Mitosis/Meiosis

Cell Growth

• Reason: – Large cells create more of a demand on DNA– Trouble moving enough nutrients and wastes

across cell membrane

• Importance: cells regenerate– Repair/renew– Growth– reproduction

• Reproduction– Asexual • 1 parent• Simple cell division- cells duplicate genetic material,

splits into 2 new identical offspring

– Ex: Paramecium, sea stars

• Sexual Reproduction– 2 parents– Genetic material combine- offspring differ from

parents– Union of sex cells (egg + sperm)

• Ex: multicellular organisms, single celled organisms

• 2 types of cell division– Mitosis– Meiosis

Cell Cycle

• Chromatin- fibers containing protein + DNA• Chromosomes- chromatin condensed into

visible structures - thousands of genes

• Ex: Humans= 46 chromosomes

• Before cell division- chromosomes duplicate• Sister chromatids- identical copies joined• Centromere- joins chromatids

Cell Cycle• Birth of cell till time it reproduces• Interphase (90%)– G1 (gap)– S phase (synthesis)– G2

• M Phase (mitotic)• Cytokinesis

• Cytokinesis- cytoplasm divides– (1 nucleus, cytoplasm, plasma membrane)

Cytokinesis in Animal Cells

Cytokinesis in a Plant Cell

Mitosis

• http://www.youtube.com/watch?v=2WwIKdyBN_s&feature=related

• Spindle- microtubules that guide movement of chromosomes

• Centrosomes- spindles grow from here– Contain centrioles in animal cells

Draw stages of mitosis

• Pg 246-247• Draw each stage of mitosis, the drawing should be

neat and in color• Label each phase and include a detailed

description of what is occurring in each• Label– Centrioles - spindle– Chromatin - centromere– Chromosomes - sister chromatids– Nuclear envelope

Prophase• chromatin condenses into

chromosomes• Nuclear envelope breaks

down• Mitotic spindle forms • Centrioles move to opposite

sides of the cell

Metaphase• Chromosomes line up

across center of cell• Chromosomes attached to

spindle fibers by centrioles

Anaphase• Sister chromatids separate• Move toward poles by

spindles, microtubules shorten

• Microtubules also lengthen and push poles apart

Telophase• Chromosomes reach poles

of spindle• Spindles disappear• 2 nuclear envelopes reform• Chromosomes uncoil and

lengthen

Mitosis in a Whitefish

Mitosis in Animal Cells

Mitosis in a Plant Cell

Tumors and Cancer

• Out of control cell reproduction = mass of cells or tumor

• Benign Tumor– Removable by surgery– Cells remain at original site

• Malignant Tumor- masses of cells from reproduction of cancer cells

• Cancer- disruption of cell cycle• Metastasis- spread of cancer cells beyond

original site

Cancer Treatment

• Removed by surgery• Radiation therapy- high energy radiation

disrupts cell division• Chemotherapy- drugs which disrupts cell

division

Meiosis

• Cell division= 4 cells each– ½ the number of chromosomes as parent

• Occurs in sex organs

• Karyotypes- display of chromosomes– Each with twin that resembles size + shape– Inherit one chromosome of each pair from mother

and father= Homologous chromosome

Homologous Chromosome

• same sequence of genes• Control same inherited characteristics• Ex: eye color gene located on same place of

the homologous chromosomes but one gene may call for blue the other brown

• Humans- 23 homologous chromosomes– Females– Males

• Sex chromosomes – Male XY– Female XX

• Diploid (2n)- 2 homologous sets of chromosomes

• Haploid (n)- single set of chromosomes, produced by meiosis

n = 23 2n =46 2(23)=46

Fertilization- haploid cells fuse (egg + sperm)Zygote- fertilized egg - diploid

• Spermatogenesis- making sperm cell – all four cells develop into sperm

• Oogenesis –making an egg cell=one egg

Process of Meiosis

• Life cycles of all sexual reproducing organisms alter haploid and diploid stages

• Keeps chromosome # from doubling every generation

• Exchange of genetic material b/w homologous chromosomes

• 2 meiotic division– Meiosis I- homologous

chromosomes separated– Meiosis II- sister

chromatids are separated into haploid cells

Prophase I• HC stick together = 4

chromatids (tetrad)• Spindle attaches to tetrad• Crossing over- sister

chromatids exchange material

Metaphase I• tetrads move to middle of

cell and line up

Anaphase I• HC separate and move to

opposite ends

Telophase I and Cytokinesis• Chromosomes arrive at

opposite poles• Nuclear envelope begins

to form• Cytokineses occurs

forming 2 haploid cells

Prophase II• spindle forms and attaches

to centromeres

Metaphase II• chromosomes line up in

center

Anaphase II• sister chromatids separate

and move to opposite poles

Telophase II and Cytokinesis• Chromatids considered

individual chromosomes arrive at opposite poles

• Cytokinesis splits cells• Produce 4 haploid daughter

cells

Genetic Variation

• Assortment of chromosomes- happens by chance

• Formula for different combinations- 2ⁿ Ex: Humans 2²³ = 8 million possible combos

• Crossing Over- exchange of genetic material between homologous chromosomes– Occurs during prophase– Genetic recombination