Transcript Cell Reproduction

CELLULAR REPRODUCTION
This is the making of cells
--not necessarily making babies
HEY YOU WANNA
SPLIT?
Why do Cells Divide?
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1. maintain surface area to volume ratio
2. growth of organism
3. repair damaged areas
4. replace worn out cells
5. pass on genetic information
2 Forms of Cellular Division
• Asexual Reproduction
• Sexual Reproduction
Asexual Reproduction
• production of new cells from one parent
cell
• offspring cells identical to parent cell
• can make new cells or an entire organism
Asexual production of whole
organisms
1. BINARY FISSION
-cell divides into two equal cells
-occurs in bacteria and blue-green algae
and paramecia
2. SPORES
-groups of cells form inside parent
-cells burst out of parent and grow into new
organisms
-occurs in fungus and ferns
3. BUDDING
-division into two unequal parts
-smaller cell will then grow to size of parent
-occurs in fungus (yeast) and hydras
4. VEGETATIVE PROPAGATION
-part of the parent will break off and grow
into a completely new organism
-common in plants
(spider plants, potatoes)
Asexual reproduction for growth,
repair, and replacement of cells
• Terms To Know
• CHROMOSOME: structure that contains
the DNA
• CHROMATIN: thin, stringy form of DNA
where the molecule is relaxed and
unwound into thread-like fibers
Chromosome
Structure
CHROMATID: the
tightly wound, visible
form of a chromosome
SISTER
CHROMATIDS: 2
identical
chromosomes, the
original and its copy
• CENTROMERE: the point where sister
chromatids are connected
How many chromosomes do
we have?
• 46- (23 pairs)- called the diploid
number (2n=46)
• Where did these come from?
• Each Pair= 1 from mom & 1 from dad
Asexual reproduction for
growth, repair, and replacement
of cells
• Cells go through a cell cycle
• Then………
• Cells split to form new cells and
maintain chromosome number
BRAINTEASER
• If each cell has 46 chromosomes, what
has to happen each time before a cell
divides?
The Cell Cycle
Fig. 9.3, p. 151
Interphase
• stage of growth / preparation for
division
• lasts about 21 hours
• DNA in Chromatin
form
• 3 stages: G1, S, G2
Stages of Interphase
• G1- period of growth / development
• S (synthesis) duplicates DNA (chromosomes)
– still in chromatin phase
• G2 duplicates cytoplasm and organelles
HOW DO CELLS DIVIDE?
Answer= MITOSIS
Mitosis completes the cell cycle
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis
• chromosomes
become visible
chromatids
• sister chromatids
form (seen as X)
• microtubules form
from a spindle at
opposite ends of the
cells
• spindle arises from
centrioles
• nuclear envelope
disappears
Prophase
By the end of
prophase…
• microtubules have
attached to
centromeres
• sister chromatids
being pulled
toward center of
cell
Metaphase
• microtubules pull
chromatids to
center
• chromatids align
along the center of
cell
Anaphase
• Chromosomes split
at centromeres
• microtubules pull
apart chromosomes
• Chromosomes
(chromatids) begin
migrating to
opposite ends of
cell
• Chromatids arrive
at poles
• nuclear envelope
reforms around
chromatids
• chromatids unwind
into chromatin
• spindle
disintegrates
• cell membrane
begins forming in
center
Telophase
Cytokinesis
• cell membrane finishes splitting the cell
• 2 daughter cells are formed
• cells will be slightly smaller than parent
cell
INTERPHASE
nucleus
cytoplasm
one spindle pole
one of the
condensed
chromosomes
spindle equator
microtubules
organized as a
spindle
apparatus
TELOPHASE
PROPHASE
one spindle pole
Plant Mitosis
METAPHASE
ANAPHASE
CELL AT INTERPHASE
EARLY PROPHASE
cell
chromosomes
nucleus
LATE PROPHASE
PROMETAPHASE
Animal Mitosis
microtubules
pair of
centrioles
plasma
membrane
nuclear
envelope
Fig. 9.5a, p. 152
METAPHASE
ANAPHASE
TELOPHASE
INTERPHASE
Fig. 9.5b, p. 153
Sexual Reproduction
• Key Facts
• sex cells are formed – called Gametes
(Meiosis)
• fertilization results in offspring
• offspring exhibits traits of both parents
Points of Interest
• all cells contain 2 of each chromosome- 1 from
mom and 1 from dad
• each of the pair carries identical genes
• variation exists in the outcome of the genes
– example: eye color
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humans have 46 chromosomes (23 pairs)
22 pairs are called autosomes
The 23rd pair is the sex chromosomes (X and Y)
Males= XY Females= XX
More Terms
• DIPLOID: the total number of
chromosomes a species carries
– often abbreviated as 2n
– found only in parent cells
• HAPLOID: half the number of
chromosomes for a species
– often abbreviated as n
– found in sex cells (egg/sperm) formed from
meiosis
• HOMOLOGOUS CHROMOSOME: 2
chromosomes which are the same
(1 from mom 1 from dad)
– Both found in diploid cells
– often described as “homologues”
• GAMETE: the sex cell formed from
meiosis
– haploid condition
– egg or sperm
MEIOSIS
• begins with the cell cycle
• 2 Phases
– MEIOSIS I
– MEIOSIS II
• Occurs only in Gonads- testes and ovaries
• Remember-Mitosis occurs in all other
Somatic (body) cells
• Reduces the number of chromosomes by
half
Interphase
• a stage of growth and preparation for
division of nucleus
• DNA is in Chromatin form
• 3 stages: G1, S, G2
• the DNA(chromosomes) does double
MEIOSIS I
• very similar to Mitosis
• stages include
– Prophase I
– Metaphase I
– Anaphase I
– Telophase I
– Interkinesis**
Prophase I
• chromatin shortens and thickens into
chromatids (sound familiar?)
• since there are 2 of each chromosome,
the 2 homologous chromosomes pair
up to form a TETRAD *(does not
happen in Mitosis)
Brain Teaser
• You are the world’s leading tomato
researcher. You have located the gene
in a tomato’s DNA that produces
lycopene, a natural chemical that helps
fight heart disease. The gene is on
chromosome 10. If a tomato has a
diploid # (2n) of 24, how many tetrads
will you have to search through during
prophase 1 until you locate
chromosome 10?
Metaphase I
• the tetrads will align along the centersimilar to mitosis
• Different arrangements can be formedsee example on board
Anaphase I
• the tetrads break
• one of each chromosome and its sister
chromatid will remain attached
• the sisters will migrate toward the
poles
Telophase I
• cytoplasm will separate as in Mitosis
• the sisters remain attached at the
centromere
• chromatids do not relax into chromatin
Interkinesis
• the DNA is not duplicated
• this is a period between 2 phases
• each cell has completed the first
division
• each cell is haploid (n)
MEIOSIS I
plasma
membrane
newly
forming
microtubules
in the
cytoplasm
PROPHASE I
spindle
equator
(midway
between the
two poles)
one pair of
homologous
chromosomes
METAPHASE I
ANAPHASE I
TELOPHASE I
Fig. 10.4a p. 164
then…MEIOSIS II
• similar steps occur again except the cell is
going to split the sister chromatids into
two sets
• *no Interphase II
• stages include
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Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis
but...
• in Anaphase II, the sister chromatids
are split apart
• one of each migrates to opposite poles
• during Telophase II, the nucleus forms
around the chromosomes (chromatids)
• chromatids relax into chromatin
MEIOSIS II
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
Fig. 10.4b p. 165
Cell Division has finished
• the “daughter” cells produced are in
the haploid condition
• 1 cell has now produced 4 haploid
daughter cells
• they need to be finished
Formation of the Egg and
Sperm
• In Females• OOGENESIS - formation of the egg
– 1 cell makes 4 daughter cells
– only 1 daughter becomes the egg
– cell division is not equal -3 become POLAR
BODIES
– all will be haploid
• SPERMATOGENESIS - formation of
sperm
– 1 cell makes 4 equal sized daughter cells
– all 4 will be sperm
– all will be haploid
Fertilization
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is not part of cell division
occurs when an egg and sperm meet
a ZYGOTE forms from the meeting
the zygote is 2n- chromosomal number is
restored
Function of Fertilization
• produces new offspring
• introduces mutations for survival
• increases variation in a population
Twins
• 2 Types
• Identical- always same sex- after being
fertilized, zygote splits spontaneously and
both begin dividing (MONOZYGOTIC)
– Identical DNA
• Fraternal- 2 eggs are present to be
fertilized- can be same or different sexesappear different because DNA is different
(DIZYGOTIC)