General Biology 1
Meiosis (Reduction Division)
Each chromosome is composed of two
Meiosis sister chromatids held together by a
- It is another process of cell division. centromere and this is called dyad.
- Takes place in sexually matured organisms
(in humans this occurs at puberty stage
between ages 8 and 13 for girls and ages 9
and 14 for boys.)
- The reduction of chromosomes from diploid - Prophase I is also characterized by synapsis
to haploid. or pairing of homologous chromosomes.
Haploid Homologous chromosome
- Presence of a single set of chromosomes in - Have the same length, staining pattern,
an organism's cells. position of the centromere.
Ex. Sperm and egg cells are haploid.
Shapes of Chromosomes
Diploid
- Presence of a two set of chromosomes in an
organism's cells.
Ex. Somatic cells or body cells are diploid.
Meiosis is divided into meiosis I and meiosis II with
a short phase between them called interkinesis (aka
Interphase II).
MEIOSIS I
In a healthy person there is no presence of
Stages: telocentric chromosome. These are usually found in
- Prophase I individuals suffering from genetic disorders such as
- Metaphase I Down's syndrome.
- Anaphase I
- Telophase I & Cytokinesis One homologous chromosome comes from the
father; the other from the mother; a paired
Prophase I homologous chromosome is composed of 4
homologous chromatids or 2 homologous chromosome
is called tetrad.
Sister
Kinetochore a protein Chromatids
that is found at the
centromere and serves as
the cohesion site between
sister chromatids.
Kinetochore
- The nuclear membrane and the nucleolus Chiasma (pl., chiasmata)
start to disappears. the term used where the
- The replicated chromosomes start to crossing over takes place
condense separating the DNA from the between two non-sister
mother and the father. chromatids. From mother
- Spindle fibers became visible. From father
Homologous
Chromosomes
, Telophase I & Cytokinesis
Chiasma
- The two daughter cells will eventually
Metaphase I completely divided during telophase I.
- Nuclear membrane starts to reappear.
- Chromosomes starts to uncoil.
- As the cleavage furrow from to pinche the cell
into half it marks the ending of Meiosis I.
- Chromosomes number on both cells are the
same (1n).
- Both daughter cells are genetically different
from one another.
Interkinesis I
- The paired homologous chromosomes
(tetrads) where moved by the spindle fibers - This is a short pause between meiosis I and
towards the equator. meiosis II.
- The homologous pairs of chromosomes will - It is similar to interphase of mitosis but the
remain together. difference is there is no DNA replication of
chromosomes.
Anaphase I MEIOSIS II
Stages:
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I & Cytokinesis
Prophase II
- The homologous pairs of chromosomes
(dyads) separate and migrate towards their
respective poles.
- Sister chromatids will remain attached to their
centromere and more together towards the
poles. - The nuclear membrane disappears and DNA
starts to condense.
Meiosis (Reduction Division)
Each chromosome is composed of two
Meiosis sister chromatids held together by a
- It is another process of cell division. centromere and this is called dyad.
- Takes place in sexually matured organisms
(in humans this occurs at puberty stage
between ages 8 and 13 for girls and ages 9
and 14 for boys.)
- The reduction of chromosomes from diploid - Prophase I is also characterized by synapsis
to haploid. or pairing of homologous chromosomes.
Haploid Homologous chromosome
- Presence of a single set of chromosomes in - Have the same length, staining pattern,
an organism's cells. position of the centromere.
Ex. Sperm and egg cells are haploid.
Shapes of Chromosomes
Diploid
- Presence of a two set of chromosomes in an
organism's cells.
Ex. Somatic cells or body cells are diploid.
Meiosis is divided into meiosis I and meiosis II with
a short phase between them called interkinesis (aka
Interphase II).
MEIOSIS I
In a healthy person there is no presence of
Stages: telocentric chromosome. These are usually found in
- Prophase I individuals suffering from genetic disorders such as
- Metaphase I Down's syndrome.
- Anaphase I
- Telophase I & Cytokinesis One homologous chromosome comes from the
father; the other from the mother; a paired
Prophase I homologous chromosome is composed of 4
homologous chromatids or 2 homologous chromosome
is called tetrad.
Sister
Kinetochore a protein Chromatids
that is found at the
centromere and serves as
the cohesion site between
sister chromatids.
Kinetochore
- The nuclear membrane and the nucleolus Chiasma (pl., chiasmata)
start to disappears. the term used where the
- The replicated chromosomes start to crossing over takes place
condense separating the DNA from the between two non-sister
mother and the father. chromatids. From mother
- Spindle fibers became visible. From father
Homologous
Chromosomes
, Telophase I & Cytokinesis
Chiasma
- The two daughter cells will eventually
Metaphase I completely divided during telophase I.
- Nuclear membrane starts to reappear.
- Chromosomes starts to uncoil.
- As the cleavage furrow from to pinche the cell
into half it marks the ending of Meiosis I.
- Chromosomes number on both cells are the
same (1n).
- Both daughter cells are genetically different
from one another.
Interkinesis I
- The paired homologous chromosomes
(tetrads) where moved by the spindle fibers - This is a short pause between meiosis I and
towards the equator. meiosis II.
- The homologous pairs of chromosomes will - It is similar to interphase of mitosis but the
remain together. difference is there is no DNA replication of
chromosomes.
Anaphase I MEIOSIS II
Stages:
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I & Cytokinesis
Prophase II
- The homologous pairs of chromosomes
(dyads) separate and migrate towards their
respective poles.
- Sister chromatids will remain attached to their
centromere and more together towards the
poles. - The nuclear membrane disappears and DNA
starts to condense.
