Conjoined twins originate from a single fertilized egg that begins to split into identical twins early in development but fails to completely separate, leaving the twins joined in some part of their body. The most famous historical case was Chang and Eng Bunker, born in 1811 in Siam, who were joined at the chest and shared a liver. Despite initial beliefs they were an ill omen, they went on to marry sisters and have over 20 children together before dying within hours of each other in 1874. Modern medical technology now allows many but not all conjoined twins to be separated, with an overall low survival rate of between 5-25% for conjoined twins.

2. The passing on of certain
inherited characteristics from
one generation to another.

3.  Hair
 Eyes
 Height
 Intelligence
 Talents
 Dimples

4.  Defective gene from one or both parents
1. Downs Syndrome
2. Hemophilia
3. Muscular Dystrophy
4. Sickle Cell Anemia
5. Cleft Palate
6. Cystic Fibrosis
7. Spina bifida

5.  46 chromosomes carry thousands
of genes.
 Contain all the characteristics a
person will have.

6.  Males have XY chromosomes
 Females have XX chromosomes
 Egg and Sperm cells have only 23
chromosomes
 All eggs are X, sperm can be X or Y
 Sperm cell from father determines sex
of baby

8.  Chromosome: Threadlike particles
in nucleus of cell which carries
hereditary factors.
 Genes: Part of the chromosome
that determines all inherited
characteristics

9.  Dominant: Stronger gene that
determines appearance of a trait.
 Recessive: Weaker gene; will not
appear when paired with a
dominant gene

10. Dominant Gene Recessive Gene
eye coloring brown eyes grey, green, hazel, blue eyes
vision farsightedness normal vision
normal vision nearsightedness
normal vision night blindness
normal vision color blindness*
hair dark hair blonde, light, red hair
non-red hair red hair
curly hair straight hair
full head of hair baldness*
widow's peak normal hairline
facial features dimples no dimples
unattached earlobes attached earlobes
freckles no freckles
broad lips thin lips
appendages extra digits normal number
fused digits normal digits
short digits normal digits
fingers lack 1 joint normal joints
limb dwarfing normal proportion
clubbed thumb normal thumb
double-jointedness normal joints
other immunity to poison ivy susceptibility to poison ivy
normal pigmented skin albinism
normal blood clotting hemophilia*
normal hearing congenital deafness
normal hearing and speaking deaf mutism
normal- no PKU phenylketonuria (PKU)
* sex-linked
characteristic

13.  A. Identical twins: 1 egg + 1 sperm -- splits
into two children, must be the same sex.
 B. Fraternal Twins: 2 eggs + 2 sperm –both
fertilized; can be same sex or one of each.
 C. Siamese Twins: Conjoined twins – 1 egg
+ 1 sperm split, however the split does not
completely occur.

14.  Identical Twins:
 One fertilized egg splits in half, each half develops into
a separate embryo.
 Happens soon after fertilization
 Offspring share DNA, they are the same sex
 ONE EGG, ONE SPERM, ONE PLACENTA
 Fraternal Twins:
 Two eggs are released at same time, each fertilized by
different sperm.
 No more alike genetically than any siblings
 TWO EGGS, TWO SPERM, TWO PLACENTAS

16.  ONE EGG, ONE SPERM
 EGG STARTS TO SPLIT AS IN IDENTICAL TWINS, BUT
DOESN’T COMPLETE THE SPLIT.
 EMBYROS WILL DEVELOP ATTACHED
 can be extremely traumatic
 approximately 40-60% of these births are delivered
stillborn with 35% surviving just one day.
 overall survival rate between 5-25%
 historical records over the past 500 years detail
about 600 surviving sets of conjoined twins with
more than 70% of those surviving pairs resulting in
female twins.

19.  There is an extremely rare form of identical twins that occurs perhaps in
one out of every 75,000 to 100,000 births or 1 in 200 deliveries of identical
twins, that of conjoined twins. Conjoined twins originate from a single
fertilized egg so they are always identical and same-sex twins. The
developing embryo starts to split into identical twins within the first two
weeks after conception but then stops before completion, leaving a
partially separated egg which continues to mature into a conjoined
fetus.
 The most famous set of conjoined twins were Chang and Eng, the men
who originated the term "Siamese Twins". Eng and Chang were born in
Siam (modern day Thailand) on May 11, 1811 to a Chinese father and half-
Chinese, half-Malay mother. Thanks to their heritage, while growing up
in Siam the boys were known as "The Chinese Twins". Despite the fact
that their birth was initially believed to be an omen of the end of the
world, they brought celebrity to their small village. Their mother refused
to allow doctors to attempt to separate the boys, fearing that to do so
would result in the death of one or both. Instead she taught them to
stretch the tissue that joined them so that they could stand side-by-side
rather than always face-to-face.

20.  Chang and Eng began to date Adelaide and Sarah Ann Yates, two
of nine daughters of local farmer and part-time clergyman,
David Yates. The townspeople disapproved, so Chang and Eng
scheduled a separation surgery in Philadelphia. Their fiancées
found out and quickly stopped the proceeding, and in April, 1843,
Chang was married to Adelaide and Eng to Sarah Ann in a double
wedding.
 During the course of their marriages, Eng fathered six boys and
five girls; Chang seven girls and three boys. All were normal
except for a son and daughter of Chang's who were deaf mutes.
 In January, 1874, Chang Bunker died after a severe case of
bronchitis, possibly from a cerebral clot. Eng died shortly
thereafter.
 After their deaths it was determined they could have been
successfully separated, a medical option that was never offered to
Eng and Chang during their lives.

21. Although Eng and Chang's fame helped coin the phrase 'Siamese
Twins', they were not the first pair of conjoined twins recorded in
medical annals as there were probably about 100 such pairs
known by the time of their 1811 births, a fact which helped the
King of Siam reverse an early death sentence on the brothers. In
fact, conjoined twins were recorded as early as 945 in Armenia and
the first pair of successfully separated twins took place in 1689 by
German physician G. König.
The birth of two connected babies can be extremely traumatic
and approximately 40-60% of these births are delivered stillborn
with 35% surviving just one day. The overall survival rate of
conjoined twins is somewhere between 5-25% and historical
records over the past 500 years detail about 600 surviving sets of
conjoined twins with more than 70% of those surviving pairs
resulting in female twins.

23.  Infertility: Problems of conception or
implantation have occurred
 Fertility Analysis: What options does a
couple have

24. a. Fertility Drugs
b. Artificial Insemination – Sperm is injected into woman's
uterus.
c. IVF (Invitro-Fertilization) – Sperm and egg are fertilized
outside of body and then placed in the uterus – Test tube
baby – very expensive with only a 80-90% chance of
pregnancy. Variation: Ovum transfer
d. Surrogate Mother: Carries fertilized egg through IVF for
couple or may be artificially insemination by father’s
sperm
e. Adoption

25.  An abnormality that affects the
structure or function of the body.
 Hereditary & Environmental

26.  Any pregnancy that ends due to natural
causes before the embryo/fetus could
possibly survive on its own.
 20% of pregnancies end in miscarriage
 After 20 weeks, known as a stillbirth

27.  Anything affecting the fetus by what
the mother has done while pregnant;
poor nutrition, alcohol, drugs, x-rays
etc.

28.  Downs Syndrome: 21st chromosome
pair has 3 chromosomes instead of
usual 2

29.  Mother and baby have different blood types;
 Example: Mother RH -, Father RH +, =
Baby RH+
 Mother will have an RH different from her
own after labor and delivery and her body
will begin to make antibodies to fight of this
“intruder”
 Next baby is rejected by mothers immune
system.

30.  Informs parents in advance the odds
that their children will have a certain
disease.
 Parents suspect a problem from:
1. Medical/Family History
2. Physical Exam
3. Lab Tests

31.  Amniocentesis: Needle inserted through belly
button withdraws amniotic fluid; Recommended
for women over 35.
 Ultra Sound – Sound waves make an image to
insure fetus is developing normally.
 Chorionic Villi Sampling: Catheter goes through
vagina into uterus for sample of tissue from
membrane encasing fetus; Can find out results
much sooner that amniocentesis.

32.  Alcohol – FAS, Women should not have any amount
 Over the Counter Medications: Aspirin, Ibuprofen etc.
May cause problems for baby
 Caffeine: Coffee, tea, sodas, chocolate;
 Tobacco: Premature & Low birth weight
 Illegal Drugs: Serious addictions and brain damage
 X-rays: Radiation; make sure to tell Doctor or Tech.
 Rubella or German Measles: Vaccine now
 STD’s : Birth defects or blindness etc.
 Other Infections: Should always discuss with doctor.

33.  Addiction passed on to fetus
 Prematurity and low birth weight
 Withdrawal – painful and may even
cause death
 Birth defects
 Learning Disorders