1 / 56

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).

urbano
Télécharger la présentation

Cell Division

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related