Chapter 9: Cell Reproduction Mitosis and Meiosis

Cell Division and Mitosis Cell division –increases the total number of cells in an organism What happens to cell division when growth stops? –Continues –New cells replace dead cells

Nucleus

The Cell Cycle What is it? –Series of cell divisions –DNA must be copied and divided exactly

What are we dividing? in nucleus DNA All body cells have 46! Chromosomes!

Chromosome Numbers Sex chromosomes –X and Y (2) Autosomes –Body chromosomes (44) Total Humans: 46

Turner Syndrome XO Female lacking one X chromosome Egg does not have the sex chromosome female typically sterile

Turner Syndrome symptoms Poor breast development Skin folds on neck Wide-spread nipples Elbow deformities Swollen ankles and feet No menstruation

Down Syndrome (trisomy-21) Error caused due to non-disjunction –Chromosome pairs do not separate properly during cell division

Downsyndrome traits? Skin folds on upper eye corners Poor muscle tone Enlarged tongue Short neck Broad and round head Flat nasal bridge

Klinefelter Syndrome (XXY) Extra X chromosome Male is typically sterile

Binary Fission Prokaryotes copy genetic information Two identical haploid cells

Terms: Diploid –Cells with two sets of chromosomes –2n –Body cells Haploid –Cells with one set of chromosomes –n–n –Sex cells

Karyotypes Pictorial spread of chromosomes Used to detect genetic abnormalities (Down Syndrome)

Chromosome structure Chromatin - less tightly coiled DNA

Chromosomes DNA coiled around histone proteins

Homologous Chromosomes Two copies of each autosome one from each parent –Same length –Same centromere position –Same genes

Mitosis- (IPMAT) Throughout life in all parts of the body, except sex cells 5 phases –Interphase (time between divisions) –Prophase –Metaphase –Anaphase –Telophase (cytokinesis)

Phases of the Cell Cycle Stage (in order) Description G1G1 Initial growth Increase in size & make new organelles etc. S DNA replication G2G2 Prepare for division, more growth M Nuclear (mitosis) & Cell division (cytokinesis) *G 0 Resting stage following G1 “Waits” here until it is ready to divide again Some cells cannot come out of G 0 Interphase

G 0 phase Cell exits cell cycle No copying of DNA No cell division –Nerve cells –Heart cells

Phases of the Cell Cycle S G2G2 G1G1 Checkpoints!

Interphase Non-dividing stage Nucleolus & nuclear membrane are visible Period of growth

Interphase 3 stages: –G1–G1 Period of rapid growth Cell size increase Organelles double –S–S DNA replicates –G2–G2 More growth

Prophase Nuclear membrane & nucleolus breakdown DNA coils into chromosomes (visible) Centrioles –Spindle fibers

Metaphase Chromosomes line up in the middle of the cell Spindle fibers attach to centromere

Anaphase Chromatids split at centromere Are considered individual Chromosomes Move to opposite poles

Telophase Chromosomes reach opposite ends 2 new nuclear membranes form Spindles disappear

Cytokinesis Division of the cytoplasm Division of organelles

Cytokinesis: Plants v. Animals 1.Plants: Cell plate forms and gives rise to a cell wall 2.Animals: membrane pinches in forming a cleavage furrow

Whitefish blastula mitosis anaphase metaphase telophase prophase interphase

Onion root tip mitosis anaphase metaphase telophase prophase interphase

Apoptosis  Programmed cell death  Cells going through apoptosis actually shrink and shrivel in a controlled process.

What happens when the Checkpoints don’t work? Cancer –uncontrolled growth and division of cells

Cancer Mutations –In genes called “oncogenes” –When 6 or 7 mutations occur = cancer Mutagens –Anything that causes cancer Environment UV rays X rays Chemicals

Cancer progression Metastasis

Angiogenesis Developing arteries and veins to “feed” the tumor

S G2G2 G1G1

Gametogenesis Gamete formation –Spermatogenesis –oogenesis

Fertilization Haploid gametes (n) fuse to form a diploid (2n) zygote. Sexual Reproduction = 46

Some Meiosis differences Occurs in reproductive cells Halves the number of chromosomes Four haploid gametes are produced Two successive nuclear divisions Exchange of genetic information

Meiosis I

Interphase I Period of Growth –Same as in mitosis

Prophase I Spindle fibers form Crossing-over –exchange of genetic material between homologous chromosomes

Crossing over

Crossing-over results in… Genetic recombination –New mixture of genes

Metaphase I Homologous chromosome pairs line up at middle of cell

Anaphase I Homologous chromosomes migrate to opposite poles

Telophase I Homologous chromosomes are at opposite poles Nuclear membranes form Cytokinesis

Meiosis II No more replication Separates identical chromatids Produces 4 haploid (n) cells (gametes)

Prophase II No crossing over Spindle fibers form

Metaphase II Individual chromosomes line up

Anaphase II Sister chromatids are pulled to opposite poles

Telophase II Nuclear membrane forms 4 haploid (n) cells (gametes)