Download Meiosis

How sex cells are created
Meiosis
Mitosis
Interphase 1
Interphase
Drawing
Drawing
Description
-Duplication occurs
-Chromatin DNA
-Time of cell growth
Description
-Duplication occurs
-Chromatin DNA
-Time of cell growth
Chromosome Count
4
Chromosome Count
4
Meiosis
Mitosis
Prophase1
Prophase
Drawing
Drawing
Description
-Nuclear envelope breaks down
-Chromosomes are visible
-Chromosomes pair up to form
tetrads.
-Crossing over occurs
Description
-No pairing of chromosomes
-No crossing over
Chromosome Count
Chromosome Count
8
8
Meiosis
Mitosis
Metaphase1
Metaphase
Drawing
Drawing
Description
-Tetrads line up in the middle in a
double file line.
Description
-Duplicated chromosomes line up
single file in the middle.
Chromosome Count
Chromosome Count
8
8
Meiosis
Mitosis
Anaphase 1
Anaphase
Description
- Tetrads are pulled apart such that
each side gets a duplicated
chromosome.
Description
- The duplicated chromosomes or
sister chromatids are pulled apart
into single chromosomes.
Chromosome Count
Chromosome Count
8
8
Meiosis
Mitosis
Telophase1
Telophase
Drawing
Drawing
Description
- The nuclear envelope is reforming.
Description
- The nuclear envelope is reforming.
Chromosome Count
Chromosome Count
8
8
Meiosis
Mitosis
Cytokinesis
Cytokinesis
Drawing
Drawing
Description
- Splits into two cells that are NOT
identical to each other.
Description
-Splits into two daughter cells that
ARE identical to each other.
-Mitosis is DONE!
Chromosome Count in each cell 4
Chromosome Count in each cell 4
Meiosis
Prophase 2
Drawing
Description of what is happening in each cell
-Nuclear envelope breaks down
-No pairing occurs so NO tetrads
-No crossing over occurs
Chromosome Count in each cell 4
Meiosis
Metaphase 2
Drawing
Description of each cell
-The duplicated chromosomes line up at the middle in a single file line.
Chromosome Count
4
Meiosis
Anaphase 2
Drawing
Description
- The duplicated chromosomes, or sister chromatids, are pulled apart into
individual chromosomes.
Chromosome Count of each cell 4
Meiosis
Telophase 2
Drawing
Description
- The nuclear envelope is reforming.
Chromosome Count of each cell 4
Meiosis
Cytokinesis
Drawing
Description
- Each cell splits into two non-identical cells. Now there are four cells each
with HALF the genetic information as the original parent cell.
Chromosome Count in each cell 2
Mitosis
Meiosis
Number of cells to
start the process
1
1
Number of daughter
cells at the end of the
process
2
4
How many rounds of
division does each
have
1
2
If the cell starts with
24
24 chromosomes what
will each daughter cell
have?
12
What type of cells are
these
Sex cells
Sperm and eggs
Anything non-sex
cells.
Skin, embryo, muscle,
etc.
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Mitosis is the asexual reproduction of somatic cells
(these are non-sex cells). Forms two identical
daughter cells with the same chromosome count as
the original (diploid).
Meiosis is the first stage in sexual reproduction.
Forms four genetically different cells called
gametes. Each daughter cell has ½ the DNA of the
original (haploid)
Ex: Sex Cells. Female egg formed in the ovaries.
Male sperm formed in the testes.
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Eggs (oogenesis)
◦ Although meiosis creates four haploid daughter cells
only one female cell is larger than the others. The
other three smaller polar bodies do not survive.
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Sperm (spermatogenesis)
◦ Unlike eggs there will be four usable sperm out of one
run of meiosis.
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Meiosis forms gametes which have 23
chromosomes each.
One gamete from the female (egg) and one
gamete from the male (sperm) will combine
(fertilization) to form a zygote with 46
chromosomes.
http://youtu.be/BFrVmDgh4v4
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Formation of sex/gamete cells is MEIOSIS
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Formation of body/somatic cells is MITOSIS
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The process by which an embryo forms into a
baby is MITOSIS
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The process of meiosis cuts the chromosome
count in half. Starts diploid and ends haploid.
If an organism starts with 20 chromosomes
what will their daughter cells have after a full
run of meiosis?
10 chromosomes
◦
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If an organism has 15 chromosomes in each
daughter cell how many chromosomes must it
have started with at the beginning of meiosis?

30 chromosomes
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During prophase 1 the cells form tetrads where
the duplicated chromosomes will pair up.
During this time the chromosomes can
intertwine with each other going through
crossing over. They then will exchange genetic
information.
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Due to all the different alleles that can
exchange there are 8.4 million individual
sperm or egg combinations that can result,
and when there is fertilization there is 8.4mill
x 8.4mill. = 70.6 trillion different types
of children that can occur!
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Now draw an example of crossing over!
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Fraternal: When a female ovulates two eggs
instead of one and both become fertilized.
Identical: When a female ovulates one egg
and after fertilization that one egg splits
giving both identical DNA.
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Karyotypes are a picture of a person’s
chromosomes all lined up. Images are taken
when the chromosomes are condensed and
reorganized and catagorized into 23 sets.
One of the set is from your mother and one is
from your father.
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Look at the karyotype under the normal
karyotype. What is different between them?
When there is an extra 21st chromosome also
called Trisomy 21.
The child then has 47 chromosomes instead
of 46.
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Look at the karyotype below the section
labeled turners syndrome. What is the
difference between this and the normal
karyotype?
Female only has one X chromosome where
they are now monosomy or one less
chromosome giving them 45 instead of 46.
http://turnersyndrome.org/
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Facts about turner syndrome
Turner Syndrome (TS) is a chromosomal condition that
exclusively affects girls and women. TS occurs when one
of the two X chromosomes normally found in females is
missing or incomplete. The syndrome is named after Dr.
Henry Turner, who was among the first to describe the
features in 1930s.
TS affects 1/ 2,500 live female births.
There are over 71,000 women and girls living with TS
across the United States.
It is estimated that only about 1% of fetuses with only
one X chromosome survive to term and that
approximately 10% of all miscarriages are due to Turner
syndrome.
Diagnosis of Turner syndrome is confirmed by a blood
test called a karyotype, which analyzes the chromosomal
composition of the individual.