Download Unit 3 - Genetics - Notes - Part 1.pps

Unit 3 - Genetics
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My most favorite unit!
Genetics – the study of how traits are passed from parent
to offspring (sometimes called heredity)
Genetic information for all organisms – stored in the base
sequences of DNA (order of A, T, C & G)
Within the eukaryotic cell, DNA is present in the nucleus
(but also present in mitochondria & chloroplasts )
DNA and protein make up chromosomes – long
condensed threads most visible when the cell is dividing
Humans cells – each contain 23 pairs of chromosomes (46
in total)
When the cell is not dividing, DNA is dispersed throughout
the nucleus as chromatin
Chromosome Structure
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chromatids – single strands of a chromosome
(contain DNA and protein)
centromere – structures that hold chromatids
together. Can be in the middle of the
chromatids, or off-center
sister chromatids – identical strands of DNA
joined together by a centromere
karyotype – chromosomes are arranged in
homologous pairs from shortest pair to longest
pair
http://learn.genetics.utah.edu/
Karyotype
Human Karyotype – p. 561 (Nelson)
Chromosome Abnormalities
Gender – Female (XX)
Edward Syndrome (trisomy 18)
Down Syndrome (trisomy 21)
Down Syndrome
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Each year in the United States, approximately one in
every 800 to 1,000 newborns has Down syndrome. This
translates to approximately 5,000 children. In the
United States today, Down syndrome affects
approximately 350,000 people. As many as 80% of
adults with this condition reach age 55, and many live
longer.
No one knows exactly why this chromosomal error
occurs, but it does appear to be related to the age of the
mother. At age 25, a woman has a one in 1,250 risk for
having a child with Down syndrome. The risk increases
to one in 952 at age 30, to one in 378 at age 35, to one
in 106 at age 40 and one in 35 at age 45. However, 80%
of children born with Down syndrome are born to
mothers under the age of 35. This is because most
babies, in general, are born to younger women.
Cloning
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Clone: a living thing genetically identical to another living
thing. Identical twins are sometimes called “nature’s
clones”.
Somatic Cell Nuclear Transfer:
 unfertilized egg has it’s nucleus removed (tiny needle)
 donor (to be cloned) individual’s somatic cell has it’s
nucleus (with DNA) removed
 Somatic cell’s DNA (even the entire cell) is then
inserted into unfertilized egg (that had it’s nucleus
removed)
 The new cell is then given a electric shock (or a certain
chemical) to get the egg to start dividing
 The egg can then be inserted into a surrogate mother
to complete development
Cloning Techniques
Types of Cloning
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Two types of Cloning:
 Reproductive Cloning: cloned embryo is allowed to
grow into a new organism. Reproductive cloning in
animals has an extremely low success rate (1-2%)
 Therapeutic Cloning: embryo is kept in a culture
and the cells grow and divide to become stem cells
(which can grow into specialized body cells).
While stem cells hold astonishing promise for
therapeutic procedures, the use of stem cells is highly
controversial because of their source, making cloning not
just a scientific issue, but a political policy issue that will
impact us all.
Human Cloning? – David Rorvik / Landrum Shettles
The Cell Cycle
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Three parts to the cell cycle:
a.
Interphase
Mitosis
Cytokinesis
b.
c.
Click here to see the cell cycle in action!
Interphase
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1.
2.
3.
3 main phases:
G1 phase (growth 1) – cell goes through basic
cell processes
S phase (synthesis) – DNA is replicated at this
stage
G2 phase (growth 2) – cell continues their
basic processes and prepares for mitosis
Mitosis tutorial
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more good websites:
http://www.biology.arizona.edu/cell_bio/tutori
als/cell_cycle/cells3.html
http://www.maxanim.com/genetics/Mitosis/M
itosis.htm
Asexual cellular division – two daughter cells
have same chromosome # as mother cell
(2n --> 2n)
Mitosis - used for growth and repair of an
multicellular organism, or for reproduction of
unicellular organisms
5 stages of the Cell Cycle
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“I P M A T”
1.
Interphase (G1, S & G2) – cell not dividing!
Prophase – chromosomes condense so you can see
2.
them
3.
Metaphase – chromosomes aligned at cell’s equator
(middle)
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Anaphase – sister chromatids start to separate to
opposite poles of cell
5.
Telophase – cell’s start to pinch off (to start
cytokinesis
Interphase
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Not considered a “phase” of mitosis.
Time when a cell is between mitotic cycles
Often called the “resting stage”
This is NOT an accurate description
Events of Interphase:
Cell is growing in size
 Proteins,organelles, and nucleic acids are
produced
 Majority of a cell’s “life”
 Prepares for mitosis
 Chromosomes and centrioles replicate.
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Relative lifetime of a cell:
1) Prophase
 The
double
chromosomes are
visible as threads
that coil and
contract into
thick rods
Events of prophase
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Centrioles migrate toward opposite ends (poles)
of the cell.
Microtubules extend from centrioles to form
asters and eventually a spindle.
Toward end of prophase chromosomes begin to
move to center (equator) of the cell
Nuclear envelope and nucleolus disappears
Late Prophase:
2) Metaphase
Centromeres line up on equator
 Two chromatids of each chromosome
become separate chromosomes
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ANIMAL
PLANT
3) anaphase
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The duplicated chromosomes move to opposite
poles
Microtubules help to move the chromosomes.
ANIMAL
PLANT
4) Telophase
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Chromosomes uncoil and get longer
Spindle fibers disappear
Nuclear membrane forms around “daughter”
nuclei.
ANIMAL
PLANT
Chromosome # in various species
Allium (Onion) cells in Mitosis
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http://www.grossmont.net/cmilgrim/Bio220/B
IO221/AlliumMitosis/mitosis_in_allium_root_t
ips.htm
Questions 1-3, page 137
-Synthesis (S)
- S, G2 and M stages
-The ratio of cell surface area to volume.
Questions 4-6, page 137
4. Students should suggest representing G0 as an offshoot of G1 because during G0, a
cell carries out normal functions but does not divide. G1 is the only stage that does
not involve DNA synthesis, duplicated DNA, or cell division.
5. The cells would probably look large and have two nuclei located at opposite sides of
the cell.
6. It is likely that the algae in the sunny pond would have a faster rate of cell division
than the algae in the shady pond. Any feasible way of testing that prediction is
acceptable. One example could be to gather algae from the two ponds and evaluate
what percentages of the sample were in each stage of the cell cycle. Presumably, a
higher percentage of the algae in the shady pond would be in G1 compared to the
algae in the shady pond.
Meiosis
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Used to cut chromosome # in half
Essential to sexual reproduction - 1/2 of DNA
(chromosomes) from each parent (sperm and
ova are called gametes)
Gametes unite in fertilization to form a zygote
In mitosis - 2n  2n (diploid  diploid)
In meiosis – 2n  n (diploid  haploid)
Meiosis - two successive nuclear divisions that
provide gametes that have half the genetic
material (1/2 the chromosomes) of the original
cell
Meiosis
2 main parts:
1. Meiosis I – cuts chromosome # in half,
homologous chromosome pairs separated
- prophase I, metaphase I, anaphase I,
telophase I
2. Meiosis II – chromatids separate (like mitosis)
- prophase II, metaphase II, anaphase II, telophase
II
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Questions 1-3, p176
1. How do homologous chromosomes differ from sister
chromatids?
 Homologous chromosomes: same genes but have
different versions of them; sister chromatids: copies of
each other, produced by DNA replication
2. Explain why an egg is so much larger than a sperm cell.
 An egg needs to provide the nutrients and building
blocks for life to begin; a sperm needs only to reach the
egg and deliver its DNA, so it is streamlined and small.
3. If, during metaphase I, all 23 maternal chromosomes
lined up on one side of the cell, would genetic diversity
increase? Explain.
 Genetic diversity would not increase because the
maternal and paternal chromosomes would not become
arranged in new combinations.
Questions 4-5
4. List the key differences between meiosis I And II.
 Meiosis I: begins with diploid cell, homologous
chromosomes separate.
 Meiosis II: begins with two haploid cells; sister chromatids
separate.
5. Both mitosis and meiosis are types of nuclear divisions, but
they result in different cell types. Describe how the steps of
meiosis I differ from mitosis.
 Mitosis: chromosomes are duplicated and the copies are
separated, one for each cell
 Meiosis I: duplicated chromosomes remain attached to each
other, each new cell gets half of each homologous pair.