Transcript Advantages of Sexual Reproduction

Sexual Reproduction
Why Sex?:
http://www.youtube.com/watch?v=gRpEt61XM4M&safe=active
• Monoploid gametes (n) are produced by
meiosis or “_____________” with half the
chromosomal material as the parent cell
– ________________________________ takes
place resulting in greater genetic variation
• ________________
(egg/sperm) come
from 2 separate
parents.
• Gametes fuse
together during
_________________
creating a _________
(diploid 2n)
• Advantages of Sexual Reproduction:
– Offspring genetically _________from parents
– This variation means that even if changes in
environment occur some offspring may
survive (__________________)
Sexual Reproduction
in Simple Organisms
• Conjugation:
– often found between ____
___________________ like
bacteria
– Bridge of cytoplasm between
cells allows exchange of
genetic material
• Can occur even though the
species normally reproduces
asexually through binary fission
Sexual Reproduction in Animals
• Usually involves two different sexes
• Gametes develop in specialized organs
(_____________)
• Ovaries produce eggs (n) (ova)
– Usually larger, round and ______________
– Often contain stored food in the form of yolk
• Testes produce sperm (n)
– Usually motile
– Has a head (containing DNA), middle
(containing Mitochondria) and tail (flagellum)
– Head has _____________________, helps
penetrate egg
Gametogenesis (meiotic division)
• Oogenesis: one primary sex cell develops into
_________________and several __________
Gametogenesis (meiotic division)
• Spermatogenesis: one primary sex cell
develops into _________________
• Hermaphrodites
– Have _________________________
– Usually found in animals that _____________
and it may be hard to locate mates
– Two animals meet and fertilize each other
• Ex: earthworm
Fertilization
• Monoploid sperm (n) & Monoploid egg (n) come
together to make ____________ zygote (2n)
– All _______________________ in zygote come from egg
– Membrane forms around egg after fertilization preventing
other sperm from entering
External
Fertilization
• _______________ outside
body of female.
• Requires ______________ for
sperm to swim to egg
– Often occurs with aquatic animals
• ___________ numbers of eggs
and sperm are released to
increase chance of fertilization
• Timing of release controlled by
hormones and sexual signaling
– Ex: _______________& _______
Internal
Fertilization
http://www.youtube.com/watch?v=bRKdTAzPBv0&safe=active
http://www.united-academics.org/magazine/earth-environment/topten-weirdest-animal-penises/
• Fusion of gametes occurs within moist __________
environment of female’s reproductive tract
• Occurs in ________________________________
– terrestrial vertebrates
– Allowed for a way for animals to evolve to live on land!
• Requires specialized sex organ to carry sperm from
males body to females (____________)
• Seminal fluid (semen) provides _______________
for sperm to swim
Internal Fertilization
• After fertilization the embryo is either:
– enclosed in a ____________ and is ejected to
develop outside of females body (oviparous)
• ex: chicken egg
– remains and develops in a special __________
of females body
• ex: human uterus
• Advantages of Internal Fertilization:
– Gametes not _____________ in environment
where they could be destroyed
– Chances of fertilization _____________
– Don’t need __________________________
• they require a huge amount of energy to make!
• Still have ________________ of sperm released to
guarantee fertilization takes place
• Parthenogenisis
– Development of an _______________ into an
adult animal without fusion with sperm
– Ex: many insects including bees, wasps, ants,
also some lizards
• In bees an unfertilized egg will become a male
drone and fertilized eggs become female workers
or queens
Early Embryonic
Development
• Cleavage:
• series of ____________
cell divisions of zygote
• # of cells increases but
growth _____________
• Morula:
• ___________________
• Blastula:
• ___________________
• Gastrulation:
– Cells of blastula _____________________ forming gastrula
– Opening is called the blastopore
• This later becomes the opening to digestive system
• Three cell layers form:
– ______________, _________________ & ______________
Growth & Differentiation of Cells
• Three cell layers of gastrula differentiate into
different tissues of body (___________________)
•
•
•
•
•
•
Ectoderm (outer layer)
_______________________________________
Mesoderm (middle layer)
_______________________________________
Endoderm (inner layer)
_______________________________________
Differentiation
• Differentiation occurs because:
– different sections of DNA called genes
_____________________ in different cells,
controlling what type of cell it will become
– _____________________________ between
adjoining cells can also influence cell type and
development
http://education-portal.com/academy/lesson/overview-of-animal-reproduction-anddevelopment.html
Development & Growth of Embryo
• Development is the process by which the
embryo becomes the organism.
• An embryo needs:
– protection from elements
– a way to get __________________
– regulate temperature
– get rid of it’s __________________
External
Development
• In Water:
– nourishment comes from ______________,
gets oxygen from water, wastes diffuse into
water
– Requires little or no ____________________
• Some animals guard eggs or fan water currents to
provide more oxygen
• On Land
– Need large egg with yolk
(nourishment) protected
by a shell
• A self sustained watery
environment
– ____________________
allows oxygen in and
carbon dioxide out
• Ex: Reptiles, Birds and
Monotremes (Ex: platypus)
Structure of a Typical Egg
• Hard porous shell containing special membranes
• Chorion:
– outermost membrane lining inside of shell
– _____________________ with external environment
• Allantois:
– exchange of ______________ take place
– Metabolic wastes (like uric acid )collect here
– Site for ____________________________
• Amniotic Sac:
– fluid filled sac surrounding embryo
– ________________________ from shock
• Yolk Sac:
– Source of ____________ for embryo
– Has blood vessels to carry food to embryo
Internal Development
• Mammals:
• Internal fertilization
• Embryo develops in ________
or ______________
• When born offspring receives
nourishment from mother from
__________________
• Only _______________ are
produced at a time
• Placental Mammals:
• Embryo becomes implanted in the
_________________
• _____________ that serves as a
organ for exchange of _________,
_______ and ________________
between embryo’s blood and
mothers blood
• Provides embryo with site for:
__________, ____________ and
__________________
• Embryo becomes attached to a
placenta by an
__________________
• No direct mixing of blood
• Non Placental Mammals
– Pouched:
• Marsupials (like Kangaroo)
– Egg Laying:
• _____________ (Echidna), _____________________
– Embryos are born _______________________.
Must complete development in a pouch.
– No _____________________ of young in uterus
– Crawls into pouch, attaches ________________
to complete development
Baby Echidna:
http://www.youtube.com/watch?v=ZXEC1Qx4cJg&safe=active
Kangaroo Giving Birth
http://www.youtube.com/watch?v=2lCKc8tURtc&safe=active
Try These Questions
• What is the function of the placenta?
• Why do fish produce more eggs than birds?
• What advantage is it to have an egg shell on dry
land?
• How do the eggs that develop in water obtain
nourishment and oxygen?
• What happens during gastrulation?