where
kinetochore is the protein
complex on the chromosome
Chromatin = DNA + Histone where spindle fibers are
attached during cell division.
WORDS TO REMEMBER
MITOSIS- equation division
Body cells -somatic cells
MEIOSIS- reduction division
Gametes -sex cells -germ cells
In humans, each cell normally contains 23 pairs of
chromosomes, for a total of 46 chromosomes
Twenty-two of these pairs, called autosomes (somatic or
body cells) look the same in both males and females
The 23rd pair, the sex chromosomes (germ cells or gametes)
Chromatid is one of the two identical halves of a differ between males and females.
chromosome that has been replicated in preparation for cell Females have two copies of the X chromosome, while males
division. have one X and one Y chromosomes.
Homologous Chromosomes
What is Meiosis?
It is a process of cell division that takes place in sexually
mature organism.
It results in the reduction of the chromosome number from
diploid to haploid in the sex cells (sperm cell and egg cell).
It ensures the genetic continuity of species and through this
process, sexual reproduction results in genetic variety of the
members of a species.
HAPLOID vs. DIPLOID
PROPHASE 1
Chromosomes condensed
and the nuclear envelope
fragments.
SYNAPSIS
HOMOLOGOUS
CHROMOSOMES bind
firmly together along their
length, forming TETRAD.
CHIASMATA form between
non-sister chromatids.
CROSSING-OVER occurs at
the chiasmata.
Spindle fibers emerge from the centrosomes
PROMETAPHASE 1- METAPHASE 1
Homologous chromosomes
are attached to spindle
microtubules at the fused
kinetochores shared by the
PLOID vs. DIPLOID sister chromatids
It is also proceeded by interphase (G1, S, and G2) Chromosomes continue to
G1 phase- focused on cell growth condense and the nuclear
S phase- DNA replication Envelope completely
G2 phase- final preparation for meiosis disappears.
MEIOSIS I (P1, M1, A1, T1)= 2 diploid cells Homologous chromosomes
MEIOSIS 2 (P2, M2, A2, T2)= 4 haploid cells randomly assemble at
theMetaphase plate where they have been maneuvered
GENE vs. ALLELE into place by the microtubules
RANDOM OR INDEPENDENT ASSORTMENT
ANAPHASE 1
Spindle microtubules pull the
homologous chromosomes
apart.
The sister chromatids are still
attached at the centromere
TELOPHASE 1
A gene is a portion of DNA that determines a certain trait.
An allele is a specific form of a gene. ... Chromosomes(consisting
of sister chromatids)
IMPORTANT EVENTS DURING PROPHASE 1 arrive at the poles of the
cell and begin to
Synapsis- tight pairing of homologous chromosomes decondense.
Tetrad-results when chromosomes line up together A nuclear envelope forms
Chiasma- forms by cross-over recombination around each nucleus and
Crossing-over- exchange of genetic materials the cytoplasm is divided
by a CLEAVAGE FURROW.
The result is 2 DIPLOID
CELLS.
CYTOKINESIS 1 ANAPHASE 2
Sister chromatids are
pulled apart by the
shortening of The
Kinetochore
microtubules.
Non-kinetochore
microtubules
lengthen the cell.
TELOPHASE 2
Chromosomes
arrive at the poles
of the cell and
decondense.
Nuclear envelopes
surround the four
nuclei.
CLEAVAGE
FURROWS divide
MEIOSIS 2 the two cells into
FOUR HAPLOID
CELLS.
During meiosis II, the sister chromatids within the two
daughter cells separate, forming four new haploid gametes.
The mechanics of meiosis II is similar to mitosis, except that CYTOKINESIS 2
each dividing cell has only one set of homologous
chromosomes.
PROPHASE 2
Chromosome
condensed.
A new spindle
begins to form.
The nuclear
envelops starts to
fragment
OVERVIEW OF MEIOSIS 2
PROMETAPHASE 2-METAPHASE 2
The nuclear
envelope disappears
as the spindle fibers
engage the
individual
kinetochores on the
sister chromatids.
Chromosomes line
up at the
metaphase plate
Errors in Mitosis and Meiosis
Mitosis
The process by which cells make exact copies of
themeselves.
One cell become two cell which grow to the same size as
the original cell making the organism grow.
Many single-celled organisms reproduce in this way.
Multicellular organisms use mitosis to grow and repair or
replace damaged worn out cells.
Errors in Mitosis
Edward’s syndrome (trisonomy 18)
Almost every organ system
affected,
1:10,000 live births.
Children with full Trisomy
18 generally do not live m
ore tha a few months
Generally due to non-disjunction (or failure to separate) of
Turner’s syndrome 45, (x0) females (trisonomy 18)
chromosomes or sister chromatids and may result to
chromosomal mutation. A condition that affects only females, results when one of
Mosaicism-is a consequence of mitosis passing on the the X chromosomes is missing or partially missing.
mutation to some cells.
*Hemophilia- a blood-clotting disorder
* Marfan’s syndrome- unusually long limbs
*Cancer
Due to non-disjunction of homologous chromosomes during Klinefelter’s syndrome 47, XXY males
Meiosis I or II results to a sperm/egg cell that lacks one
chromosome or has an extra no. of chromosome. Male sex organs; unusually small testes, sterile.
Have 1 copy = monosomy = 45 chromosomes Breast enlargement and other
Have 3 copies = trisomy = 47 chromosomes feminine body characteristics.
Normal intelligence.
Down Syndrome/Trisomy 21/ Mongolism
Patau syndrome (trisonomy 13)
Serious eye, brain, circulatory defects as well as cleft palate.
1:5000 live births. Children rarely live more than a few
months.
