Download Lesson 21

What You’ll Learn
1. Explain how a baby is conceived and how the
baby’s sex and inherited traits are determined.
2. Explain how pregnancy
is determined.
3. Explain why prenatal
care is important.
4. Describe the three
stages of labor.
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Key Terms
• fertilization
• labor
• chromosome
• afterbirth
• gene
• amniocentesis
• ultrasound
• embryo
• placenta
• fetal alcohol
syndrome (FAS)
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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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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
• Genes
– All chromosomes carry genes that contain
hereditary material.
– Sex-linked characteristics are hereditary
characteristics, such as color vision or blood
clotting, that are transmitted on the sex
chromosomes.
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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
• Genetic counseling
– Genetic counseling is a process in which
a trained professional interprets medical
information concerning genetics to
prospective parents.
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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
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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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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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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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Prenatal Care
• Prenatal care is the care that is
given to the mother and baby
before birth.
• Prenatal care includes medical
examinations, proper nutrition,
childbirth and child-care
education, and avoidance of
risk behaviors.
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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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What to Know About Prenatal Care
• A pregnant female needs to check with her
physician before she takes any prescriptions
or over-the-counter drugs.
• A female should not drink alcohol during
pregnancy.
• Fetal alcohol syndrome, or FAS, is the
presence of severe birth defects in babies born
to mothers who drink alcohol during pregnancy.
• Smoking and breathing smoke from tobacco
products increase the risk of complications,
miscarriage, and stillbirth during pregnancy.
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What to Know About Prenatal Care
• A miscarriage is the natural ending of a
pregnancy before a baby is developed enough
to survive on its own outside the mother’s body.
• A stillbirth is the birth of a dead fetus.
• Babies born to mothers who use drugs can be
born prematurely, have low birth weight, and can
be addicted to drugs.
• Caffeine may be linked to birth defects.
• Folic acid is one nutrient known to prevent
birth defects.
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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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What to Know About Childbirth
• Childbirth classes
– Childbirth classes are available from
hospitals, health centers, and other
organizations to prepare prospective parents
for the birth of their baby.
– Special exercise classes also are offered for
pregnant females to help them stay fit during
pregnancy and prepare for childbirth.
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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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Study Guide
3. Describe how the sex of a baby is determined.
Every ovum produced by a female contains an
X chromosome. Sperm produced by a male
contains either an X chromosome or a Y
chromosome. When the sperm fertilize the ovum
to create a complete set of 46 chromosomes,
the combination of the sex chromosomes will
either be XX or XY. An XX combination will result
in a female baby. An XY combination will result in
a male baby.
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