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HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?

HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?. Genes do not exist free in the nucleus of a cell; they are lined up on chromosomes. Section 10.2 Summary – pages 263-273. Diploid Cells. Section 10.2 Summary – pages 263-273.

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HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?

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  1. HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?

  2. Genes do not exist free in the nucleus of a cell; they are lined up on chromosomes. Section 10.2 Summary – pages 263-273

  3. Diploid Cells Section 10.2 Summary – pages 263-273 • In the body cells of animals and most plants, chromosomes occur in pairs. • In each pair, one you inherited from your mom, the other from your dad. From Mom From Dad

  4. Homologous Chromosomes Section 10.2 Summary – pages 263-273 The two chromosomes of a pair are called homologous chromosomes. Each pair of homologous chromosomes has genes for the same traits.

  5. Diploid Cells Section 10.2 Summary – pages 263-273 • A cell with two of each kind of chromosome is called a diploid cell.

  6. Section 10.2 Summary – pages 263-273 • Body cells (diploid) are different from sex cells. • Each person can only pass on ONE of their homologous chromosomes to their young. HUMANS = 46 CHROMOSOMES IN THEIR BODY CELLS Each parent passes 23 to their young, so that when the sperm and egg combine- it will equal 46 Chromosomes.

  7. Haploid Cells Section 10.2 Summary – pages 263-273 • So, sex cells CANNOT be diploid. • A cell containing only one of each kind of chromosome is called a haploid cell.

  8. Sexual Reproduction Section 10.2 Summary – pages 263-273 Zygote

  9. Section 10.2 Summary – pages 263-273 Diploid and Haploid Cells Chromosome Numbers of Common Organisms Organism Body Cell Sex Cell 8 Fruit fly 4 Garden pea 14 7 Corn 20 10 Tomato 24 12 26 Leopard Frog 13 17 Apple 34 Human 46 23 Chimpanzee 48 24 Dog 78 39 1260 630 Adder’s tongue fern

  10. In Humans, how many chromosomes would each of these cells have….. CHEEK CELL 46 SPERM CELL 23 EGG CELL 23 NERVE CELL 46

  11. The kind of cell division that produces sex cells (haploid) containing half the number of chromosomes as a body cell, is called meiosis. Meiosis I MeiosisII Sister chromatids separate Homologs separate Diploid Diploid Haploid

  12. Meiosis: cell division that makes SEX CELLS. Click here to see the animationhttp://www.cellsalive.com/meiosis.htm 46 It starts with a DIPLOID cell Chromosomes Replicate 92 46 46 23 23 23 23 It ends with FOUR HAPLOID cells (not identical)

  13. Section 10.2 Summary – pages 263-273 Meiosis • These haploid cells are called sex cells— gametes. • Male gametes are called sperm. • Female gametes are called eggs.

  14. Section 10.2 Summary – pages 263-273 Meiosis • When a sperm fertilizes an egg, the resulting zygote once again has the diploid number of chromosomes.

  15. Sect ion 10.2 Summary – pages 263-273

  16. Interphase Section 10.2 Summary – pages 263-273 • Growth period in which the cell replicates its chromatin (DNA).

  17. Spindle fibers Nucleus Nuclear envelope Meiosis I: Reduction Division

  18. Prophase I • Chromatin coils up. • Spindle forms. • Nuclear envelope fragments.

  19. Tetrads Form in Prophase I Homologous chromosomes(each with sister chromatids)   Join to form aTETRAD

  20. Crossing-Over in Prophase I The tetrads pair so tightly that non-sister chromatids from homologous chromosomes can actually break and exchange genetic material in a process known as crossing over.

  21. Crossing-Over Crossing over can occur at any location on a chromosome, and it can occur at several locations at the same time.

  22. Section 10.2 Summary – pages 263-273 Metaphase I • In Metaphase I, the tetrads line up in the middle, or equator. • The centromere of each chromosome becomes attached to a spindle fiber.

  23. Anaphase I Homologous chromosomes separate and move to opposite poles. Sister chromatids remain attached at their centromeres.

  24. Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two.

  25. Meiosis II: Reducing Chromosome Number The second division in meiosis is simply a mitotic division of the products of Meiosis I. Prophase II Metaphase II Telophase II Anaphase II 4 Identical haploid cells

  26. Prophase II Nuclear envelope fragments. Spindle forms.

  27. Metaphase II Chromosomes align along equator of cell.

  28. Anaphase II Equator Pole Sister chromatids separate and move to opposite poles.

  29. Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two.

  30. Results of Meiosis Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome

  31. Section 10.2 Summary – pages 263-273 Nondisjunction • The failure of homologous chromosomes to separate properly during meiosis is called nondisjunction. • This would occur in Anaphase I, when homologous chromosomes are suppose to separate from each other.

  32. Nondisjunction Section 10.2 Summary – pages 263-273 When a gamete with an extra chromosome is fertilized by a normal gamete, the zygote will have an extra chromosome. • This condition is called trisomy. • An example of this in humans is Downs Syndrome

  33. Downs Syndrome • Extra chromosome on 21 • 1 in every 1100 live births • Range from mild to severe physical and mental disabilities

  34. Nondisjunction Section 10.2 Summary – pages 263-273 • Although organisms with extra chromosomes often survive, organisms lacking one or more chromosomes usually do not. When a gamete with a missing chromosome fuses with a normal gamete during fertilization, the resulting zygote lacks a chromosome. • This condition is called monosomy. An example of this in humans is Turner’s Syndrome.

  35. Turners Syndrome • Absence of one X chromosome • Occurs in 1 out of every 2,500 live female births. • Physical characteristics • No mental disability

  36. Section 2 Check Question 1 A cell with two of each kind of chromosome is __________. A. diploid B. haploid C. biploid D. polyploid

  37. Section 2 Check Homologous Chromosome 4 The answer is A. The two chromosomes of each pair in a diploid cell are called homologous chromosomes. Each has genes for the same traits. a A Terminal Axial Inflated D d Constricted T t Short Tall

  38. Section 2 Check Question 2 Meiosis Haploid gametes (n=23) What is the importance of meiosis in sexual reproduction? Sperm Cell Meiosis Egg Cell Fertilization Diploid zygote (2n=46) Multicellular diploid adults (2n=46) Mitosis and Development

  39. Section 2 Check Meiosis is cell division that produces haploid gametes. If meiosis did not occur, each generation would have twice as many chromosomes as the preceding generation. Meiosis Haploid gametes (n=23) Sperm Cell Meiosis Egg Cell Fertilization Diploid zygote (2n=46) Multicellular diploid adults (2n=46) Mitosis and Development

  40. Section 2 Check Question 3 How does metaphase I of meiosis differ from metaphase of mitosis? (TX Obj 2; 10A)

  41. Section 2 Check During metaphase of mitosis, sister chromatids line up on the spindle's equator independent of each other. During metaphase I of meiosis, homologous chromosomes are lined up side by side as tetrads. Centromere Sister chromatids Metaphase I

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