genetic basis of life(mitosis and meiosis)

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