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bio week 4: team yellow - meiosis
Transcript of bio week 4: team yellow - meiosis
-Ana Juarez Stages of Meiosis -Homologous chromosomes pair with each other to form
tetrads of four chromatids and they align themselves along a single
plane in the center of the cell and this stage ends as soon
as the homologous chromosomes start being pulled away
from each other, to opposite ends of the cell. Metaphase 1 In metaphase 1, the nuclear membrane has disappeared
and the microtubules form a spindle. These spindle fibers
connect to one chromosome of each pair of homologous
chromosomes or known as the sister chromatids. Each pair of
homologues then lines up on the metaphase plate. Either
maternal or paternal homologues chromosomes may locate
towards the given pole. In anaphase, the paired chromosomes (sister chromatids)
separate and begin moving to opposite ends (poles) of the cell.
Spindle fibers not connected to chromatids lengthen and elongate
the cell. At the end of anaphase, each pole contains
a complete compilation of chromosomes. Anaphase 1 Changes that occur in a cell during anaphase:
-The paired centromeres in each distinct chromosome begin to move apart.
-Once the paired sister chromatids separate from one another, each is considered a "full" chromosome. They are referred to as daughter chromosomes.
-Through the spindle apparatus, the daughter chromosomes move to the poles at opposite ends of the cell.
-The daughter chromosomes migrate centromere first and the kinetochore fibers become shorter as the chromosomes near a pole.
-In preparation for telophase, the two cell poles also move further apart during the course of anaphase. At the end of anaphase, each pole contains a complete compilation of chromosomes. Each half has a complete haploid set of duplicated chromosomes
Composed of two sister chromatids; one or both chromatids include regions of non- sister chromatid DNA
In animal cells cleavage furrows form and in plant cells a cell plate forms
in some species, chromosomes decondense and nuclear envelopes form
Cytokinesis is the splitting of cells, creating two identical haploid daughter cells Telophase 1 Prophase 2 While chromosome duplication took place prior to meiosis I, no new chromosome replication occurs before meiosis II.
The centrioles duplicate. This occurs by separation of the two members of the pair, and then the formation of a daughter centriole perpendicular to each original centriole. The two pairs of centrioles separate into two centrosomes.
The nuclear envelope breaks down, and the spindle apparatus forms. The spindle fibers form and the chromatids line up along the Metaphase plate.
Then the nuclear membrane disappears
The homologous chromosomes attach to the microtubles at opposite poles. Metaphase 2 In order for chromatids proteins need to breakdown holding sister chromatids together at the centromere.
one separated chromosomes move individual to opposite poles
Chromosomes are dragged by spindle apparatus, their arms
are dragged along so chromosomes form v-shapes. Anaphase 2
The nuclei is now formed and chromosomes begin decondensing,
causing cytokineis occur.
One parent cell produces four daughter cells, each with a haploid
set of chromosomes which are unduplicated.
The four daugher cells are genetically distinct from one another
and from the parent cell. Telophase 2 & Cytokinesis Briefly, what meiosis does is to divide a single cell
into four cells. Each daughter cell (four) will have half the
number of chromosomes we started with. There are two
main steps - a first phase in which we divide the
number of chromosome in half. A second phase in which we
split the remaining chromosomes (this phase is
virtuallyidentical to Mitosis). Introduction to Meiosis The Importance of Meiosis Fin. Prophase 1 1. Chromosomes have already duplicated. They coil and become shorter and thicker.
2. The duplicated homologous chromosomes pair, and crossing over(the physical exchange
of chromosome parts occurs. Crossing over is the process that can give rise to genetic
recombination. At this point, each homologous chromosome pair is
visible as a bivalent (tetrad), a tight grouping of chromosomes, each
consisting of 2 sister chromatids. Sites of crossing over are
called chiasmata (singular: chaisma)
3. Nucleolus disappears.
4. Meiotic spindle, consisting of
microtubules and proteins, forms between
the two pairs of centrioles as they migrate
to opposite poles of the cell
5. Nuclear envelope disappears at the end of Prophase,
allowing the spindle to enter the nucleus.
6. Prophase is the longest phase of meiosis.
Consuming 90% of the time for the two divisions. -Meiosis makes it possible for organisms to sexually reproduce.
-Gametes are known as haploid cells and are prouced during meiosis.
-The human haploid cell (the egg and sperm) contains 23 chromosomes. & Cytokinesis