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Chapter 2
The Start of Life: Genetics and Prenatal Development (part two)

The Start of LifeÖ
Genetics & Prenatal Developmental Development

Fertilization: The Moment of Conception

The joining of the sperm and ovum to create the single-celled zygote that develops into a baby.

Females are born with 400,000+ ova, which mature at puberty.

Males produce sperm with a much shorter lifespan--several hundred million sperm per day in adult male.

Prenatal Growth & Change

Developmentalists divide the prenatal period into three phases: the germinal, embryonic, and fetal stages.

The 3 Phases of the Prenatal Period:


The first and shortest stage of prenatal development

Takes place during the first two weeks following conception.

Characterized by methodical cell division and the attachment of the organism (blastocyst) to the wall of the uterus.

The baby is called a zygote at this stage.

The 3 Phases of the Prenatal Period, continued


the period from two to eight weeks following fertilization during which significant growth occurs in the major organs and body systems.

At this point the child is called an embryo.

The developing child is now composed of three layers:

the ectoderm (the outer layer forming the skin, hair, teeth, sense organs, the brain and spinal cord).

the endoderm (the inner layer producing the digestive system, liver, pancreas, and respiratory system).

the mesoderm (sandwiched between the inner and outer layers and forms the muscles, bones, blood, and circulatory system).

The 3 Phases of the Prenatal Period, continued

3) The FETAL STAGE begins about eight weeks after conception and continues until birth.

The developing child from eight weeks after conception until birth is called a FETUS.

The fetus dramatically increases in size and weight.

Organs become more differentiated and operational.

By three months the fetus swallows and urinates.

By four months the mother will be able to feel her fetus move



About 15 % of couples suffer from infertility (inability to conceive after 12 to 18 months of trying)

There are several causes:

Parental age

Previous use of birth control pills, illicit drugs or cigarettes, STDs, or drugs during pregnancy by womanís mother.

Men with an abnormally low sperm count.

Most common cause is failure to release an egg through ovulation (hormonal imbalance, structural damage, stress).


Several Alternate Routes to Pregnancy

-- ARTIFICIAL INSEMINATION (fertilization that occurs after a man's sperm is placed directly into a woman's vagina by a physician).

-- IN VITRO FERTILIZATION (IVF) (a procedure in which a woman's ova are removed from her ovaries, and a man's sperm are used to fertilize the ova in a laboratory).

-- SURROGATE MOTHER, a woman who agrees to carry the child to term, may be used in cases where the mother is unable to conceive.

Ethical Issues Related to Infertility Treatments

Some surrogate mothers have refused to give up the child

Is it ethical for parents to engage in sex selection techniques now being use?

Is there a problem with eventually choosing eye or hair color or trying to "fertilize" for intelligence?

Do children conceived with reproductive technologies fare as well as naturally conceived children?

Research suggests there appears to be no difference in psychological adjustment.

Evidence suggests that the quality of parenting in families who have used artificial means to conception may even be superior to naturally conceived children.

The psychological adjustment of children conceived artificially is no different than that of children conceived using natural techniques.

Miscarriage and Abortion

Miscarriage (spontaneous abortion) - embryo detaches from wall of uterus and is expelled.

Fifteen to 20 percent of all pregnancies end in miscarriage.

Many occur so early that mother may not have even been aware of pregnancy or miscarriage.

Typically caused by genetic abnormalities.

Abortion - voluntary termination of pregnancy

Involves complex physical, psychological, legal and ethical issues.

Woman may feel regret, guilt, relief in the short term but most women donít have serious emotional problems long-term.

Threats to Prenatal Development

Certain aspects of mothers' and fathers' behavior, both before and after conception, can produce lifelong consequences for the child.

TERATOGENS are environmental agents such as a virus, chemical, or other factor that produces a birth defect.

At some phases of prenatal development, a teratogen may have minimal impact; at other periods, consequences can be severe.

Other threats to prenatal development

Mother's diet clearly plays an important role in bolstering the development of the fetus.

Motherís age - Research shows that mothers over 30 and adolescent mothers are at greater risk for a variety of pregnancy and birth complications:

Premature birth

Low birth weight

Down syndrome

Higher infant mortality rates


Other threats to prenatal development

Illness in a pregnant woman can have devastating consequences:

- Rubella (German measles) prior to the 11th week can cause blindness, deafness, heart defects, or brain damage.

- Chicken pox and mumps may cause birth defects and miscarriage, respectively.

- Syphilis and gonorrhea can be transmitted to the child.


Babies born with AIDS can have birth abnormalities including small, misshapen faces, protruding lips, and brain deterioration.

90 percent have neurological delays and deficits in motor coordination, speech, and facial expression.

They are susceptible to infection.

Survival past infancy is rare.

More threats to prenatal development

Mother's use of legal and illegal drugs pose serious risks to the unborn child:

- Aspirin can lead to bleeding.

-Thalidomide caused missing limbs.

-Marijuana restricts oxygen to the fetus.

-Cocaine restricts blood flow and oxygen, babies are born addicted and go through withdrawal; they are shorter and weigh less; they have serious respiratory problems and birth defects or seizures; it is often impossible to soothe them.

Still more threats to prenatal development

Both alcohol and cigarettes can disrupt the development of the fetus:

Just two drinks a day has been associated with lower intelligence.

FETAL ALCOHOL SYNDROME (FAS) is a disorder caused by the pregnant mother consuming substantial quantities of alcohol during pregnancy potentially resulting in mental retardation, delayed growth, and facial deformities.

FETAL ALCOHOL EFFECTS (FAE) - Some, not all, of FAS symptoms due to motherís alcohol consumption.

Threats to Prenatal Development

Smoking reduces the oxygen content and increase carbon monoxide; babies can miscarry or are born with abnormally low birth weight; babies born to smokers are shorter and may be intellectually delayed.



Fathers can affect the prenatal environment.

Fathers should avoid second hand smoke that may affect mother and childís health.

Fatherís alcohol and drug use may impair sperm and lead to chromosomal damage that may affect fetus.

Alcohol use by father may cause stress on mother.

Fatherís exposure to environmental toxins like mercury or lead may cause genetic damage to sperm and cause birth defects.

Physically and emotionally abusive fathers may cause damage to unborn children by raising maternal stress or causing actual physical damage to child.

Optimizing the Prenatal Environment

Limit x-rays

Avoid birth control pills for 3 months before trying to conceive

Get vaccinated against German measles

Eat well

Donít use alcohol or drugs

Monitor caffeine intake

Donít smoke

Exercise regularly