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Unit 3 - Genetics My most favorite unit! My most favorite unit! Genetics – the study of how traits are passed from parent to offspring (sometimes called.

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Presentation on theme: "Unit 3 - Genetics My most favorite unit! My most favorite unit! Genetics – the study of how traits are passed from parent to offspring (sometimes called."— Presentation transcript:

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2 Unit 3 - Genetics My most favorite unit! My most favorite unit! Genetics – the study of how traits are passed from parent to offspring (sometimes called heredity) 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) 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 ) 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 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) 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 When the cell is not dividing, DNA is dispersed throughout the nucleus as chromatin

3 Chromosome Structure chromatids – single strands of a chromosome (contain DNA and protein) 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 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 sister chromatids – identical strands of DNA joined together by a centromere karyotype – chromosomes are arranged in homologous pairs from shortest pair to longest pair karyotype – chromosomes are arranged in homologous pairs from shortest pair to longest pair

4 Karyotype

5 Human Karyotype – p. 561 (Nelson)

6 Chromosome Abnormalities

7 Edward Syndrome (trisomy 18) Edward Syndrome (trisomy 18) Gender – Female (XX)

8 Down Syndrome (trisomy 21) Down Syndrome (trisomy 21)

9 Down Syndrome 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. 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. 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.

10 Cloning  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

11 Cloning Techniques

12 Types of Cloning  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%) 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). 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 Human Cloning?David Rorvik / Landrum Shettles Human Cloning?David Rorvik / Landrum Shettles

13 The Cell Cycle Three parts to the cell cycle: Three parts to the cell cycle: a. Interphase b. Mitosis c. Cytokinesis Click hereClick here to see the cell cycle in action! Click here

14 Interphase 3 main phases: 3 main phases: 1. G 1 phase (growth 1) – cell goes through basic cell processes 2. S phase (synthesis) – DNA is replicated at this stage 3. G 2 phase (growth 2) – cell continues their basic processes and prepares for mitosis

15 Mitosis tutorial Mitosis tutorial more good websites: als/cell_cycle/cells3.html more good websites: als/cell_cycle/cells3.html als/cell_cycle/cells3.html als/cell_cycle/cells3.html itosis.htm itosis.htm itosis.htm itosis.htm Asexual cellular division – two daughter cells have same chromosome # as mother cell 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 Mitosis - used for growth and repair of an multicellular organism, or for reproduction of unicellular organisms

16 5 stages of the Cell Cycle “I P M A T” “I P M A T” 1. I nterphase (G 1, S & G 2 ) – cell not dividing! 2. P rophase – chromosomes condense so you can see them 3. M etaphase – chromosomes aligned at cell’s equator (middle) 4. A naphase – sister chromatids start to separate to opposite poles of cell 5. T elophase – cell’s start to pinch off (to start cytokinesis

17 Interphase Interphase Not considered a “phase” of mitosis. Not considered a “phase” of mitosis. Time when a cell is between mitotic cycles Time when a cell is between mitotic cycles Often called the “resting stage” Often called the “resting stage” This is NOT an accurate description This is NOT an accurate description

18 Events of Interphase: Cell is growing in size Cell is growing in size Proteins,organelles, and nucleic acids are produced Proteins,organelles, and nucleic acids are produced Majority of a cell’s “life” Majority of a cell’s “life” Prepares for mitosis Prepares for mitosis Chromosomes and centrioles replicate. Chromosomes and centrioles replicate.

19 Relative lifetime of a cell:

20 1) Prophase The double chromosomes are visible as threads that coil and contract into thick rods The double chromosomes are visible as threads that coil and contract into thick rods

21 Events of prophase Centrioles migrate toward opposite ends (poles) of the cell. Centrioles migrate toward opposite ends (poles) of the cell. Microtubules extend from centrioles to form asters and eventually a spindle. 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 Toward end of prophase chromosomes begin to move to center (equator) of the cell Nuclear envelope and nucleolus disappears Nuclear envelope and nucleolus disappears

22 Late Prophase:

23 2) Metaphase Centromeres line up on equator Centromeres line up on equator Two chromatids of each chromosome become separate chromosomes Two chromatids of each chromosome become separate chromosomes ANIMAL PLANT

24 3) anaphase The duplicated chromosomes move to opposite poles The duplicated chromosomes move to opposite poles Microtubules help to move the chromosomes. Microtubules help to move the chromosomes. ANIMAL PLANT

25 4) Telophase Chromosomes uncoil and get longer Chromosomes uncoil and get longer Spindle fibers disappear Spindle fibers disappear Nuclear membrane forms around “daughter” nuclei. Nuclear membrane forms around “daughter” nuclei. ANIMAL PLANT

26 Chromosome # in various species

27 Allium (Onion) cells in Mitosis IO221/AlliumMitosis/mitosis_in_allium_root_t ips.htm IO221/AlliumMitosis/mitosis_in_allium_root_t ips.htm IO221/AlliumMitosis/mitosis_in_allium_root_t ips.htm IO221/AlliumMitosis/mitosis_in_allium_root_t ips.htm

28 Questions 1-3, page 137 -Synthesis (S) - S, G 2 and M stages -The ratio of cell surface area to volume.

29 Questions 4-6, page Students should suggest representing G 0 as an offshoot of G 1 because during G 0, a cell carries out normal functions but does not divide. G 1 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 G 1 compared to the algae in the shady pond.

30 Meiosis Used to cut chromosome # in half Used to cut chromosome # in half Essential to sexual reproduction - 1/2 of DNA (chromosomes) from each parent (sperm and ova are called gametes) 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 Gametes unite in fertilization to form a zygote In mitosis - 2n  2n (diploid  diploid) In mitosis - 2n  2n (diploid  diploid) In meiosis – 2n  n (diploid  haploid) 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 - two successive nuclear divisions that provide gametes that have half the genetic material (1/2 the chromosomes) of the original cell

31 Meiosis 2 main parts: 2 main parts: 2 main parts: 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

32 Questions 1-3, p 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 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. 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. Genetic diversity would not increase because the maternal and paternal chromosomes would not become arranged in new combinations.

33 Questions List the key differences between meiosis I And II. Meiosis I: begins with diploid cell, homologous chromosomes separate. Meiosis I: begins with diploid cell, homologous chromosomes separate. Meiosis II: begins with two haploid cells; sister chromatids 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 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. Meiosis I: duplicated chromosomes remain attached to each other, each new cell gets half of each homologous pair.


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