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6 /11/13 Living Env .

6 /11/13 Living Env . Attendance Test Information Review powerpoints Time to work on owed work. Meiosis. Division of Sex Cells. Meiosis.

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6 /11/13 Living Env .

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  1. 6/11/13 Living Env. Attendance Test Information Review powerpoints Time to work on owed work.

  2. Meiosis Division of Sex Cells

  3. Meiosis • A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. • Diploid – 2 sets of chromosomes • Haploid – 1 set of chromosomes • Homologous – chromosomes that each have a corresponding chromosome from the opposite sex parent

  4. Meiosis

  5. Meiosis Stages • Meiosis usually involves 2 distinct stages • Meiosis I • Meiosis II

  6. Prophase I • Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. • There are 4 chromosomes in a tetrad. • The pairing of homologous chromosomes is the key to understanding meiosis. • Crossing-over may occur here • Crossing-over is when chromosomes overlap and exchange portions of their chromatids.

  7. Prophase I

  8. Metaphase I • Spindle fibers attach to the chromosomes

  9. Metaphase I

  10. Anaphase I • The fibers pull the homologous chromosomes toward opposite ends of the cell.

  11. Anaphase I

  12. Telophase I & Cytokinesis • Nuclear membranes form. • The cell separates into 2 cells.

  13. Telophase I

  14. Prophase II • Meiosis I results in two haploid (N) cells. • Each cell has half the number of chromosomes as the original cell.

  15. Prophase II

  16. Metaphase II • The chromosomes line up similar to metaphase in mitosis.

  17. Metaphase II

  18. Anaphase II • Sister chromatids separate and move to opposite ends of the cell.

  19. Anaphase II

  20. Telophase II • Meiosis II results in 4 haploid cells.

  21. Telophase II

  22. Gamete Formation • In males, meiosis results in 4 sperm cells • In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction.

  23. Mitosis vs Meiosis

  24. Name That Whatzitdoing! Getting ready to divide Separating to the poles Mitosis! Now there are 2 cells! Lining up on the equator

  25. Mitosis in Onion Cells Right Before Your Eyes in the Microscope

  26. Is This Mitosis or Meiosis? Meiosis! Of course! End up with 4 cells, not 2 as in mitosis

  27. Mitosis or Meiosis?

  28. Mitosis or Meiosis?

  29. Meiosis Cell Division - Makes Gametes Humans have 46 chromosomes, so gametes have HALF that number -23 4 functional (all 4 work) sperm

  30. Meiosis Makes Ova (Eggs) Too, Of Course, But How Many are Functional? Right! Only one!

  31. Ready to Quiz Yourself?

  32. Impacts, Issues: The Color of Skin • Skin color comes from the pigment melanin • Produced by melanocytes in skin cells • More than 100 genes directly or indirectly influence amount of melanin in an individual’s skin • Lead to many variations in skin color

  33. Video: ABC News: All in the family: Mixed race twins

  34. 19.1 Basic Concepts of Heredity • Genes provide the instructions for all human traits, including physical features and how body parts function • Each person inherits a particular mix of maternal and paternal genes

  35. Basic Concepts of Heredity (1) • Genes • Humans have ~21,500 • Chemical instructions for building proteins • Locus: specific location on a chromosome • Diploid cells contain two copies of each gene on pairs of homologous chromosomes • Allele: each version of a gene

  36. A Few Basic Genetic Terms

  37. Many Genetic Traits Have Dominant and Recessive Forms

  38. Basic Concepts of Heredity (2) • Homozygous condition: identical alleles • Heterozygous condition: different alleles • Dominant allele • Effect masks recessive allele paired with it

  39. Basic Concepts of Heredity (3) • Genetic representations • Homozygous dominant (AA) • Homozygous recessive (aa) • Heterozygous (Aa) • Genotype • Inherited alleles • Phenotype • Observable functional or physical traits

  40. Genotype and Phenotype Compared

  41. DNA Structure

  42. DNA Structure • DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix. • A molecule of DNA is made up of millions of tiny subunits called Nucleotides. • Each nucleotide consists of: • Phosphate group • Pentose sugar • Nitrogenous base

  43. Nucleotides Phosphate Nitrogenous Base Pentose Sugar

  44. Nucleotides • The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”. • There are four types of nitrogenous bases.

  45. Nucleotides A T C Adenine Thymine G Guanine Cytosine

  46. Nucleotides • Each base will only bond with one other specific base. • Adenine (A) • Thymine (T) • Cytosine (C) • Guanine (G) Form a base pair. Form a base pair.

  47. DNA Structure • Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

  48. A T A A A T T T C C C G G G

  49. DNA Structure • To crack the genetic code found in DNA we need to look at the sequence of bases. • The bases are arranged in triplets called codons. A G G - C T C - A A G - T C C - T A G T C C - G A G - T T C - A G G - A T C

  50. DNA Structure • A gene is a section of DNA that codes for a protein. • Each unique gene has a unique sequence of bases. • This unique sequence of bases will code for the production of a unique protein. • It is these proteins and combination of proteins that give us a unique phenotype.

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