1. Fertilization and Development
Regents Biology

2. OBJECTIVES
Upon completion of this unit students will be able to:
1. Understand that the fusion of haploid gametes restores the diploid number of a species.
2. Briefly describe the processes of fertilization and implantation.
3. Identify the sites of fertilization and implantation in humans.
4. Briefly describe the process of in vitro fertilization.
5. Compare and contrast the production and genetic composition of fraternal and identical
twins.
6. Describe the stages of development of a zygote from start to finish.
7. Describe what happens to a woman before, during and after she undergoes the
birthing process.
8. Differentiate internal and external development
KEY WORDS
1.   amnion
2.   blastula
3.   differentiation
4.   fraternal twins
5.   gastrula
6.   gastrulation
7.   gestation
8.   identical twins
9.   implantation
10.   morula
11.   placenta
12.   zygote

3. PENIS  VAGINA  CERVIX UTERUS ZYGOTE I. Fertilization
Path of sperm from the male to the female:
  PENIS
  
  VAGINA
   
CERVIX
  UTERUS
  OVIDUCT
 If an egg is passing down the OVIDUCT, fertilization occurs
The egg secretes a chemical that ATTRACTS the sperm
After fertilization, membranes around the egg change to prevent PENETRATION by other sperm
Sperm nuclei and egg nuclei UNITE, forming a DIPLOID zygote
ZYGOTE

4. II. Implantation and Development
After fertilization, the zygote undergoes CLEAVAGE (blastula)
The zygote moves down the OVIDUCT to the UTERUS
The embryo attaches to the UTERINE LINING (implantation)
After implantation, GASTRULATION occurs
(fertilization) zygote  EMBRYO  FETUS (8 weeks); until the end of pregnancy, the term fetus is used
During pregnancy, PROGESTERONE is kept at high levels to keep the uterine lining THICK

5. III. Embryonic Development
A. Cleavage
A zygote divides by MITOSIS
Cells DO NOT GROW during cleavage
Cells DIVIDE and actually get SMALLER (remember that an oocyte (or egg cell) is bigger than a normal cell)
OOCYTE (egg cell)

6. Flow chart of embryonic development: MORULA  BLASTULA  GASTRULA

7. B. Gastrulation
Cell layers form in the developing EMBRYO; these are also called GERM LAYERS
These three layers give rise to TISSUES AND ORGANS

8. ECTODERM
MESODERM
ENDODERM
NERVOUS SYSTEM
LINING OF MOUTH, NOSTRILS, ANUS
EPIDERMIS, HAIR, NAILS
BONES AND MUSCLES
BLOOD AND BLOOD VESSELS
REPRODUCTIVE AND EXCRETORY SYSTEMS
DERMIS
DIGESTIVE TRACT
RESPIRATION
LIVER, PANCREAS
GLANDS
BLADDER

9. During GASTRULATION, the cells begin to GROW before dividing
C. Growth and Differentiation
Flow chart of growth and differentiation:
  ZYGOTE
   
EMBRYO
  
  MORULA
BLASTULA 
GASTRULA
FETUS
PART OF EMBRYONIC DEVELOPMENT

10. BLASTULA 8-CELL EMBRYO (GASTRULATION)

11. IV. Control of Development
The nucleus contains DNA and all cells have the same DNA
DNA controls all CELL PROCESSES
Q: If DNA controls cell activities and all cells of an organism contain the same DNA, how are so many different cells made?
A: Different sections of DNA are TURNED ON AND OFF to make different cells
Control of development involves an interaction between CYTOPLASM and DNA
The path of development is determined by the GASTRULA stage

12. FETUS – 8 weeks
FETUS – 6 months
FETUS – 7 months
FETUS – 8 months

13. V. Nourishment
Before implantation, the embryo gets food from YOLK
After implantation, the embryo gets food from the PLACENTA
The placenta is the CHORIONIC VILLI and UTERINE LINING
NOTE: The BLOOD of Mom and fetus DO NOT MIX!!
Nutrients get from Mom to the fetus by DIFFUSION through the umbilical cord
The AMNION contains AMNIOTIC FLUID to protect the fetus

15. VI. Birth
Humans have a gestation period of 9 MONTHS
Labor consists of CONTRACTIONS; the cervix dilates from 1-2 cm to cm
“Water breaks” = AMNIOTIC MEMBRANE BREAKS; FLUID COMES OUT (EASE OF PASSAGE)
Normally, babies come out HEAD FIRST
Afterbirth = PLACENTA + AMNION ARE EXPELLED
PROLACTIN is a hormone for stimulating mammary glands

17. Multiple Births
Fraternal twins = 2 EGGS ARE FERTILIZED BY TWO SEPARATE SPERM RESULTING IN NON-IDENTICAL TWINS
Identical twins = ONE EGG IS FERTILIZED BY ONE SPERM RESULTING IN IDENTICAL TWINS

18. FERTILIZED EGG SPLITTING =
FRATERNAL TWINS
FERTILIZED EGG SPLITTING =
 IDENTICAL TWINS
IDENTICAL TWINS

20. VIII. External and Internal Development
An embryo needs the following to survive: NOURISHMENT, PROPER TEMPERATURE, OXYGEN, PROTECTION, WAY OF GETTING RID OF WASTE
A. External Development in Water
Occurs in AQUATIC animals
The nourishment comes from the EGG YOLK
The environment provides the right TEMPERATURE and PROTECTION
OXYGEN diffuses in
WASTES diffuse out
Most parents do not provide care, so there is a LARGE NUMBER OF EGGS PRODUCED AND FERTILIZED

21. B. External Development on Land
This occurs in BIRDS, SOME REPTILES AND MAMMALS
Involves an EGG WITH A HARD SHELL
The shell of the egg is POROUS (O2 can enter and CO2 can exit by diffusion)
Eggs with shells have a better chance at SURVIVAL because they are PROTECTED
BIRDS: Parents CARE FOR YOUNG
REPTILES: Parents ABANDON EGGS (SO MORE EGGS ARE PRODUCED)

22. C. Internal Development
SHARKS AND SOME REPTILES – Have INTERNAL development and get nourishment from YOLK
MAMMALS – Have INTERNAL development and get nourishment from MOTHER
Embryos develop in the UTERUS
Milk comes from the MAMMARY GLANDS
High percent of SURVIVAL
A FEW amount of eggs are produced

23. Placental Mammals
The nutrients, oxygen, and waste diffuse between the MOTHER’S and the FETUS’ circulatory system by the PLACENTA
The placenta is attached to the wall of the UTERUS
The embryo is attached to the placenta by the UMBILICAL CORD

24. Non-placental Mammals A. Egg-Laying There is no PLACENTA involved
Non-placental mammals lay their eggs and then feed their young
Example : DUCK-BILLED PLATYPUS

25. This is exclusive to the MARSUPIALS
B. Pouched
This is exclusive to the MARSUPIALS
Nourishment occurs from EGG YOLK to OFFSPRING
Marsupials are born very immature and then CRAWLS into Mom’s pouch for complete development
Example: KANGAROO