Transcript Mysterious Meiosis

Mysterious Meiosis
I. Very Important Vibrant
Vocabulary
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Heredity: Transmission of traits from one
generation to the next
Variation: Offspring differ from parents
and siblings
Genetics: Scientific study of heredity and
hereditary variation
Locus: A gene’s specific location along
the length of a chromosome
III. Very Important Vibrant
Vocabulary
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Genes program cells to make proteins,
proteins produce traits
III. Very Important Vibrant
Vocabulary
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Karyotype: Organization of a cell’s
chromosomes by number, size, and type
Diploid: A cell with a full set of chromosomes
(23 pair = 46 chromosomes)
Homologous Pairs: A pair of chromosomes
(chromatids) that have the same genes, but
different forms of the genes (1 from mom, 1
from dad)
III. Very Important Vibrant
Vocabulary
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Sex Chromosomes: A special pair of
chromosomes that make us girl or boy
XX-Female
XY-Male (non-homologous)
Autosomes: The 22 other pairs of chromosomes
Tetrad: Homologous chromosomes that are
copied and stuck at the centromere.
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(Four copies of the chromosome, Two from each
parent)
III. Very Important Vibrant
Vocabulary
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Haploid (gametes): Cells with half the
chromosomes, No homologous pairs
22 autosomes + 1 sex chromosome = 23
chromosomes
Zygote: Haploid sperm and haploid egg =
Diploid zygote
IV. Meiosis...The Details
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Diploid 46 to Haploid 23
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1. Interphase I
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**DNA Replication occurs
IV. Meiosis...The Details
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2. Prophase I
Homologous pairs partner up
Synapsis...Attaches homologous
chromosomes tightly together into a
tetrad
Crossing over occurs now
Spindle fibers form, nuclear membrane
disappears
IV. Meiosis...The Details
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3. Metaphase I
Chromosomes line up on metaphase plate
in homologous pairs
IV. Meiosis...The Details
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4. Anaphase I
Sister chromatids remain attached at
centromere
Move as a unit to the poles
IV. Meiosis...The Details
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5. Telophase I and Cytokinesis
Cells split
IV. Meiosis...The Details
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6. Prophase II
Spindle forms
IV. Meiosis...The Details
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7. Metaphase II
Line up in the middle again
IV. Meiosis...The Details
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8. Anaphase II
Centromeres break and sister chromatids
(chromosomes) move to the poles
IV. Meiosis...The Details
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9. Telophase II and Cytokinesis:
Chromosomes to Chromatin
Four daughter cells are formed
Ta da!! Sex Cells!!
V. Sources of Variation in Meiosis
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A. INDEPENDENT ASSORTMENT
When chromosomes line up during
Metaphase I, they do so independently of
each other. This results in different
combinations of chromosomes in gametes
because every time they line up they do it
differently.
V. Sources of Variation in Meiosis
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B. CROSSING OVER
During Prophase I, homologous
chromosomes pair tightly and pieces of
one chromosome can cross over to the
homologous chromosome. This results in
chromosomes that have a combination of
maternal and paternal genes.
V. Sources of Variation in Meiosis
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C. RANDOM FERTILIZATION
The egg that is fertilized is one of 8 million
chromosome combos. The sperm that reaches
the egg is also one of 8 million combos. This
results in over 64 trillion combos of sperm and
egg from one set of parents (this is without
crossovers).
Be sure to look over page 242, Figure 13.8!!!
Very possible essay!!!!
VI. Gametogenesis in Humans (pg.
985-987)
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A. Oogenesis
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Production of ova, mature eggs
Occurs in the ovary.
Oogonia: Stem cells that make eggs
A. Oogenesis
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These stem cells multiply and then begin
meiosis. They stop meiosis at Prophase I.
The cells at this stage are called Primary
Oocytes. The cells remain here as follicles
until puberty.
A. Oogenesis
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Follicle-stimulating Hormone stimulates a follicle
to grow and
complete Meiosis I and to start Meiosis II.
Meiosis II stops....now the cell is called a
Secondary Oocyte.
Ovulation occurs, the cell then finishes Meiosis II
when it is penetrated by a sperm.
B. Spermatogenesis
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Production of mature sperm
Occurs in the seminiferous tubules of the
testes.
Spermatogonia: Stem cells that make
sperm
100-650 million sperm per ejaculation.
Men can ejaculate daily with no loss of
fertility capactity.
C. The difference between
Spermatogenesis and Oogenesis
1. In oogenesis meiotic divisions are
unequal (cytokinesis).
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One egg cell is created, three small polar
bodies degenerate
In spermatogenesis meiotic divisions are
equal.
Four sperm are created from each
spermatogonia
C. The difference between
Spermatogenesis and Oogenesis
2. At birth, the ovary contains all of the
primary oocytes it will ever have.
Spermatogonia go through meiosis all
through a man’s life.
3. Oogenesis has long “resting” periods.
Spermatogenesis is uninterrupted.