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Chap. 20 The Role of Genes in Inheritance

Chap. 20 The Role of Genes in Inheritance. Grade 8 Science Mrs. Barr/ Mrs. Batten. Section 1: Continuing Life. Why is it important for organisms to reproduce?(30s) so they can pass on hereditary material so they can continue the species. DNA. Is a chemical

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Chap. 20 The Role of Genes in Inheritance

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  1. Chap. 20 The Role of Genes in Inheritance Grade 8 Science Mrs. Barr/ Mrs. Batten

  2. Section 1: Continuing Life • Why is it important for organisms to reproduce?(30s) so they can pass on hereditary material so they can continue the species

  3. DNA • Is a chemical • Made of 2 long strands • Each strand has a sugar, a phosphate and a nitrogen base (adenine, thymine, cytosine and guanine • Is found in cells • In chromosomes • Controls the production of proteins

  4. DNA • Is like a blueprint of a house ●stores and uses information to direct the activities of the cell & to make exact copies of itself ●Shaped like a twisted ladder

  5. How do we grow? • Mitosis is when the nucleus divides • 2 new nuclei are made

  6. Mitosis • What causes a cell to divide? • Some cell biologists have observed that size is a trigger • As a cell grows, its surface area grows slower than its volume. • The Cell Cycle • Sequence of events that occur in a cell from mitosis to mitosis • Although there are names for these steps, it is a continuous process

  7. Cell Cycle • Interphase • The largest part of the cell cycle • This time varies—ex. Yeast cell could be 2hrs, an amoeba a few days, animal in early embryo stage could be every 15-20 min. • When the cell is growing in volume • Duplicates DNA • Mitosis • Prophase • Nuclear membrane disappears • Chromosomes become visible

  8. Cell Cycle • Metaphase • Chromosomes line up in the center • Anaphase • Chromatids of each chromosome separate • Telophase • New nuclear membrane forms • Cell starts to pinch • Cytokinesis • Cytoplasm of the original cell splits

  9. Reproduction by One Organism • How does one organism reproduce? • It’s called A- sexual

  10. Reproduction by One Organism • Binary Fission • When the parent organism splits to form 2 new organisms • Budding • Happens in both unicellular and multicellular organisms • Organism develops buds on its body and when that bud reaches a certain size it separates • Regeneration • Regrowth of a missing or damaged body part

  11. Reproduction by One Organism • Cloning – organism has same DNA as parent

  12. Asexual Reproduction and Health • How come you wake up in the morning feeling fine and feel awful by the end of the day? • Bacteria reproduce through binary fission and can reproduce in as quickly as 30 minutes

  13. Reproduction by 2 Organisms • Sexual Reproduction • New organism comes from DNA of 2 cells • Sperm egg new organism

  14. How are new sex cells formed? • A body cell has 46 chromosomes (23 pairs) • A sex cell has only 23 chromosomes

  15. How do sex cells form? • Meiosis – • special kind of cell division • Two nuclear division • Produces haploid cells • Takes place only in reproductive tissues

  16. Meiosis • Meiosis has phases just like Mitosis • Meiosis I • Prophase I, Metaphase I, Anaphase I, Telophase I & Cytokinesis • Meiosis II– occurs in each of the cells produced by Meosis I, is not preceded by DNA replication • Prophase II, Metaphase II, Anaphase II, Telophase II, & Cytokinesis

  17. Sex Cells • Fertilization • The fusion of gametes (haploid cells) to form a diploid cell • This recombination allows for variation 23 23 46

  18. Diseases/Disorders • When an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy). An example of a condition caused by numerical abnormalities is Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two). Turner Syndrome is an example of monosomy, where the individual - in this case a female - is born with only one sex chromosome, an X.

  19. How about Plants? • Plants can reproduce sexually! • Female reproductive organ produces eggs (ovary ), and male produces sperm (pollen) • Some plants are either male or female • Plants rely on birds, bees, wind and water to move their egg and sperm to other plants

  20. Quick Review • How many chromosomes does a body cell have? • How many chromosomes does a sex cell have? • What is it called when sex cells are formed?

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