Cell Reproduction

Stem Cell Shakes In The News

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

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

Meiosis Produces 4 cells that are not identical to 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 (Life Cycle)

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

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

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

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 & nuclear envelope disappears

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

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 (cytokinesis) Spindle fibers disassemble Nuclear envelope reforms Nucleolus reappears

Cytokinesis Cell division after mitosis Cleavage furrow enlarges

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

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

Mitosis

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

United States Cancer Death Rates

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

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

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

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

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 Required for sexual reproduction 2N  N Required for sexual reproduction Starts with diploid parents

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

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

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

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