Transcript Chapter 10

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 doubles in size
enzymes and ribosomes
and mitochondria
double in number
cell grow th
Cytokinesis
Mitosis
DNA replicates
Grow th and preparation
for mitosis
rapid grow th,
synthesizing necessary
enzymes and structures
for 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
Meiosis I
n
n
Meiosis II
Results in 4 haploid cells
n
n
n
n
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
Asexual Reproduction
Regeneration
Spores
Budding
Binary Fission
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