Chapter 8: Cell Reproduction

ReviewOrganelles

CentriolesMade of microtubulesActs as anchors in cell division

Mitotic Spindle fibersTwo Main types

Kinetochore Fibers- Attach from centriole to centromere of chromosomes and assists in movement of chromosomesPolar Fibers – Extend from pole to pole and keep the shape of the cell during cell division

Nuclear envelopeDouble Phospholipid bilayer surrounding nucleusAllows selective passage of RNA and other material

NucleolusDense area where DNA is concentrated in the nucleus

Section 8.1Chromosomes

Chromosome StructureRod-shaped and made of DNA and proteins called histonesTwo full copies of DNAForm it takes before cell divisionHas two identical halves called chromatid

ChromatidHalf of the chromosomeOne full copy of DNAAttached in the center

CentromereCenter where chromatids areheld together

ChromatinLess tightly coiled DNA-protein complexTin = thin *Think spaghettiForm taken during transcription

Section 8.1Sex Chromosomes

Determine gender of the organismMay carry genes for other characteristicsEither X or YFemale = XX Male = XYOne pair (or two chromosomes)

AutosomesRemaining chromosomesContain genes for many traits22 pairs (or 44 chromosomes)

Section 8.1Homologous Chromosomes

Two copies of each autosomeOne copy from each parentSame size and shapeCarry genes for the same trait

KaryotypePhotomicrograph of chromosomesNotice there are 22 pairs of autosomes and 1 pair of sex chromosomesWhat is the gender of this organism?

Section 8.1Diploid

Cells that are diploid contain two autosomes from each homologous pair and two sex chromosomesAbbreviated as 2n

Memory key * di = twoOccurs in all cells except sperm and egg cells

HaploidCells contain only one set of chromosomesTherefore, half the number of chromosomes of a diploid cellAbbreviated as 1n

Memory key * hap = halfSperm cell (1n) and egg cell (1n) create a diploid cell (2n)

Section 8.1Notice high

number of chromosomes in fern compared to humans!

Section 8.1Homework

Review questions on p. 153 #1-5

Section 8.1 Review Answers

1. Name the proteins that DNA wraps around to form a chromosome in eukaryotic cells.• Histones.

2. How do the structure and location of a prokaryotic chromosome differ from that of a eukaryotic chromosome?• A prokaryotic chromosome consists of a

circular DNA molecule. Eukaryotic chromosomes are rod-shaped, associated with histone and nonhistone proteins, and found within the cell’s nucleus.

3. Does chromosome number indicate whether an organism is a plant or animal? Explain.• No. For example, chimpanzees have the

same number of chromosomes as potatoes or plums.

Section 8.1 Review Answers

4. Contrast sex chromosomes with autosomes.• Sex chromosomes determine the gender of

an organism. Autosomes are all of the other chromosomes in an organism.

5. Using Table 8-1, list the haploid and diploid number of chromosomes for each organism.

Section 8.1 Review Answers

Organism Diploid # Chromosomes Haploid # Chromosomes

Adder’s tongue fern 1262 631

Carrot 18 9

Cat 32 16

Chimpanzee 48 24

Dog 78 39

Earthworm 36 18

Fruit fly 8 4

Garden pea 20 10

Gorilla 48 24

Horse 64 32

Human 46 23

Lettuce 18 9

Orangutan 48 24

Sand dollar 52 26

Section 8.2Cell Cycle

Repeating set of events in the life of

a cellInterphase

Time between cell divisions

Three phases

G1 – Cell growth

S – DNA is copied

G2 – Growth and prep for cell division

Cell divisionTwo phases

Mitosis – Nucleus of the cell divides

Cytokinesis – Division of the cell’s cytoplasm

Section 8.2Cell Division

ProkaryotesRemember: Has cell wall, no nuclei, no membrane-bound organelles

Binary fissionDivision of prokaryotic cell into two offspring cells

Section 8.2Cell Division (cont’d)

EukaryotesMitosis

Division of the nucleus

Four stages (Prophase, Metaphase, Anaphase, Telophase)

CytokinesisIn animal cells, pinching of cell

membrane occurs

Cleavage furrow

In plants, cell plate formation

Section 8.2Control of Cell Division

Checkpoints = traffic signal

Three main checkpoints

G1 checkpoint

G2 checkpoint

Mitosis checkpoint

Section 8.2 (cont’d)

MitosisProphase

Tight coiling of DNA into chromosomes

Nucleolus and nuclear membrane break down

Centrosomes appear and move to opposite ends of the cell

Kinetochore fibers extend from kinetochore from each chromatid to centrosome

Metaphase = MiddleKinetochore fibers move chromosomes to center of cell

All chromosomes line up in a single file line

Section 8.2Anaphase

Chromosomes separate at the centromere and chromatids move to opposite poles

Chromatids are now considered individual chromosomes

TelophaseSpindle fibers disassemble

Chromosomes return to less tightly coiled chromatin state

Nuclear envelope forms around each set of chromosomes

Nucleolus forms in each of the newly forming cells

Animation

Mitosis vs MeiosisWhere do they occur?

Mitosis – in the body cells (Somatic Cells)Meiosis – in the germ cells (Sex Cells)

Why does it occur?Mitosis

Asexual reproductionGrowth and developmentTo replace old cells

MeiosisFormation of gametes (egg and sperm cells) that will be used in sexual reproduction

Mitosis vs MeiosisEnd result?

46

46 46

MITOSIS

46

23 23

23 23 23 23

MEIOSIS

MeiosisAlso known as reduction division

Occurs in germ cells found in the ovaries and testes

Produces sex cells which are haploid

Occurs in two phasesMeiosis I

Reduces the number of chromosomes from diploid to haploid

Meiosis IIProduces four haploid daughter cells

Meiosis I

Meiosis II

Section 8.3Results of mitosis vs. meiosis

Section 8.3

Development of Gametes

Spermatogenesis

Oogenesis

Polar bodies

Sexual reproduction

Why is meiosis important?

Increases genetic diversity in a population of species.

This helps to prevent organisms from mass extinction in the event of a plague or other disaster.

Allows animals to adapt to a changing environment (natural selection)