Cellular Reproduction

Ch. 8

(8-1) Chromosomes

• DNA & protein in a coiled, rod-shaped form that occurs during cell division– Uncoiled form is chromatin

• Histone: protein DNA wraps around– Maintains shape & tight packing

Chromosomes (cont.)

• 2 sister chromatids– Exact copies of each other

• Connected by centromere

• Cell division separates chromatids

• Each new cell gets 1 copy of each chromosome

Chromosome #

• Each species has characteristic # of chromosomes in each cell

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

• Determine sex of organism & may carry genes for other characteristics– Humans (X or Y)

• Autosomes: all other chromosomes besides sex– Humans = 44 (other 2 are sex)

Homologous Chromosomes

• Homologues: pairs of chromosomes– Same size, shape, & genes– Different from other homologues

• In sexual reproduction, organism receives 1 copy of each autosome from each parent

Karyotype

• Photomicrograph of chromosome in a living cell– Humans: 22 homologues & 2 sex chromo.’s

Diploid

• (2n): cells that contain 2 sets of chromosomes– Humans 2n is 46

• Haploid (1n): cells that contain 1 chromosome of each hom. pair– Sex chromo.’s

Reproduction

• When sperm (1n) & egg (1n) combine to make 1st cell of new organism, the new cell is diploid (2n)

(8-2) Cell Division

• Process in which cells produce offspring cells

• Why do cells divide?– Size is limited – Replace damaged cells– Growth

Prokaryotic Cell Division

• Binary fission: division of prokaryotes into 2 offspring cells

• 3 stages:1. Chromosome copied

2. Cell grows

3. Cell wall forms & cell splits into 2 new identical cells

Eukaryotic Cell Division

• Mitosis (Growth Div.): division of cell producing 2 identical daughter cells– 2n 2n

• Meiosis (Reduction Div.): division of cell producing 4 haploid daughter cells– 2n 1n

The Cell Cycle

1. Interphase• G1

• S

• G2

2. Cell Division• Mitosis (M phase): nucleus divides• Cytokinesis: cytoplasm divides

Interphase

• Cells in this stage most– Time b/w cell divisions

• 3 stages– G1: offspring grow to mature size

• G0: leave cycle, usually when mature

– S: DNA replication

– G2: cell preps for cell division

DNA Replication

• After replication, each double stranded molecule contains 1 old strand & 1 new strand of DNA

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

Step 1: Prophase

• Chromo.’s form from chromatin

• Nuclear membrane disassembles

• Centrioles move to pole

• Spindle fibers form

Step 2: Metaphase

• Fibers line chromo.’s up in the middle of the cell

• Metaphase plate

Step 3: Anaphase

• Sister chromatids separate (become individual chromo.’s) & move to opposite poles

Step 4: Telophase

• Spindle fibers disappear

• Nuclear membrane reforms

• Chromo.’s go back to chromatin

• 2 nuclei per 1 cell

Cytokinesis

• Division of cytoplasm– Animals - cell membrane pinches – Plants - cell plate forms

• Results: 2 identical daughter cells

Cancer

• Uncontrolled growth of cells

• Don’t respond normally to body’s control mechanisms

• Mutations can interfere w/ ability to slow or stop cell cycle

Brain Cancer

(8-3) Meiosis

• Nuclear division that reduces the # of chromo.’s in new cells to ½ the # of the original cell

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

• Prep for meiosis I

Meiosis I

• 2 haploid cells form from 1 diploid cell

• “Reduction Division”

Step 1: Prophase I• Chromo.’s form from chromatin• Nuclear membrane breaks

down• Centrioles move to poles• Spindle fibers form• Synapsis occurs

Definitions

• Synapsis: pairing of homologues to form tetrad

• Crossing over: chromatids of hom. chromo.’s twist & trade places to exchange DNA (genetic recombination)

Step 2: Metaphase I

• Tetrads line up randomly at the metaphase plate

• Spindle fibers attach

Step 3: Anaphase I

• Tetrads split & each homologue is moved toward opposite pole

• Independent assortment: random separation of maternal & paternal chromo.’s– Genetic variety

Step 4: Telophase I

• Nuclear membrane reforms

• Spindle fibers & centrioles disappear

• Each nucleus now has haploid # of chromo.’s

Cytokinesis I

• Cytoplasm splits to produce 2 haploid daughter cells

Meiosis II

• No interphase b/w meiosis I & II

• 4 haploid cells produced from 2 haploid cells

• Exact same process as mitosis

Step 1: Prophase II

• Spindle fibers form & begin to move towards middle of the cell

Step 2: Metaphase II

• Chromo.’s move to midline

Step 3: Anaphase II

• Chromatids separate & move to opposite poles

Step 4: Telophase II

• Nuclear membrane forms around chromo.’s in each of 4 new cells

Cytokinesis II

• End result =

4 haploid cells

Gamete Production

• Gamete: haploid sex cells – egg & sperm

• Oogenesis: egg production– 1 large egg & 3 polar bodies

• Spermatogenesis: sperm production– 4 sperm

Sexual Reproduction

• Each parent contributes genes & offspring is different from any other member of their species (except id. twin)

• Gives offspring better chance of surviving in a changing environment

Asexual Reproduction

• Offspring is an exact copy of parent– All cells form through mitosis

• Mainly occurs in prokaryotes– Bacteria, molds, algae, & protozoa

Regeneration Budding

Binary FissionSpores

Asexual Reproduction

Mitosis vs. Meiosis

• Mitosis– 1 division– 2 daughter cells– Exact copies of

parent cells– Diploid to diploid– Purpose:

• Growth• Repair• Asexual

reproduction

• Meiosis– 2 divisions– 4 daughter cells– Each unique

– Diploid to haploid– Purpose:

• Make gametes• Genetic

variation