Transcript Sexual Reproduction

Essential Question: What is sexual
reproduction? What is internal and
external fertilization?
Sexual Reproduction- involves
two partners and results in
offspring that have some genetic
material (DNA) from each parent.
The result is an organism that
may be similar to one or both
parents, but is not identical to
either.
Goals of the Reproductive Process:
• Formation and union
of egg and sperm.
• Development of fetus.
• Birth of the infant
Fertilization:
•
The union (fusion) of a
monoploid sperm
mucleus(n) with a
monoploid egg
nucleus(n).
• Takes place in the
oviduct.
• Male Gamete + Female
Gamete-->Zygote (2n)
Zygote-a fertilized egg
Recombination- process by which the
genes from both parents combine during
fertilization.
Two Types of Fertilization:


External Fertilization
Internal Fertilization
External Fertilization:
•
•
•
•
•
Occurs in aquatic
vertebrates. Exs. fish
and amphibians.
Fertilization outside the
female’s body.
Involves a large
number of eggs.
Nourishment from yolk.
No care by parents.
Internal Fertilization:




Occurs in most
terrestrial vertebrates.
Exs. birds, reptiles, and
mammals.
Fertilization inside the
female’s body (moist
reproductive tract).
Small number of eggs.
Greater chance of
survival.
Essential Question: What are some structures that
terrestrial egg laying organisms have developed to increase
the survival rate of their offspring?
Some adaptations for animals which develop externally on land are:
Shell provides:
• Slow rate of evaporation.
• Porous for gas exchange.
• Protection.
• Prevents bacteria from entering.
Amnion:
• Contains the amniotic fluid.
• Provides a water environment.
• Protects against shock.
• Prevents adhesion of embryo to shell.
Yolk Sac:
• Surrounds yolk.
• contains blood vessels which transport food to embryo.
Allantois:
• Contains blood vessels for oxygen and
carbon dioxide exchange.
• Storage area for metabolic wastes.
Chorion:
• Outer membrane.
Exchange of gases with the environment.
•
Humans are placental
mammals. In fact a few
mammals, such as
marsupials, there is no
placenta. Ex. kangaroo
Marsupials:
•
Pouched mammals.
•
Internal fertilization.
•
Some internal development,
without a placenta.
•
Born at a premature stage
and then completes
development externally
within a pouch.
•
Feed from mammary glands.
• Spiny Anteater and
Duckbill Platypus are
examples of egg
laying mammals.
They lay leathery
eggs (like reptiles),
but offspring feed
from mammary
glands.
Male Reproductive System:
•
•
•
The male
reproductive
system performs
two major
functions:
Production of
sperm cells.
Deposition of
sperm within the
female
reproductive tract.
Structures In the Male Reproductive System:
Testes:
 Located in the scrotum.
 Produces sperm and testosterone.
Scrotum:
 Sac that holds the testes.
 1-2 degrees cooler than body temperature.
Urethra-Tube within the penis that carries urine or sperm
out of the body.
Penis- structural adaptation for internal fertilization.
 Other structures associated with the male productive
system produce the fluids and nutrients that are needed
for the proper function and delivery of the male gametes
to the female reproductive system.
Semen-liquid and sperm cells.
Essential Question: What are the functions of the
structures found in the female reproductive
system?
Female Reproductive
System:
•
The human female
reproductive system is
organized to produce
gametes, to support
internal fertilization
and development, to
exchange materials
through the placenta
and to provide milk to
the offspring.
Structures in the Female System:
Ovaries:
• Paired structures located
in lower portion of the
body cavity.
• Produces eggs (ova) and
the hormones estrogen
and progesterone.
Oviducts(Fallopian
Tubes):
• Open-ended tubes by
the ovaries.
• Site of fertilization.
• Carries egg to uterus.
Uterus:
•
Shaped like an inverted
pear.
•
Composed of three layers.
Endometrium-thin inner layer of
the uterus that sloughs off
during the menstrual cycle.
Cervix:
•
Opening to the uterus.
•
Closed during pregnancy.
Vagina(birth canal):
•
Site where sperm enter and
swim to the oviducts.
•
Passageway for baby.
Essential Question: What is the sequence of
events after the fertilization of the egg?
Fertilization and Development:
• Fertilization usually occurs in
the upper 1/3 o the oviduct. If
the egg is not fertilized within
24 hours after ovulation, it
deteriorates. If fertilization
occurs, cleavage of the zygote
begins in the oviduct, and six
to ten days later the resulting
embryo may be implanted in
the uterine lining. At this stage
of development, the yolk of the
egg has been depleted. But
with implantation, the embryo
can obtain nutrients from the
uterus
Essential Question: What are the stages in the
embryonic development of humans?
Embryonic Development:
•
The zygote contains all the
information necessary for
growth, development, and
eventual reproduction.
The zygote undergoes a
series of rapid mitotic
division called cleavage
Cleavage:
•
Increase in number of
cells, with no increase in
size of cells.
•
Now called an embryo.
Cleavage
Stages of Cleavage:
 Morula
 Blastula
 Gastrula
Morula-solid mass of cells
Blastula-fluid filled mass of cells
Gastrula-embryo forms three layer of cells.
the three layers are:
 endoderm
 mesoderm
 ectoderm
Endoderm:
Inner layer.
Forms the lining of the digestive tract and
respiratory tract, portions of the liver and pancreas.
Placenta:
 Organ responsible for the
passage (by diffusion of
nutrients and oxygen
from the mother’s blood
to the fetus.
 Wastes from the fetus
also diffuse to the mother,
through the placenta.
 Often called the afterbirth.
Umbilical Cord-contains
the blood vessels that
carry material between
the embryo and the
placenta.
Amniotic sac-fluid filled
membrane that protects
the developing fetus.
 During the first few months,
when essential organs are
forming in the embryo, things
can “negatively influence” the
development.
 Exs: Embryo’s own genes
 Inadequate diet
 Use if alcohol, drugs, and
tobacco-->can lead to the
birth of a baby with brain
damage, drug addiction and
or low birth weight.
 Exposure to certain toxins
 Infections Exs. German
measles and AIDS
Birth:
• Occurs after a gestation
period of nine months.
• Strong contractions of the
uterine muscles (labor)
pushes the baby out.
• Expulsion of the placenta
occurs after the delivery
of the baby.
Essential Question: What is the role of hormones in
the menstrual cycle? What are the stages of the
menstrual cycle?
Hormonal Regulation:
►
Hormones control the female and male
reproductive systems, menstrual cycle,
pregnancy, and birth.
Menstrual Cycle:
►
Begins at puberty.
►
Ceases at menopause.
Menopause-permanent ending of the
menstrual cycle.





Consists of four
stages:
Follicle Stage
Ovulation
Corpus Luteum Stage
Menstruation
Follicle stage-Involves the development of an
egg within a follicle.
Follicle:
 Group of cells surrounding the egg.
 Secretion of estrogen that starts the build up
(thickening by blood tissue) of the uterine lining.
Ovulation-release of the egg from the follicle.
Corpus Luteum Stage-secretes progesterone
that continues to build up the uterine lining.
Corpus Luteum-yellow mass of cells that formed
from the ruptured follicle.
Menstruation:
 Periodic shedding of the uterine lining.
 Lasts for approximately 4 days.
 Occurs only when fertilization has not occurred.
Applications of Reproductive
Technology:
Recent discoveries by scientist shave
greatly changed the way we can deal with
many problems involving the reproduction
of humans as well as plants and other
organisms. The knowledge gained has a
variety of agricultural, ecological and
medical applications.
Agriculture:
Production of plants resistant to insects,
weed killers, and frost.
New improved plants can then be cloned.
Cloning:
 Technique that results in the
same type of offspring as
asexual reproduction.
 Involves inserting a nucleus
from a parent organism into an
egg cell that has had the
nucleus removed.
 100% of the genetic
information is from a single
parent.
 Accomplished with plants,
sheep, pigs, and monkeys.
Cuttings

 Using artificial insemination,
scientists can produce 100’s of
offspring. Ex. cattle
 Also freeze sperm or fertilized
egg and transport them.
Ecology:
Increases populations of endangered
species. Embryos from endangered
species have been transplanted into
related species, who later gave birth
without any ill results.
• Hormones that regulate reproduction in
insects are being used as an alternative to
pesticides(chemicals that kill pests).
Medicine:
• Hormonal therapy used to
adjust their hormones to
normal levels for infertile
woman.
In Vitro fertilization-removal of
several eggs that are then
fertilized with sperm and
implanted in a woman’s uterus.
• Use of ultrasound and
miniature video camera to
detect abnormalities in
reproductive structures or in
the developing fetus.
Amniocentesis-removal of
amniotic fluid (containing fetal
cells) to analyze for
chromosome abnormalities
and for biochemical
deficiencies.