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Yunxi Shi

on 10 November 2013

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Transcript of meiosis

- The DNA in each individual
chromosome or chromatid replicates.
- Each chromatid now has an identical
copy attached.

1. Mitosis
Now, we will introduce the procedures of Mitosis and Meiosis respectively.

Firstly, let's talk about Mitosis.
Mitosis is the process of
dividing a cell and its nucleus
into two cells which each
have their own nucleus.It produces
two cells with the same diploid
(two sets) number of chromosomes

In general, mitosis actually
has six different phases.

Chromosome condense.
Nucleolus dissipates.
Centrioles migrate to opposite
sides of cell
spindle fiber network forms
Chromosomes line up at the
equatorial plate. The nuclear mem-
brane completely dissolve.

-Chromosomes continue to condense
Centrioles reach opposite ends.
-Spindle fibres attach to centromeres of chromosomes.
-Nuclear membrane starts to dissolve

-The copies of each chromosome
are pulled apart.
-They gather at opposite end of the cell.
-There is now an identical
set of chromosomes at each end.

-Chromosomes lengthen
-Spindle fibres dissolve
-Nuclear membrane forms
around chromosomes
-Cell begins to split.


2. Meiosis
Cells undergo a round of DNA replication,
forming duplicate chromosomes.
It is the same as Mitosis.

Prophase I:
The replicated chromosomes condense.
Homologous chromosomes come together in synapsis and crossing over occurs. Chromosomes attach to the spindle.
Metaphase I:

Chromosomes line up
at the equatorial plate.
Anaphase I:

-The homologous chromosomes of
the tetrad separate from each other
and move to different ends of the cell
-This is called DISJUNCTION
Telophase I:

The first meiotic division ends as the
cytoplasm divides into two daughter cells.
The process by which
a cell replicates its DNA,
then undergoes 2 nuclear
divisions to form haploid
sex cells.

Meiosis produces four cells
with only one set of chromosomes
(haploid). Actually, meiosis needs
to divide twice.

Prophase II
In prophase II, the centrioles in the two new cells
move to opposite poles and new spindle fibres
form. The chromosomes became attached to the
Metaphase II
The chromosomes become arranged on the equatorial plate.
Anaphase II
The centromeres separate and the sister chromatids—now individual chromosomes
—move toward the opposite poles of the cell.
Telophase II
A nuclear envelope forms around each set of chromosomes and cytokinesis occurs, producing four daughter cells, each with a haploid set of chromosomes.
Klinefelter syndrome is typically caused by
If a pair of sex chromosomes fails to separate
during the formation of an egg (or sperm), this is referred to as nondisjunction
When that egg unites with a normal sperm to form an embryo, that embryo may end up with three copies of the sex chromosomes (XXY) instead of the normal two (XY).
The extra chromosome is then copied in every cell of the baby's body

Testosterone replacement therapy (TRT)
is the best way to treat this disorder. It works by increasing a guy's testosterone levels until they are within the normal range. This can help people who get Klinefelter syndrome to develop bigger muscles, a deeper voice, growth of the penis, and facial and body hair. It also can help them improve bone density and reduce any breast growth. However, testosterone therapy cannot increase testicle size or reverse infertility.
Klinefelter Syndrome
Klinefelter syndrome or Klinefelter's syndrome, is the set of symptoms resulting from additional X genetic material in males.
Boys with Klinefelter syndrome might have the following of physical signs:

1. a taller, less muscular body than other boys their age
2. broader hips, longer legs, and weaker bones
3. a lower energy level
4. smaller penis and testicles
5. delayed puberty or only going through puberty partway (or, in rare cases, not at all)
6. may have difficulty with spelling, reading, writing, and paying attention. They may tend to be quiet, shy, and more reserved or sensitive than other guys. Some boys with Klinefelter syndrome are less interested in sports or physical activities.
What Causes It?
Klinefelter syndrome is not passed down through families like some genetic diseases. Instead, it happens randomly from an error in cell division when a parent's reproductive cells are being formed. If one of these cells is part of a successful pregnancy, a baby boy will have the XXY condition.
Mitosis & Meiosis
Full transcript