Sexual Reproduction
Why Reproduce?
•
Survival of the species
Species - a group of closely related organisms that can produce fertile offspring.
•
Needed to transfer genetic
Sexual Reproduction
• Sexual reproduction-
– two parents
– Offspring have ½ of their
genetic material from each parent.
– Offspring NOT identical to either
Sexual Reproduction
• How do we get HALF
of the genetic
information from each parent?
Meiosis: “Double Cell Division”
•
Involves
ONE
replication and
TWO
divisions.
•
Prior to the TWO cell divisions
the DNA replicates once
Crossing Over
Crossing Over: When homologous chromosomes exchange some genetic information during meiosis
Meiosis I: First Division
• Prophase I
– Homologous pairs of chromosomes come
together, form tetrads ( four Chromotids)
–
crossing over occurs !!!!!!!
Meiosis I: First Division
• Metaphase I
Meiosis I: First Division
• Anaphase I
– Disjunction- the tetrads are separated and double-stranded chromosomes are
pulled toward the poles.
– The Homologous pairs separate
– IDEPENDENT ASSORTMENT - Leads to variation
• Telophase I
Meiosis II: Second
Division
Metaphase II
• As the cell enters
• These four
The Results….
• Meiosis I : 2 haploid (n)
daughter cells, with ½ the
number of chromosomes as the original cell.
• Meiosis II : 4 haploid (n)
Meiosis – Animation ON WEBSITE
Fig. 13-7-3
Interphase
Homologous pair of chromosomes in diploid parent cell
Chromosomes replicate
Homologous pair of replicated chromosomes
Sister
chromatids Diploid cell with replicated chromosomes
Meiosis I
Homologous chromosomes separate
1
Haploid cells with
replicated chromosomes
Meiosis II
2 Sister chromatids separate
Comparing Mitosis &
Meiosis
Mitosis Meiosis
Associated with growth and asexual reproduction
Associated with sexual reproduction - making
sperm and eggs (occurs in testes and ovaries ONLY!) Daughter cells are identical
to the parent
Daughter cells have ½ the # of chromosomes of parent cell
One Replication, One Division
One Replication, TWO Divisions
Two daughter cells are produced
Gametogenesis
•
Formation of
gametes
(sperm and
egg)
•
Gametes are made in the
gonads
(testes and ovaries)
•
Involves
meiosis – cells produced
Meiosis I: Reduction Division
• DIPLOID cell in an ovary or testes is divided into
two HAPLOID cells.
46
Meiosis II:
• Those 2 HAPLOID cells each divide again
resulting in FOUR gametes that are all genetically different.
23 23
Some Sexual Reproduction
Vocabulary
•
Gametes
: Specialized sex cells
(sperm & eggs)
•
Fertilization:
Fusion of the nuclei
of sperm and egg
More Vocabulary
• Diploid: Number of chromosomes in “body
cells” of an organism – 2n (human = 46)
• Haploid: Number of chromosomes in an
More Vocabulary
• Body cells: Somatic Cells -(skin cells, nerve
cells, liver cells) of an organism contain a diploid number of chromosomes (2n = 46)
• Gamete cells (sperm and eggs) contain a
Disjunction
Disjunction
When fibers pull homologous chromosomes toward poles.
Nondisjunction
Nondisjunction
When fibers FAIL to pull
homologous chromosomes toward poles.
This can result in chromosome abnormalities
Functions of the Male Reproductive System
1. Produce Sperm (male sex cell or gamete)
2. Deposits sperm in female for fertilization.
3. Produces the hormone called testosterone.
• Testosterone produces the secondary sex
The Male Reproductive System
Structures &
Function
1. Testes- produce the sperm and testosterone
2. Epididymus- sperm fully mature and are stored here.
3. Vas deferens- carries sperm from epididymis to urethra.
4. Urethra- tube leading outside body through penis. 5. Scrotum- External sac that holds testes. Lower
temperature allows sperm to mature.
Hormones
• FSH : Stimulates Spermatogenesis
• LH: Stimulates production of testosterone by
the testis ( Leydig Cells )
• Testosterone: Secondary Sex Characteristics
COMPONENT OF SEMEN
• 1. Seminal fluid - Seminal vesicles and prostate
gland secrete a fluid for sperm to travel through and nourishes the sperm.
• 2.
FYI: About 200 to 600 million sperm, are released in an average ejaculation. This increases the
chances of fertilization.
SPERM
• 1. Produced in the testes
by meiosis.
• 2. Haploid- sperm cells
contain 23
chromosomes (n #).
• 3. A sperm cell consists
Acrosome
• An organelle that develops over the anterior half
of the head the sperm
• It is a cap-like structure derived from the Golgi
apparatus.
• Contains digestive enzymes that break down the
FUNCTIONS OF THE FEMALE
REPRODUCTIVE SYSTEM
• Produces eggs (female sex cell or gamete)
Ovulation- one egg is released per month
• Prepares the female’s body to nourish a
developing embryo
• Female secondary sex characteristics are
regulated by estrogen & progesterone.
Main Structures of the
Female Reproductive System
• 1. Ovaries- Paired structures
that produce eggs & hormones.
• 2. Fallopian tubes ( Oviduct) -
Carries egg to uterus. Where egg is fertilized.
• 3. Uterus- Development takes
place.
• 4. Cervix- Lower Uterus
• 5. Vagina- Where sperm is
Ectopic Pregnancy
Fibroids
Sexually Transmitted Diseases
• Chlamydia and Gonorrhea can cause Pelvic
Inflammatory Disease
• Syphilis: Final stage can reach nervous
system
Egg Development
• Eggs are produced within
the ovaries of females.
• Females are born with
over 400,000 eggs.
• Only about 400 of these
eggs will mature and be released.
• Ovulation- mature egg is
The Reproductive Cycles of Females
• In females, the secretion of hormones and the
reproductive events they regulate are CYCLIC
• Prior to ovulation, the endometrium thickens with
blood vessels in preparation for embryo implantation
• If an embryo does not implant in the endometrium,
the endometrium is shed in a process called
Stages of the Menstrual Cycle
• Follicle Stage - egg matures inside follicle,
estrogen is released to start thickening uterine lining.
• Ovulation Stage - Release of egg from follicle
• Luteal Stage - Corpus luteum forms from leftover
follicle after ovulation; progesterone gets released to further build-up uterine lining
• Menstruation - shedding of uterine lining – occurs
Fertilization
• Formation of zygote. • Occurs in upper
Development of the
Zygote
Zygote divides by MITOSIS known as CLEAVAGE!
Blastula :hollow ball of single layered cells that develops
Fig. 46-15
Ovary
Uterus
Endometrium (a) From ovulation to implantation
(b) Implantation of blastocyst
Cleavage Fertilization Ovulation Cleavage continues The blastocyst implants Trophoblast Inner cell mass
Formation of the Gastrula
The infolding of the Blastula is called Gastrulation
• Animation
Differentiation
The 3 layers of the Gastrula develop into various tissues and organs.
– Ectoderm: Nervous system, Skeletal & Skin – Mesoderm : Organ systems such as
muscular, circulatory, reproductive, and excretory
– Endoderm : lining of the digestive tract
and respiratory tract. Liver and pancreas
The unspecialized (stem cells) cells become
If body cells have the same DNA –Why do
they look different and have different
functions?
BECAUSE ONLY PART OF THE DNA IN EACH CELL IS EXPRESSED or USED.
Adaptations for Sexual Development
• Fertilization – The fusion of the haploid
sperm cell nucleus (n) with a haploid egg cell nucleus (n) to create a diploid zygote (2n).
• Two Types of Fertilization:
Internal vs. External
Fertilization
• External Fertilization:
– Sperm and egg fuse
outside body of organism
– Large numbers of
sperm and eggs are produced to ensure fertilization
– Used by aquatic
organisms (fish & frogs)
• Internal Fertilization:
– Sperm and egg fuse
inside reproductive tract of the female
– Occurs in most
Adaptations for Development
-Nourishment -Oxygen -Temperature -Remove Waste -Protection• Two Places Development Occurs:
- External Development - Internal Development
External vs. Internal
Development
•
External Development
:– Water : (fish and frogs) Offspring develop
outside mother’s body in water – little or no care by parent – many eggs are eaten or destroyed
– Land : (birds and reptiles) – fertilized egg
Internal Development
•
Embryos develop within uterus
•
Offspring are well protected & a
high percentage survive
Fig. 46-15
Ovary
Uterus
Endometrium (a) From ovulation to implantation
(b) Implantation of blastocyst
Cleavage Fertilization Ovulation Cleavage continues The blastocyst implants Trophoblast Inner cell mass
Internal Development
Placenta
• Site of diffusion; materials are exchanged here
between mother and child. Ex. glucose, water, CO2, O2
*****Through the BLOOD
• During its first 2 to 4 weeks, the embryo obtains
nutrients directly from the endometrium
• A layer of the blastocyst, called the trophoblast,
mingles with the endometrium and eventually forms the placenta
• Blood from the embryo travels to the placenta
through arteries of the umbilical cord and returns via the umbilical vein
Placenta
Things that cross the Placenta
• Drugs – Birth Defects, addicted babies, stillborns • Alcohol- Fetal Alcohol Syndrome, stillborns
• Cigarette smoke – Slow growth, stillborns • Viruses - Blindness, Mental Retardation,
stillborns
• Food: Good nutrition is very important while
Drugs can cross the placenta and cause birth defects and harm the fetus
Alcohol can cross the placenta and cause birth defects and harm the fetus
Viruses can cross the placenta and cause birth defects and harm the fetus
Examples:
Chicken Pox
Herpes
Internal Development
Amniotic Sac
• Nourishing and protecting sac containing liquid (Amniotic Fluid)
• Grows and begins to fill, mainly with water, around
two weeks after fertilization.
• After 10 weeks it contains proteins, carbohydrates,
lipids which aid in the growth of the fetus.
• In the late stages of gestation much of the amniotic
Fig. 46-17
• The first trimester ( 1- 12 weeks ) is the main
period of organogenesis : development of the body organs
• All the major structures are present by 8 weeks,
and the embryo is now called a fetus
• Changes occur in the mother
– Growth of the placenta
– Cessation of ovulation and the menstrual cycle
– Breast enlargement
Second Trimester
• During the second trimester (12-27)
– The fetus grows and is very active
– The mother may feel fetal movements
– The uterus grows enough for the pregnancy to
Fig. 46-17c
Third Trimester
• During the third trimester (28-40), the fetus grows
and fills the space within the embryonic membranes
• A complex interplay of local regulators and
Fig. 46-18
Estradiol Oxytocin
from ovaries
Induces oxytocin receptors on uterus
Fig. 46-19-1
Placenta
Umbilical cord
Uterus
Cervix
Fig. 46-19-2
Expulsion: delivery of the infant
Fig. 46-19-3
Delivery of the placenta
Uterus
Placenta
(detaching)
Umbilical
cord
Detecting Disorders During
Pregnancy
• Amniocentesis and chorionic villus sampling are
invasive techniques in which amniotic fluid or fetal cells are obtained for genetic analysis
• Noninvasive procedures usually use ultrasound
imaging to detect fetal condition
• Genetic testing of the fetus poses ethical questions
Artificial Insemination
–
Used to treat
infertility
–
Sperm are injected
into female with
probe
In Vitro Fertilization
•
Sperm and egg are
joined in lab and
then zygote is
implanted
in
Surrogate Pregnancy
•
In vitro fertilization
is performed
•
Embryo is implanted in woman who has
no genetic attachment
•
Woman will house embryo and deliver
Sex Selection
• DNA of sperm and egg
are screened for X and Y chromosomes for desired combination.
Sperm carry X or Y Eggs carry only X
• Sorting Technique or
genetically test for X or Y
• It’s a Girl XX
• It’s a Boy XY
Monozygotic Twins
(Identical Twins)
• One egg is fertilized by one sperm
• Embryo splits into two during the early stages of
development
• Have identical genes and must be of the same sex
Dizygotic Twins
(Fraternal Twins)
• Two eggs are ovulated and each is fertilized by a sperm cell
• No more genetically similar than any other sibling in the
family (can be same/different sexes)
• Maternal age, use of assisted reproductive technologies are
factors
• Incidence (6.7/1000 births in Japan to 40/1000 births in