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Conception and Heredity
• Fertilization, or conception,
is the union of an ovum and
a sperm.
• Conception usually occurs in
the upper-third portion of a
Fallopian tube.
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• Fertilization is the joining of an egg cell
and a sperm cell.
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What to Know About Conception
and Heredity
• Heredity is the passing of characteristics from
biological parents to their children and is
determined at conception.
• All body cells, except sperm and ova, contain
23 pairs of chromosomes.
• A chromosome is a threadlike structure that
carries genes.
• A gene is a unit of hereditary material.
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What to Know About Conception
and Heredity
• Chromosomes in men and women
– In both males and females, one pair of
chromosomes is called the sex chromosomes.
• In females, the pair of sex chromosomes is identical
and is called XX. Every ovum produced by a female
contains an X chromosome.
• In males, the pair of sex chromosomes is not
identical and is called XY. Sperm produced by a
male contain either an X chromosome or a Y
chromosome.
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What to Know About Conception
and Heredity
• Chromosomes in men and women
– The sex of a baby is
determined by the sex
chromosome from
the father.
• A fertilized ovum with an
XX set of chromosomes
develops into a female.
• A fertilized ovum with an
XY set of chromosomes
develops into a male.
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What to Know About Conception
and Heredity
• Inherited characteristics
– Inherited characteristics are determined by
genes carried on chromosomes.
– If the maternal and paternal genes for a trait
are different, one will override the other.
• A dominant gene is a gene that overrides the
expression of the other gene.
• A recessive gene is a gene whose expression is
overridden by the other gene.
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What to Know About Conception
and Heredity
• Amniocentesis is a diagnostic procedure in
which a needle is inserted through the uterus to
extract fluid from the amniotic sac.
– The amniotic sac is a pouch of fluid that
surrounds a fetus.
– Cells extracted from the amniotic fluid are
analyzed to determine if any genetic defects
are present.
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What to Know About Conception
and Heredity
• An ultrasound is a diagnostic procedure
in which high high-frequency sound waves
are used to provide an image of the
developing baby.
– Ultrasound can be used
to confirm pregnancy and
the sex of the fetus, and
to help a doctor diagnose
any problems the mother
might be having.
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Pregnancy
• After conception, a fertilized ovum continues to
divide and move through the Fallopian tube.
• The cell divisions form a cluster of cells by the
time they reach the uterus.
• These cells attach to the endometrium, which is
the lining of the uterus.
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Pregnancy
• An embryo is a developing baby through the
second month of growth after conception.
• A fetus is a developing baby from the ninth
week after conception until birth.
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What to Know About Pregnancy
• The outer cells of the embryo and the cells of
the endometrium form the placenta.
• The placenta is an organ that anchors the
embryo to the uterus.
• Other cells form the umbilical cord, which is a
rope-like structure that connects the embryo
to the placenta.
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What to Know About Pregnancy
• How pregnancy is determined
– Absence of a menstrual period may indicate
pregnancy.
– If conception has occurred, a female usually
has other symptoms of pregnancy, such as
fatigue and morning sickness.
– A female who misses a period and also has
other symptoms of pregnancy should have a
pregnancy test.
– Pregnancy usually lasts nine months and is
divided into trimesters or three-month periods.
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What to Know About Pregnancy
• The first trimester
– At the end of the first month, the embryo
has a heartbeat, a two-lobed brain, and a
spinal cord.
– By the end of the second month, the embryo is
recognizable as a human and is called a fetus.
– By the end of the first trimester, the heart has
four chambers.
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8 Weeks
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What to Know About Pregnancy
• The second trimester
– By the end of the fourth month, fingernails,
toenails, eyebrows, and eyelashes
have developed.
– Movement of the fetus can be felt by the
mother, and the fetus can bend its arms and
make a fist.
– During the fifth month, the heartbeat can be
detected by a stethoscope.
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14 Weeks
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18 Weeks
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20 Weeks (5 Months)
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Six Months
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What to Know About Pregnancy
• The third trimester
– Optimum development occurs at about 40
weeks after conception.
– A premature baby is
a baby that is born before
38 weeks of pregnancy.
– A baby born between
38 and 40 weeks of
pregnancy is considered
to be full-term.
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32 Weeks
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40 Weeks
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What to Know About Prenatal Care
• Premature birth or low birth weight may result
when a developing baby does not receive
adequate nutrients.
– Premature birth is the birth of a baby before
it is fully developed—less than 38 weeks
from the time of conception.
– A low birth weight is a
weight at birth that is less
than 5.5 pounds.
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Childbirth
• Labor is the process of childbirth.
• During labor, muscular
contractions of the uterus start,
become more intense, last longer,
and become more frequent.
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Childbirth
• A discharge or gushing of water
from the vagina indicates the
amniotic sac has broken.
• Bloody show, which is the
discharge of the mucous plug
that sealed the cervix during
pregnancy, also may be
experienced.
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What to Know About Childbirth
• Labor is considered to have three distinct stages.
• Stage 1: Dilation of the cervix
– The first stage of labor can last from two
hours to many hours.
– The cervical opening
enlarges eight to ten
centimeters—wide
enough for the baby
to move through.
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What to Know About Childbirth
• Stage 2: Delivery of the baby
– The second stage begins when the cervix is
completely dilated and ends with the delivery
of the baby.
– Crowning is the
appearance of the
baby’s head
during delivery.
– Once the baby has been eased out of the
birth canal and begins to breathe on its own,
the umbilical cord is cut.
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What to Know About Childbirth
• Stage 3: Delivery of the placenta
– The third stage of labor is the expulsion of
the afterbirth.
– The afterbirth is the placenta that is
expelled after delivery.
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What to Know About Childbirth
• When the baby is breathing on its own, the
umbilical cord is clamped and cut off.
• A physician gives the baby an Apgar score,
which is a rating of physical characteristics of
an infant at one and five minutes after birth.
• Characteristics, such as heart rate, color,
respiratory effort, and reaction to sucking,
are scored and used to predict the health
of the baby.
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What to Know About Childbirth
• The postpartum period is the span of time that
begins after the baby is born.
• The breasts secrete a watery substance
believed to provide the baby with immunity to
certain diseases.
• The breasts also secrete a hormone that
stimulates the breasts to secrete milk.
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What to Know About Childbirth
• Multiple births
– Two babies born at the same time are
called twins.
• Identical twins develop from the same ovum
and sperm and have identical chromosomes.
• Fraternal twins develop when two ova are
released from an ovary and are fertilized at the
same time by different sperm.
– Three babies born at the same time are
called triplets. Multiple births of more than
three babies are rare.
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Complications During Pregnancy
and Childbirth
• Ectopic pregnancy,
which can be caused
by tissue scarring
from STDs, is a
pregnancy that occurs
outside of the uterus.
• Ectopic pregnancy can
be fatal to females.
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Complications During Pregnancy
and Childbirth
• Rh incompatibility is a mismatch between the
blood of a pregnant female and the blood of the
developing baby.
• Toxemia of pregnancy is a condition
characterized by a rise in the pregnant female’s
blood pressure, swelling, and leakage of protein
into the urine. Untreated toxemia can be fatal to
females and their developing babies.
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Complications During Pregnancy
and Childbirth
• Miscarriage is the natural ending of a
pregnancy before a baby has developed
enough to survive on its own outside the
mother’s body.
• Cesarean section is a procedure in which a
baby is removed from the mother by making an
incision through the mother’s abdomen and
uterus and removing the baby.
• Stillbirth is a fully developed baby that is
born dead.
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Study Guide
1. Match the following terms and definitions.
___
B chromosome
___
A placenta
___
C postpartum period
___
E Apgar score
___
D crowning
A. an organ that anchors the embryo
to the uterus
B. a threadlike structure that carries
genes
C. the span of time that begins after
the baby is born
D. the appearance of the baby’s head
during delivery
E. a rating of physical characteristics
of an infant at one and five
minutes after birth
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Study Guide
2. Identify the following statements as
true or false.
_______
Fraternal twins have identical chromosomes.
false
_______
A baby born before 38 weeks is classified
true
as premature.
_______
By the end of the third month of pregnancy,
false
the baby’s heartbeat can be detected by
a stethoscope.
_______
The sex of a baby is determined by the sex
false
chromosome of its mother.
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