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
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