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Reproduction
Chapter 4
Section 4-2
Reproduction
A process by which an organism produces
others of the same kind.
There are two kinds of reproduction
Sexual reproduction – uniting of sperm and
egg
Asexual reproduction – creating a new life
from one parent
-lower animals and plants
can reproduce in this manner.
Humans – sexual reproduction
Body cells have 46 chromosomes in every cell
Sex cells• Sperm cell – 23 chromosomes - father
• Egg cell – 23 chromosomes - mother
When sperm and egg unite it produces a child
with 46 chromosomes in each body cell.
Asexual reproduction - fission
New organisms are
produced from one
parent.
DNA or offspring is
identical to the DNA
of parent.
Mitosis is an example
of this form of repro.
Paramecium- asexual
Budding
Asexual repro found
in invertebrate animals
such as hydra, starfish,
sponges and worms
Hydra – small
freshwater tubular
organism.
Budding
Asexual form of repro
that allows bud to
grow out of the
hydra’s side, develop
mouth tentacles and
finally rip out of the
hydra’s side to
produce an offspring.
Regeneration
To grow new body
parts from a piece of
an animal.
Starfish
Strawberry plants use runners.
Plantlets: These
can take the form of
runners (eg
strawberries) or side
branches (busy
lizzy). New plant
developing from
strawberry runner
Cuttings of plants
Cuttings: We can
make cuttings or
grafts, which in the
right conditions will
develop roots and
grow into a new
plant.
Planarian
-repro by regeneration
Planarian
Identification:
•Flatworm with prominent eyes and a triangular head.
•Size: 5 - 20 mm.
•Creeps like a slug on the ground; swims by wriggling in snake-like
manner.
What it Eats:
•Predators that feed on a variety of tiny snails, worms, and
protozoans.
Interesting Facts:
•If you cut a planarian into pieces, each piece will regenerate into a
new planarian
Bacterial fission
Asexual reproduction
Bacteria reaches a certain size
DNA is copied
Splits apart producing two daughter cells
Bacterial cell division
Sexual Reproduction
Production of a new
organism when sex
cells from two parents
combine
Male – sperm
Small with whiplike
tails
• Flagella
• Used for movement
Head – almost all
nucleus
Contains 23
chromosomes
Female - egg
Large cell
Contains food for the
embryo
Contains 23
chromosomes
Meiosis
Production of sex cells
Each sex cell must contain half the amount
of chromosomes as a body cell
Takes place in both plants and animals
Importance of Sex Cells
In humans there are 23
pairs of chromosomes46 chromosomes
Each pair has 2
chromosomes that are
alike
Diploid – (double) a
cell that has 2 of every
chromosome
Sex cells
Haploid – contains
one chromosome from
each matched pair
- (half the
number)
Fertilization
Joining of an egg and
a sperm
Zygote – fertilized
egg
Zygote undergoes
mitosis to further
develop into the
offspring.
Egg cell surrounded
by sperm cells
Only one sperm can
enter an egg
Zygote results
Meiosis
This is the division of
sex cells.
There are two
divisions of meiosis
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Cell Division
Meiosis I
Prophase I – doubled
chromosomes and
spindles appear
- nuclear
membrane and
nucleolus disappear
- doubled
chromosomes tied
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Cell Division
Metaphase I – paired
chromosomes line on
middle of cell.
-centromeres
attach to spindles
Anaphase I – centromeres
detach and move to ends
of poles
Telophase I – cell divides
into 2 daughter cells
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Cell Division
Meiosis II
Prophase II –
spindles and doubled
chromosomes
reappear
Metaphase II –
doubled chromosomes
move to center of cell
Anaphase II – chrom
separate and move to
ends of cell.
Telophase II – spindles
fibers disappear and
nuclear membrane forms
around chrom at ends of
cell.
Each nucleus is haploid
Cell division occurs
forming 4 daughter cells
Results of meiosis
4 daughter cells with half the number of
chromosomes in each (haploid)