Transcript Chapter 4: Reproduction of Organisms

Chapter 4: Reproduction of
Organisms
Life Science
7th grade
Inquiry
• Do you think ALL living things have two
parents?
• What might happen if the penguins (on
the chapter cover photo) did not
reproduce?
• Why do you think living things
reproduce?
Bell work Ch4. L1
• Sexual reproduction: reproduction in which the genetic
materials from two different cells combine, producing an
offspring.
• Egg: female sex cell that forms in the ovary.
• Sperm: male sex cell that forms in the testis.
• Fertilization: the process during which an egg cell and a sperm
cell join together to form a new cell.
• Zygote: The new cell that is formed as a result of fertilization.
• Diploid cell: Cells that have pairs of chromosomes
• Homologous chromosomes: pairs of chromosomes that have
genes for the same trait arranged in the same order
• Haploid cell: Cells that only have one chromosome from each
pair
• Meiosis: The process by which one diploid cell divides to make
four haploid cells
Launch Lab (work in pairs)
• Each pair gets one “male parent” and one “female
parent bag”
• Without looking in the bag, select three beads from
each bag.
– Record bead colors from each bag
– The six beads you pulled represent one offspring (x4)
– Put beads back in respective bags after each offspring
Offspring #1
Offspring #2
Offspring #3
Offspring #4
Male bag
Female bag
1- How are the offspring similar? How are they different?
2- Why were there differences between offspring? Are differences beneficial?
Why or why not?
What is sexual reproduction?
• Reproduction in which the genetic materials
from two different cells combine, producing an
offspring.
– Those cells are called sex cells
• Sex cells form in reproductive organs
• What are sex cells in humans and where do
they form?
Sex cells
• Egg
– Female sex cell
– Forms in ovary
• Sperm
– Male sex cell
– Forms in testis
Fertilization
• An egg cell and a sperm
cell join together
– This forms a new cell
– Zygote= new cell that forms
from fertilization
• Develops into an organism
• What process is
responsible for the
development of a zygote
into an organism?
Diploid cells
• Cells that have pairs of chromosomes
– Similar chromosomes occur in pairs
– This happens in body cells
– Diploid cells are produced via mitosis
• Video
Chromosomes
• Homologous chromosomes:
pairs of chromosomes that
have genes for the same
trait arranged in the same
order
– One from mom, one from dad
make up a pair
• *****NOT IDENTICAL=
DIFFERENT FROM
SISTER
CHROMATIDS.******
DO YOU THINK A
MORE COMPLICATED
ORGANISM HAS MORE
CHROMOSOMES THAN
A SIMPLER
ORGANISM?
How many chromosomes?
• Human body cells have 23
pairs of chromosomes= 46
total chromosomes
– Number of chromosomes
does NOT correlate with how
complicated an organism is
• Dog has 78, Fern has 1,260
chromosomes
Haploid cells
• Cells that only have one
chromosome from each pair (in
humans have 23 total, not 46 total)
• Sex cells are haploid
• Haploid cells are produced via
meiosis
Meiosis overview
• Many similarities to mitosis
• Mitosis+cytokinesis = ONE division of nucleus + one
division of cytoplasm
• End result= Two diploid cells
• Meiosis= TWO divisions of nucleus and TWO divisions
of cytoplasm
• End result= FOUR haploid cells
• Happens in two phases- meiosis I and meiosis II
Meiosis - phases
• Interphase- EXACTLY THE SAME
AS IN MITOSIS. Period of growth
and replication. Chromosomes are
duplicated and each duplicated
chromosome has two sister
chromatids joined at the centromere.
– This only happens once
Meiosis I - phases
• Prophase I:
chromosomes
condense,
homologous
chromosomes form
pairs. Nuclear
envelope breaks
apart, nucleolus
disappears.
Meiosis I - phases
• Metaphase I:
Homologous
chromosomes line up
along the middle of
the cell. Spindle fiber
attaches to
centromere.
Meiosis I - phases
• Anaphase I:
Chromosomes pairs
(homologous
chromosomes) are
pulled apart. SISTER
CHROMATIDS
STAY TOGETHER.
Meiosis I - phases
• Telophase I: Nuclear
membrane
reappears around
PAIRS of
chromosomes,
nucleolus reappears.
Cytoplasm divides
through cytokinesis.
Two daughter cells
form.
Meiosis II - phases
• NO SECOND
INTERPHASE. Daughter
cells from meiosis I
immediately undergo
meiosis II
• Prophase II: Because no
replication, chromosomes
stayed as thick sister
chromatids
– Nuclear envelope breaks
down
– Nucleolus disappears.
Meiosis II - phases
• Metaphase II:
– Sister chromatids
line up along the
middle of the cell
– Spindle attaches
to centromere.
Meiosis II - phases
• Anaphase II:
Sister chromatids
pulled apart and
move toward
opposite ends of
the cell
Meiosis II - phases
• Telophase II:
– Nuclear
membrane forms
around
chromosomes
– cytoplasm divides
via cytokinesis.
• Result= four
haploid cells.
Meiosis summary
Interphase
Cell growth and replication. Sister chromatids attached at
centromere.
Prophase I
Homologous chromosomes form pairs, nuclear membrane
breaks apart, nucleolus disappears
Metaphase I
Homologous chromosomes line up in center of cell, spindle fiber
attaches to each chromosome
Anaphase I
Homologous chromosomes pulled apart towards opposite ends
of the cell. SISTER CHROMATIDS stay together.
Telophase I
Nuclear membrane forms around sister chromatids, cytokinesis
divides cytoplasm. Two daughter cells formed.
Prophase II
Metaphase II
Nuclear membrane breaks apart, nucleolus disappears.
Anaphase II
Sister chromatids pulled apart towards opposite ends of cell.
Telophase II
Nuclear envelope reappears around individual chromosomes,
nucleolus reappears. Cytokinesis divides cell.
End Result:
FOUR haploid cells
Sister chromatids line up along metaphase plate, spindle fiber
attaches to centromere.
Why is meiosis important?
• Maintains diploid cells
– When haploid cells join (via fertilization) they make
a diploid cell= zygote.
– Zygote then divides via mitosis to make the
organism
• Creates haploid cells
– Maintains correct number of chromosomes in sex
cells so when they join, they form a zygote with
the correct number of chromosomes
Mitosis vs Meiosis (table p.122)
Characteristic
Number of
chromosomes in parent
cell
Meiosis
Mitosis and Cell
division
Diploid
Diploid
Reproductive
Body
Number of divisions of
nucleus
2
1
Number of daughter
cells produced
4
2
Haploid
Diploid
Forms sperm and egg
cell
Growth, cell repair, some
kinds of reproduction
Type of parent cell
Chromosome number
in daughter cells
Function
Advantages of sexual
reproduction
• Genetic variation
– Inherit different genes from parents compared to
siblings
– Occurs in all organisms that reproduce sexually
• Includes plants
• Selective breeding
– Choose the traits you like (breed individuals with
those traits) and over time those can become
dominant
• Video
Disadvantages of sexual
reproduction
• Takes time and energy
• Search for mate can be problematic
– Expose to predators, disease or harsh
environments
• Limitations
– Gestational period (pregnancy)
• Can’t get pregnant while already pregnant, have to
wait for one to finish before can start another one
ONE STEP UP: Can you think of a
way some organisms overcome the
gestational limitation?
HOMEWORK Ch4 L.1
• Vocabulary words on flash cards
– Memorize for quiz
• Lesson review questions p.126 #1-10
• Outline lesson 1
• Quiz lesson 1
Meiosis lab p.138
• Let’s recreate mitosis and meiosis using pool
noodles
• 8 volunteers to be chromosomes
– Each person gets one
• 8 volunteers to be nuclear envelope
– Surrounds chromosomes
• 8 volunteers to be spindle
• 8 volunteers to be narrators/puppeteers
Bell Work Ch4 L.2
• Asexual reproduction: the process by which one parent
organism produces offspring WITHOUT meiosis and fertilization
• Fission: cell division in prokaryotes that forms two genetically
identical cells
• Budding: the process by which a new organism grows by
mitosis and cell division on the body of its parent.
• Regeneration: occurs when an offspring grows from a piece of
its parent
• Vegetative reproduction: a form of asexual reproduction in
which offspring grow form a part of a parent plant
• Cloning: a type of asexual reproduction performed in a
laboratory that produces identical individuals from a cell or from
a cluster of cells taken from a multicellular organism
Yeast launch lab p.129
• I warmed water to 34˚C (93˚F)
• I added 5g yeast and 5g sugar
• What does the mixture look like initially? After
5 minutes?
• Drop of solution onto slide (cover with cover
slip)
• Draw what you see under microscope.
• Evidence of reproduction?
• TURN THIS IN
What is asexual reproduction?
• One parent organism
produces offspring WITHOUT
meiosis and fertilization.
– Inherit all DNA from one parent
• What are some
advantages/disadvantages of
reproducing this way?
• Mold: a type of fungus that can
reproduce sexually OR
asexually. (fuzzy stuff on old
food)
• Bacteria, protists, plants and
some animals can reproduce
asexually
ONE STEP UP: How do
parent/daughter cells compare
to each other in asexual
reproduction?
Types of asexual reproduction
•
Fission: cell division in
prokaryotes that forms
two genetically identical
cells.
1. Prokaryote’s DNA is copied
2. Each copy attaches to cell
membrane
3. Cell elongates, pulling
copies of DNA apart
4. Cell membrane pinches
inward along middle of the
cell
5. Cell splits and forms two
new identical offspring
•
Example: E.coli
Types of asexual reproduction
• Mitotic cell division:
used by unicellular
eukaryotes
– Organism produces
two offspring
through mitosis and
cell division
• Example: amoeba
Types of asexual reproduction
• Budding: a new
organism grows by
mitosis and cell division
on the body of its
parent.
– Bud is genetically
identical to parent
– When bud gets big
enough, it can break off
from parent
• Example: hydra
(multicellular organism),
yeast (unicellular
organism).
Types of asexual reproduction
• Animal regeneration: occurs when an offspring
grows from a piece of its parent. (varies greatly
among animals)
– Producing new organisms: each new organism is
identical to starting organism
• Example: planarian (can cut in half and each half makes a new
organism), sea star (can cut an arm and if it contains part of
central disk and conditions are right, that arm will make a whole
new star)
Types of asexual reproduction
• Animal regeneration
cont’d
– Producing new parts:
regeneration
• Common in animals.
Humans can regenerate
skin or liver, some animals
can regenerate limbs.
• THIS IS NOT
CONSIDERED ASEXUAL
REPRODUCTION
BECAUSE IT DOES NOT
PRODUCE A NEW
ORGANISM
Types of asexual reproduction
•
Vegetative reproduction: a
form of asexual
reproduction in which
offspring grow form a part of
a parent plant.
1. Parent plant can grow long
stems called stolons
2. If a stolon touches the ground, it
forms roots.
3. Once roots are down, a new
plant can grow.
4. If stolon is broken from parent
plant, the new plant can survive
on its own.
– Example: strawberries,
raspberries and potatoes.
Types of asexual reproduction
• Cloning: a type of
asexual reproduction
performed in a
laboratory that
produces identical
individuals from a cell
or from a cluster of
cells taken from a
multicellular
organism.
Types of asexual reproduction
•
Plant cloning: do via tissue
culture.
–
•
Animal cloning (Example:
sheep)
–
–
–
–
–
–
•
Use cells from meristem to grow
new plants in lab
Take cell from sheep 1, take
unfertilized egg from sheep 2
Remove DNA from unfertilized egg
(it’s an empty egg now)
Fuse cell from sheep 1 with empty
egg from sheep 2
Cell develops into embryo in
laboratory
Implant embryo into sheep 2
Sheep 2 gives birth to clone of
sheep 1
Video
Advantages of asexual
reproduction
• Don’t need a
mate
• Rapidly
produce a
large number
of offspring
Disadvantages of asexual
reproduction
• Genetically identical
to parent= little
variation within a
population
– Variation can give
better chance of
survival
• Mutations
– Harmful mutations will
be passed on to all
offspring
HOMEWORK Ch4 L.2
• Vocabulary wordsß on flash cards
– Memorize for quiz
•
•
•
•
Lesson review questions p.137 #1-9
Outline lesson 2
Quiz lesson 2
OPTIONAL: Extra credit (due on test day)
p.141-145 (all)
– You MUST write the entire question and answer
down for credit. Only answers will NOT be
accepted.