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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.


• Fertilization is the joining of an egg cell and a sperm cell.


• Heredity is the passing of characteristics from biological parents to their children and is determined at conception.

What to Know About Conception and Heredity

• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


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.


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.


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.



• 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.



• 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.


8 Weeks



• 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.


14 Weeks


18 Weeks


20 Weeks (5 Months)


Six Months



• 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.


32 Weeks


40 Weeks


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.


Childbirth

• Labor is the process of childbirth.

• During labor, muscular contractions of the uterus start, become more intense, last longer, and become more frequent.


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.


What to Know About Childbirth

• Labor is considered to have three distinct stages.

– 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.

• Stage 1: Dilation of the cervix



• 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.



• 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.



• 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.



• 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.



• 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.


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.


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.


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.


Study Guide

1. Match the following terms and definitions.___ chromosome

___ placenta

___ postpartum period

___ Apgar score

___ 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

B

A

C

E

D


Study Guide

2. Identify the following statements as true or false.

_______ Fraternal twins have identical chromosomes.

_______ A baby born before 38 weeks is classified as premature.

_______ By the end of the third month of pregnancy,

the baby’s heartbeat can be detected by a stethoscope.

_______ The sex of a baby is determined by the sex

chromosome of its mother.

false

true

false

false

End of the Lesson

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