Cell Reproduction Chapter 8. Chromosomes Section 8.1

Cell Reproduction

Chapter 8

ChromosomesSection 8.1

Definitions:

Chromosome: rod shaped structure made up of DNA and proteins

Sister Chromatids: identical halves of a chromosomes

Definitions:

Centromere: protein that holds sister chromatids together

Homologous Chromosomes: chromosomes that code for the same traits that come from your mother and your father

Definitions:

Chromatin: less tightly coiled strands of DNAUncoiled so that the cell can read the DNA to

direct the cell’s activities

Chromosomes only occur during cell divisionChromatin coils up to make chromosomes

All normal members of the same species have the same number of chromosomes in their body cells.

Ameba 50 Goldfish 94

Alligator 32

Garden Pea 14

Brown bat 44

Grasshopper 24

Bullfrog 26

Horse 64 Carrot 18

Human 46

Cat 32

Lettuce 18

Chicken 78

Onion 16

Chimpanzee 48

Redwood 22

Corn 20 Sand dollar 52

Earthworm 36

Fruit fly 8

Sex Chromosomes

Definition: chromosomes that determine the sex of the organismMay carry other genes as well

Humans: X and YMales: XYFemales: XX

Autosomes:

Definition: All other chromosomes in the body besides the sex chromosomes

Humans = 46 total chromosomes2 sex chromosomes44 autosomes

Karyotype – map of an organism’s chromosomes

http://www.chromosome18.org/AboutGenetics/BasicGenetics/WhatisaKaryotype/tabid/120/Default.aspx

Karyotype – map of a organism’s chromosomes

Cells having 2 sets of chromosomes are diploid (2N)

The haploid number of a human egg or sperm cell is 23, and there are no homologous chromosomes in either cell (1N)

Diploid and Haploid Cells

MitosisSection 8.2

Why Cells DivideCell size is limited

Cells cannot keep growing indefinitely

Replacement of damaged cells

Growth - embryoAsexual reproduction

Single celled life formsBinary fission

Sexual reproduction - meiosis

Eukaryotic Cell Division

Mitosis (Growth Division): Division of cell producing two identical daughter cells

2n 2n

Meiosis (Reduction Division): Division of cell producing four haploid daughter cells

2n 1n

The Cell Cycle (Life Cycle of the Cell)

2 Major Parts:1. Interphase

G1SG2

2. Cell DivisionMitosis –

nucleusCytokinesis –

cytoplasm

Part 1: Interphase

Stage your cells are in the most amount of time

When cell does its “normal” jobs

Contains 3 stages: G1, S, and G2

cell growth

DNA replicates

Growth and preparationfor mitosis

Mitosis

Cytokinesis

cell doubles in sizeenzymes and ribosomesand mitochondriadouble in number

rapid growth,synthesizing necessaryenzymes and structuresfor mitosis

G1 Phase

S Phase

G2 Phase

S Phase – DNA Replication

Process by which DNA builds an exact copy of itself

After replication has occurred, each double stranded molecule contains one old strand and one new strand of DNA

1879 Walter Flemming used red dye to observe cell structures during mitosis, it killed the cells and so he had to take pictures at each stage in order to come up with a pictorial model of mitosis.

Part 2: The Stages of Mitosis (page 156)

Mitosis – Step 1: ProphaseChromosomes (2 chromatids) form from

chromatin Nuclear membrane disassemblesCentrioles move to polesSpindle fibers form

Mitosis – Step 2: Metaphase

Chromosomes line up at the middle of the cell “Metaphase Plate”

- Stage where karyotypes are made from!

Mitosis – Step 3: Anaphase

Sister chromatids (from the same chromosome) separate and move to opposite poles

Mitosis – Step 4: Telophase

Spindle fibers disappearNuclear membrane forms againChromosomes go back into chromatin

form2 nuclei (diploid) per one cell

Cytokinesis

Division of cytoplasmCell membrane pinches in to form two

separate cellsResults: 2 IDENTICAL daughter cells

AnimationMitosis

Mitosis “Flip Book” To receive full credit you must:1. Illustrate what is going on in the life cycle

a) Title Pageb) Interphase: G1, S, G2

b) Mitosis: prophase, metaphase, anaphase, telophasec) Cytokinesis: early & lated) Finished product

2. Diploid # (2N) = 8 Haploid # (1N) = 4(represent homologous chromosomes with different

colors)Need help? Consult your book or your notes!

Cont…

3. Diploid # (2n) = 8

Haploid # (1n) = 4

4. Represent homologous pairs with 4 different colors.

Need Help? Consult you book or your notes!

offspring is an exact copy of parents - occurs in lower plants and animals

(bacteria, molds, algae and protozoa)

all cells form through mitosis

Asexual Reproduction

Asexual Reproduction

Regeneration Budding

Binary FissionSpores

Mitosis Slides

MeiosisSection 8.3

2 Stages: 2n

n n

nn n nResults in 4 haploid cells

Meiosis I

Meiosis II

Interphase

Same as mitosis!

3 Stages: G1, S, G2

Meiosis I

Formation of 2 haploid cells from 1 diploid cell

Production of gametes

“Reduction division”

Step 1: Prophase I

•Nuclear membrane breaks down

•Centrioles move to the poles, spindle fibers form

•Synapsis occurs, forming tetrads, allowing for crossing over (genetic variety)

Definitions:Synapsis: When a pair of homologous

chromosomes partner up inside a dividing cell

Tetrads: the name given to a partner of homologous chromosomes during synapsis

Crossing over: chromatids of homologous chromosomes twist around and trade places causing an exchange of DNA

Step 2: Metaphase I

Tetrads line up randomly at the metaphase plate

Step 3: Anaphase I

Tetrads are split and each homologue is moved toward opposite poles

Independent assortment: the random separation of maternal and paternal chromosomesResulting in genetic variety of offspring

Step 4: Telophase I

Nuclear membrane reformsSpindle fibers and centrioles disappear2 nuclei per cellEach nucleus now has HAPLOID number

of chromosomes2n 1n

Cytokinesis I

Splitting of the cytoplasm to produce 2 haploid daughter cells

Meiosis II

•NO interphase between meiosis I and II

•The production of 4 haploid cells from 2 haploid cells.

•EXACT same process as mitosis!

Step 1: Prophase II

Step 2: Metaphase II

Step 3: Anaphase II

Step 4: Telophase II

Cytokinesis II

End result = 4 haploid cells

Purpose: Gamete Production

Gamete: sex cells (egg & sperm)

Oogenesis – egg production

Spermatogenesis – sperm production

Sexual Reproduction: genetic diversity of offspring

Page 155

Sexual Reproduction

Each parent contributes genes to the offspring.

each offspring has a different set of inherited traits from the parents

gives offspring a better chance of surviving in a changing environment

Mitosis vs Meiosis

Mitosis 1 division2 daughter cellsExact copies of parent cellsDiploid to diploidPurpose

Growth RepairAsexual reproduction

Meiosis2 divisions4 daughter cellsEach uniqueDiploid to haploidPurpose

Make gametes/ sex cells

Leads to genetic variation

Cancer

Cell cycle control systemEnzymes in cell control when and where cells

divide

Malfunction in system means cells divide at inappropriate times and placesBenign tumor - abnormal mass of essentially

normal cellsStay at original site, don’t move

Cancer uncontrolled cell division

Cancer

Problem not only uncontrolled divisionMetastisis

Cancer cells can move to other sitesNew tumor at that site

Three treatmentsSurgery to remove tumorRadiation Chemotherapy

Last two aimed at controlling division

Cancer treatments

Radiation Disrupts cell divisionMost actively dividing cells are tumorCan damage normal cells- ovaries / testes

ChemotherapySome disrupt cell division TaxolTaxol freezes spindleVinblastineVinblastine prevents spindle formation

Cancer cells immortal in cell cultureNormal cells stop growing after 50 culture