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Cell Division

Cell Division. Sexual Reproduction = egg & sperm OR Asexual Reproduction = single parent, no egg/sperm. Cell Division : reproduction of cells; “cells come from cells” * Basis of all life. 2 Main Roles : 1) development of fertilized egg 2) continuation of life (growth, repair).

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Cell Division

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  1. Cell Division • Sexual Reproduction = egg & sperm • OR • Asexual Reproduction = single parent, no egg/sperm • Cell Division: reproduction of cells; “cells come from cells” • * Basis of all life • 2 Main Roles: • 1) development of fertilized egg • 2) continuation of life (growth, repair)

  2. Prokaryotes = binary fission (split in half) • OR • Eukaryotes = more complex; more genetic material • chromosome: structure which contains DNA (deoxyribonucleic acid) • chromatin: long, thin fibers of DNA & protein clumping together to form chromosomes

  3. gene: specific region of DNA on chromosomes • somatic cell: all body cells except egg & sperm; contain chromosomes • (humans= 46) • Human egg & sperm (gametes) have 23 chromosomes • Prior to Cell Division… • * All chromosomes duplicate…result in 2 identical parts = sister chromatids (X-shaped) • * joined at centromere

  4. When Cells Divide • * sister chromatids separate..each goes to separate cell (daughter cell) • * each daughter cell has complete set of chromosomes • Overview of Cell Division • * eukaryotic cells divide according to cell cycle • cell cycle: sequence of events including time a cell divides until its daughter cell divide

  5. Phases in the Cell Cycle • 1) Interphase: most of cycle here • - chromosomes duplicate • - cell grows • 2) Mitotic Phase: cell division phase • Includes Mitosis & Cytokinesis • * Mitosis unique to eukaryotes • * Mitosis = continuous process but separated into defined stages

  6. Stages of Mitosis • 1) Prophase • - chromatin fibers coil to form discrete chromosomes • - sister chromatids • - nuclear membrane breaks near end • 2) Metaphase • - sister chromatids line up along center of cell

  7. Stages of Mitosis • 3) Anaphase • - sister chromatids separate & migrate to opposite ends of cell • 4) Telophase • - nuclear membrane reforms around chromosomes

  8. Cytokinesis: division of cytoplasm • - usually occurs along with telophase • - daughter cells separate

  9. Certain drugs can stop cell cycle by preventing DNA synthesis, or inhibiting synthesis of necessary proteins • Ex: cancer drugs target rapidly dividing cells – including hair follicles and digestive tracts

  10. homologous chromosome: matched pair of chromosomes; same length, genes for same traits at same loci • locus (loci = plural): specific location of a gene on a chromosome • e.g., each chromosome has gene for hair color at same loci, but the gene may be for any color of hair … impt pt = gene results in some color of hair

  11. homologous chromosomes have matching loci & • One chromosome of each pair inherited from mother & father • Human Example • Somatic cells = 46 chromosomes • 23 pairs of homologous chromosomes • 22 pairs = autosome chromosomes (F & M) • 1 pair = sex chromosomes; specific to the sex (M or F)

  12. Sex Chromosomes • Human females 1 pair (2 XX) • Human male 1 pair (1X, 1Y) • Are human male sex chromosomes homologous? • diploid cells: cells with 2 homologous sets of chromosomes in nucleus • total # chromosomes = diploid # = 2n • human diploid # = 46 (2x23=46)

  13. Humans = diploid animals because most of our cells = diploid (e.g., somatic cell) • But, eggs & sperm are not diploid • gametes: egg & sperm cells (sexual reproduction only) • haploid cells: cells with 1 homologous set of chromosomes • haploid # = n • human haploid # = 23 • Human gametes are haploid • Fertilized egg = zygote = ????

  14. Why is there so much variety among species? (e.g., diversity in humans) • Independent orientation of chromosomes • in Metaphase I --- way that tetrads line up is due to chance (random) • Results in different possible combinations of chromosomes in gametes • For humans = 8 million possible combos.!

  15. 2) Random fertilization (1 egg & 1 sperm) • What is probability that 1 of 8 million possible sperm fertilizes 1 of 8 million possible eggs???? • Humans = (8 M) * (8 M) = 64 trillion possible combinations of chromosomes due to random fertilization!

  16. 3) Crossing Over • - can result in genetic recombination • genetic recombination: producing gene combinations different from those carried by original chromosomes • * During synapsis, tetrad formed – crossing over possible • 1) homologous chromatids break at similar locations & chromatids join • 2) h. chrom. separate at Anaphase I – crossing over • 3) Meiosis II, sister chromatids separate

  17. Mendelian Genetics • genetics = science of heredity • gene: specific region of genetic material (DNA) that provides provides the cell with a “map” • Goal: determine patterns of inheritance • Mendelian Genetics • Gregor Mendel – 1860’s monk • significant findings = offspring obtain discrete heritable factors (genes) from their parents

  18. Mendelian Genetics • Gregor Mendel – 1860’s monk • -carefully chose organisms to study (garden pea), controlled pollinations, chose traits that were easy to observe, used statistical methods to analyze data • -significant findings = offspring obtain discrete heritable factors (genes) from their parents

  19. Terms • self-fertilization: plant’s egg fertilized by it’s own pollen • cross-fertilization: plant’s egg fertilized by another plant’s pollen (hybridization) • P generation: parental generation • F1 generation: filial generation; hybrid offspring of the P generation • F2 generation: offspring produced by F1 generation via self-fertilization

  20. Mendel’s Principles • 1)Principle of Segregation – pairs of genes segregate during gamete formation; fertilization pairs genes again • monohybrid cross: cross of 2 individuals that differ in 1 trait • allele: alternate form of a gene found at same loci of homologous chromosomes

  21. 1)Principle of Segregation • Ex: Flower color (P = purple, p = white) • P = 1 Purple (PP) & 1 white (pp) • F1 = all Purple (Pp) • F2 = ¾ Purple (PP & Pp) ¼ white (pp) • homozygous: identical pair of alleles • heterozygous: 2 different alleles for a trait

  22. phenotype: physical trait; appearance of organism; expressed as phenotypic ratio • genotype: genetic makeup of organism; expressed as genotypic ratio • In the flower color example….. • What is the phenotypic ratio? • What is the genotypic ratio? • ** For monohybrid cross… phenotypic ratio is always 3:1 & genotypic ratio is always 1:2:1

  23. 2)Principle of Independent Assortment • each pair of alleles segregates independently during gamete formation • dihybrid cross: cross of 2 individuals that differ in 2 traits

  24. 2)Principle of Independent Assortment • Example • P generation: Round (RR) & Yellow (YY) seeds = RRYY • Wrinkled (rr) & Green (yy) seeds = rryy • Gametes = RY and ry • F1 gen: All RrYy (Round & Yellow seeds) • Gametes = RY, Ry, rY, ry Female RY ry RrYy Male

  25. 2)Principle of Independent Assortment • Example (continued) • F2 gen: (Do Punnett Square RY Ry rY ry Female RY Ry rY ry Male

  26. 2)Principle of Independent Assortment • Example (continued) • F2 gen: (Do Punnett Square RY Ry rY ry Female RRYY RY Ry rY ry Male

  27. 2)Principle of Independent Assortment • Example (continued) • F2 gen: (Do Punnett Square RY Ry rY ry Female RRYY RY RRYy RrYY RrYy Ry rY ry Male

  28. 2)Principle of Independent Assortment • Example (continued) • F2 gen: (Do Punnett Square RY Ry rY ry Female RRYY RY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy Male

  29. Probabilities • Probability (chance) of an event occurring ranges from 0 to 1 • Probability = 0 = event will not occur • Probability = 1 = event will occur always • Tossing a Coin • What is the probability of getting a “tails”? • = 0.5 (1/2) • What is the probability of getting a “heads”? • = 0.5 (1/2) • What is the probability of getting a “heads” or a “tails”? • = P(heads) + P(tails) = 0.5 + 0.5 = 1.0

  30. Tossing 2 Coins • What is the probability of getting a “heads” on both coins? • = P(heads) x P (heads) = (0.5)*(0.5) = 0.25

  31. Flower Color Example • F1 = Pp = 0.5 P & 0.5 p gametes • F2 = Pp x Pp • 1 P (female) x 1 P (male) = 0.5 * 0.5 = 0.25 PP • 1 P (female) x 1 p (male) = 0.5 * 0.5 = 0.25 Pp • 1 p (female x 1 P (male) = 0.5 * 0.5 = 0.25 Pp • 1 p (female) x 1 p (male) = 0.5 * 0.5 = 0.25 pp • What is the probability of getting a heterozygote? • What is the probability of getting a homozygote?

  32. Why are some flowers pink? • Complete dominance = dominant & recessive alleles • Incomplete dominance = F1 offspring have phenotype somewhere between that of the 2 parents = both alleles expressed • Ex: Flower color (R = red, r = white) • P = 1 Red (RR) & 1 white (rr) • F1 = all Reddish-White = Pink (Rr) • F2 = ¼ Red (RR), ¼ white (rr), ½ pink (Rr)

  33. Incomplete Dominance

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