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Cell Reproduction.

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Presentation on theme: "Cell Reproduction."— Presentation transcript:

1 Cell Reproduction

2 Stem Cell Shakes In The News

3 Dividing Nuclear Material
Cells must accurately separate genetic material during cell reproduction Methods Mitosis Meiosis

4 Mitosis Produces two cells identical to original cell
Each cell has full DNA complement Used for growth and repair of somatic (body) cells

5 Meiosis Produces 4 cells that are not identical to parent cell
Daughter cells have half genetic complement Produces gametes (sex cells)


7 Animal Life Cycle Egg = female gamete Sperm = male gamete Zygote
Fusion of egg & sperm Full complement of genetic material

8 Diploid Cells (2N) Full genetic complement
23 pair of chromosomes in humans

9 Haploid Cells (N) Produced during meiosis
Contain only one set of chromosomes Reduction of chromosomes allows for combination to form diploid zygote

10 Fertilization One sex cell from each parent joins
Creates diploid zygote Process is called sexual reproduction

11 Animal Life Cycles Diploid phase dominates Gametes live hours to days

12 Plant Life Cycles Most have multicellular haploid phase Phase names
Gametophyte = haploid Sporophyte = diploid Either phase can dominate, depending on plant type


14 Single Cell Eukaryote Reproduction
Reproduce by mitosis Called asexual reproduction Produced two identical organisms

15 Asexual Reproduction All single cell eukaryotes Some plants
Some animals


17 Cell Cycle (Life Cycle)

18 Interphase Most of cell cycle Cell grows Organelles replicated
DNA replicated Readies for mitosis Condenses DNA

19 G1 Interphase Cell growth-doubles in size
Carries out its normal life functions

20 S Interphase DNA replicated At the end of this phase, the cell
will contain two identical copies of heredity info.

21 G2 Interphase DNA condenses into chromosomes
Strands = sister chromatids Chromatids connected by centromere

22 Stages of Mitosis Prophase Metaphase Anaphase Telophase

23 Prophase Chromosomes shorten & thicken
Nucleolus & nuclear envelope disappears

24 Prophase Spindle fibers formed from microtubules
Microtubules surround microtubule-organizing center (centrosome) Chromosomes attach to spindle fibers at kinetochore

25 Metaphase Pairs of sister chromatids align at center
Forms metaphase plate

26 Anaphase Chromatids separate at centromere
Chromatids pulled in two directions Chromosomes move toward poles Equally divides hereditary material

27 Telophase Cell readied for division (cytokinesis)
Spindle fibers disassemble Nuclear envelope reforms Nucleolus reappears

28 Cytokinesis Cell division after mitosis Cleavage furrow enlarges

29 Animal Cytokinesis Cell pinched in two (lack cell walls)
Pinching by microfilaments contracting

30 Plant Cytokinesis New cell wall must be laid down
Cell plate forms (Golgi Complex)

31 Mitosis

32 Cancer Deregulation of cell cycle Loss of control of mitosis
Result of mutation Over 200 types of cancer exists Number of cancer cases will double by 2050, as an increasing proportion of U.S. population reaches older ages

33 United States Cancer Death Rates

34 Characteristics of Cancer (no matter what type)
Uncontrolled cell growth- most significant characteristic of all cancer cells Loss of cell differentiation (specialization) Invasion of normal tissues, occupying space in which normal cells would otherwise reside Metastasis or spread to multiple sites




38 Stages of Cancer 1. Initiation 2.Promotion 3.Progression

39 Initiation of Cancer (Transformation)
Series of gene mutations damages DNA Proto-oncogenes become oncogenes (“on” switches for tumors or masses) Usually additional mutations are needed Affect tumor suppressor genes, ”off” switches These genes are inactivated, allowing cancerous growth Initiation does not directly result in cancer, it results in a precancerous cell. Heredity acts only as an initiator, not a promoter

40 Promotion of Cancer Cells are stimulated to grow & divide when they normally would not. It is a gradual process, unlike initiation Carcinogens – agents that both initiate & promote cancer Viruses Chemicals Radiation Benign cells Masses of partially transformed cells, confined & encapsulated Cells exhibit dysplasia-growth patterns char. of cancer cells

41 Normal Cells Dysplastic Cells

42 Progression of Cancer Cells become less differentiated
Cells invade other tissue Move to other areas of the body Called malignant cells


44 Meiosis Chromosome number halved Required for sexual reproduction
2N  N Required for sexual reproduction Starts with diploid parents

45 Homologues Homologous chromosomes
2 chromosomes, same linear gene sequence corresponding genes on the 2 chromosomes are called alleles, alternative forms of same gene

46 Results in 4 haploid daughter cells
Process of Meiosis Two stages: Meiosis I Meiosis II Results in 4 haploid daughter cells

47 Meiosis I Pairs line up = synapsis crossing over begins
Splitting homologous pairs, tetrads

48 Meiosis I Cross over – non sister chromosomes may cross over one another Chromatids may exchange segments

49 Stages of Meiosis I

50 Interkinesis Interphase-like period Between meiosis I and meiosis II
No DNA replication

51 Meiosis II Stages

52 Meiosis

53 Importance of Meiotic Recombination
Provides variability for offspring Essential to process of evolution



56 End chapter 12

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