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Cell ReproductionCell Reproduction
Stem Cell ShakesIn The News
Dividing Nuclear Material
• Cells must accurately separate genetic material during cell reproduction
• Methods– Mitosis – Meiosis
Mitosis
• Produces two identical cells
• Each cell has full DNA complement
• Used for growth and repair of somatic cells
Meiosis
• Produces 4 cells from parent cell
• Daughter cells have half genetic complement
• Produces gametes (sex cells)
Animal Life Cycle
• Egg = female gamete
• Sperm = male gamete
• Zygote – Fusion of egg & sperm– Full complement of
genetic material
Diploid Cells (2N)
• Full genetic complement
• 23 pair of chromosomes in humans
Haploid Cells (N)
• Produced during meiosis
• Contain only one set of chromosomes
• Reduction of chromosomes allows for combination to form diploid zygote
Fertilization
• One sex cell from each parent joins
• Creates diploid zygote
• Process is called sexual reproduction
Animal Life Cycles• Diploid phase dominates
• Gametes live hours to days
Plant Life Cycles
• Most have multicellular haploid phase
• Phase names– Gametophyte = haploid– Sporophyte = diploid
• Either phase can dominate, depending on plant type
Single Cell Eukaryote Reproduction
• Reproduce by mitosis
• Called asexual reproduction
• Produced two identical organisms
Asexual Reproduction• All single cell eukaryotes
• Some plants
• Some animals
Cell Cycle
Interphase
• Most of cell cycle
• Cell grows
• Organelles replicated
• DNA replicated
• Readies for mitosis
• Condenses DNA
G1 Interphase
• Cell growth
• Normal life functions
S Interphase
• DNA replicated
G2 Interphase
• DNA condenses into chromosomes– Strands = sister chromatids– Chromatids connected by centromere
Stages of Mitosis
• Prophase
• Metaphase
• Anaphase
• Telophase
Prophase
• Chromosomes shorten & thicken
• Nucleolus disappears
Prophase• Spindle fibers formed from microtubules• Microtubules surround microtubule-
organizing center (centrosome)• Chromosomes begin to move apart
Metaphase
• Pairs of sister chromatids align at center– Forms metaphase plate
Anaphase• Chromatids separate at centromere
• Chromatids pulled in two directions
• Chromosomes move toward poles
• Equally divides hereditary material
Telophase• Cell readied for division
• Spindle fibers disassemble
• Nuclear envelope reforms
• Nucleolus reappears
Cytokinesis• Cell division after mitosis
• Cleavage furrow enlarges
Animal Cytokinesis• Cell pinched in two
• Pinching by microfilaments contracting
Plant Cytokinesis• New cell wall must be laid down
• Cell plate forms
Mitosis
Cancer
• Deregulation of cell cycle
• Loss of control of mitosis
• Result of mutation
• Over 200 types
United States Cancer Death Rates
Characteristics of Cancer
• Uncontrolled cell growth
• Loss of cell differentiation
• Invasion of normal tissues
• Metastasis = spread
Stages of Cancer
• Initiation
• Promotion
• Progression
Initiation of CancerTransformation
• Series of gene mutations
• Proto-oncogenes become oncogenes
• Usually additional mutations are needed– Affect tumor suppressor genes– Turn off cell “off” switch
Promotion of Cancer
• Cells are stimulated to grow & divide
• Carcinogens – initiate & promote cancer– Viruses – Chemicals – Radiation
• Benign cells – Masses of partially transformed cells– Cells exhibit displasia
Normal Cells
Dysplastic Cells
Progression of Cancer
• Cells become less differentiated
• Cells invade other tissue
• Move to other areas of the body
• Called malignant cells
Meiosis
• Chromosome number halved– 2N N
• Required for sexual reproduction
• Starts with diploid parents
Homologues• Homologous chromosomes
• 2 chromosomes, same linear gene sequence
Process of Meiosis
Two stages:Meiosis IMeiosis II
Results in 4 haploid daughter cells
Meiosis I
• Splitting homologous pairs
• Pairs line up = synapsis
Meiosis I• Cross over – non sister chromosomes
may cross over one another
• Chromatids may exchange segments
Stages of Meiosis I
Interkinesis
• Interphase-like period
• Between meiosis I and meiosis II
• No DNA replication
Meiosis II Stages
Meiosis
Importance of Meiotic Recombination
• Provides variability for offspring
• Essential to process of evolution
End chapter 12