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 (__________________)

• 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 Simple Organisms

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

• 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

http://www.youtube.com/watch?v=bRKdTAzPBv0&safe=activehttp://www.united-academics.org/magazine/earth-environment/top-ten-weirdest-animal-penises/

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 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-and-development.html

Differentiation

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=activeKangaroo Giving Birthhttp://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?