Chapter 2 Beginning

Embryonic Period

(3rd through 8th week): basic forms of all body structures develop

Fetal period

(9th week until birth): fetus grows in size and matures in functioning.

Implantation

(about 10 days after conception) Developing organism burrows into the placenta that lines the uterus.

Germinal period

(first two weeks after conception): rapid cell division and beginning of cell differentiation

Triplet variations

Variations occur because DNA code contains about 3 billion pairs of chemicals organized into triplets. Copy number variations include small variations, mutations, or repetitions in base pairs not always found in other versions of the same gene.

Worldwide low weight births

When all nations are included, 47 report LBW at 6 per 100 or lower, which suggests that many nations (including the United States and United Kingdom) could improve national health, since both are affected by the same causes.

X-linked

a gene carried on the X chromosome. If a male inherits an X-linked recessive trait from his mother, he expresses that trait because the Y from his father has no counteracting gene. Females are more likely to be carriers of X-linked traits but are less likely to express them.

All living things are

composed of cells that promote growth and sustain life according to instructions in their molecules of DNA.

Uncertain Sex

every now and then, a baby is born with "ambiguous genitals" meaning that the child's sex is not abundantly clear. When this happens, a quick analysis of the chromosomes is needed to make sure there are exactly 46 and to see whether the 23rd pair is XY or XX.

Multifactorial

influenced by many factors

Fetal brain

signals the release of hormones to trigger the female's uterine muscles.

Zygote begins duplication and division

within hours of conception

Humans usually possess _____ chromosomes

46 (44 autosomes and 2 sex chromosomes)

First Stages of the Germinal Period

:The original zygote as it divides into (a) two cells, (b) four cells, and (c) eight cells. Occasionally at this early stage, the cells separate completely, forming the beginning of monozygotic twins, quadruplets, or octuplets.

Apgar scale

A quick assessment of a newborn's body functioning. The baby's heart rate, respiratory effort, muscle tone, color and reflexes are given a score of 0,1, or 2 twice at one minute and five minutes after birth - and each time the total of all five scores is compared with the ideal score of 10 (which is rarely attained).

Chromosomal anomalies

About once in every 200 births, an infant is born with 45, 47, or even 48 or 49 chromosomes which produces syndrome. Most common condition is Down syndrome (trisomy-21). About 1 in every 500 infants is born with only one sex chromosome (no Y) or with three or more. Odd number of chromosomes correlated with advanced age in parents. Everyone is a carrier of genes or alleles that could produce serious diseases or handicaps in the next generation. It is likely that "common complex disorders arise from an accumulation of genetic defeats of genetic defects in many genes."

Additive genes

Add something to some aspect of the phenotype. Add up to make the phenotype.

Age of viability

Age at which a preterm newborn may survive outside the mother's uterus if medical care is available. About 22 weeks after conception Brain is able to regulate basic body functions Chances of survival increase with each day after the 22 week mark 25 weeks post-conception is viable, although very small. At full term (38 weeks) weight gain would mean that the limbs are folded close to the body, and the uterus is almost completely full.

Behavioral teratogens

Agents and conditions that can harm the prenatal brain, impairing the future child's intellectual and emotional functioning.

Genotype

An organism's genetic inheritance, or genetic potential. Unique for each organism.

reflex

An unlearned, involuntary action or movement in response to a stimulus, a reflex occurs without conscious thought.

Teratogens

Any agent or condition, including viruses and drugs, resulting in birth defects or complications. Not all teratogens can be avoided. Structural abnormalities are obvious at birth.

Labor begins

Average duration for firstborn babies: 12 hours Quicker labor for later-born babies

Embryonic Period (3rd through 8th week)

Begins when the primitive streak appears down the middle of the cell mass Primitive streak becomes the neural tube and later forms the brain and spine of the CNA. Head takes shape. Eyes, ears, nose, and mouth form. Heart begins to pulsate. Extremities develop and webbed fingers and toes separate.

Preterm

Birth that occurs at 35 or fewer weeks after conception. Usually associated with low birthweight.

Small for gestational age

Birthweight is significantly lower than expected, given the time since conception. Suggests impairment throughout prenatal development and serious problems.

Fetal Period (from 9th week until birth)

Developing human organism from the start of the 9th week after conception until birth. Heartbeat detectable via stethoscope. Cortex is not fully mature at birth (e.g. prefrontal lobes). Genitals form and sex hormones cause differences in fetal brain organization. At 3 months, the fetus weighs about 3 ounces. Experiences the period of the greatest brain growth during the 4th, 5th, and 6th months.

Regulator genes

Direct the interactions of other genes, controlling their genetic expression, duplication, and transcription. Are responsible for difference between species.

Dominant- Recessive Heredity

Dominant gene is far more influential than the recessive gene (non-additive). Dominant gene can completely control the phenotype with no noticeable effect of recessive gene. Effect of recessive genes can sometimes be noticed.

Alcohol

Embryos exposed to mother's heavy drinking can develop fetal alcohol syndrome (FAS).

High risk infants and children

Every developmental accomplishment is late. Cry more, pay attention less, disobey more, and experience language and developmental outcome delays.

Human Genome Project

Found "only" about 20,000-23,000 genes in humans. Exact number is unknown. (23rd pair XX or XY)

Making predictions and reducing risks

General maternal health is protective Scrutinize more closely herbal medicine or over-the-counter rugs. Learn about effects of psychoactive drugs and alcohol. Use Internet-based health information cautiously.

Infant mortality

Has decreased due to better medical care. Childbirth has become safer for mothers safer for mothers. Excessive medical care also has disadvantages.

Middle childhood, formerly SGA children

Have more neurological problems, smaller brain volume.

Father's role

Helping mother stay healthy Helping mother manage stress (affects fetus) Most fathers are helpful to their pregnant wives Paternal experiences of pregnancy and birth are called couvade- expected in some cultures, a normal variation in many, and considered pathological in others.

Traditional and Modern Birthing Practices

Home births, hospital births, Doula

Genome

Involves the full set of genes that are instructions to make an individual member of a certain species.

Low birthweight (LBW)

Less than 2,500 grams (5 1/2 pounds) at birth

Overall

Many genes are identical for every human being. Some genes vary slightly in their codes from one person to another.

Postpartum depression

Many women experience significant physical problems after birth Psychological symptoms range from "baby blues" to postpartum psychosis. May involve struggles with adequate baby care Varied causes. Sadness and inadequacy felt by 8-15% of new mothers in the days and weeks after giving birth Paternal involvement can have beneficial effect Causes for postpartum depression vary

Recessive disorders

Millions of different types, lethal conditions are rare.

DNA

Molecule that contains the chemical instructions for cells to manufacture various proteins. Promotes growth and sustains life.

Chromosomes

Molecules of DNA. Consists of 46 chromosomes arranged in 23 pairs.

Cystic fibrosis

More common among people with northern European ancestors. Carriers may have been protected against cholera.

Sickle-cell trait

Offers some protection against malaria. African carriers are more likely than non-carriers to survive.

Development of the placenta

Organ that surrounds the developing embryo and is attached to the wall of the uterus Sustains life via the umbilical chord (nourishes organism and carries waste products away).

Monozygotic (identical) twins

Originate from one zygote that splits apart very early in development. Incomplete split results in conjoined twins. Same genotype but slight variations in phenotype are possible due to environmental influences.

Carrier

Person whose genotype includes a gene that is not expressed in the phenotype. Unexpressed gene occurs in half of the carrier's gametes and is passed on to half of the carrier's offspring. Offspring can be carrier or express the gene in the phenotype (unexpressed gene is inherited by both parents).

Genetic Counseling

Professionals who provide genetic counseling help prospective parents understand their genetic risk so that they can make informed decisions, not impulsive, irrational ones.

Gametes

Reproductive cells (sperm and ova). Each gamete consists of 23 chromosomes.

Dizygotic (fraternal) twins

Result from fertilization of two separate ova by two separate sperm. Dizygotic twins have half their genes in common and occur twice as often as monozygotic twins. Incidence is genetic and varies by ethnicity and age.

United States low weight births

Steady increase in LBW over the past 25 years. 8% of newborns are seriously underweight ranking worse than most developed nations. More susceptible to teratogens, higher birth risks.

Genetic vulnerability

Some zygotes carry genes that make them vulnerable. Male fetuses are more vulnerable to teratogens than female ones. Neural-tube defects are more common in certain ethnic groups (e.g., Irish, English, and Egyptian). A particular example of differential sensitivity. Genetic protections or hazards are suspected for many birth defects.

Cesarean section

Surgical birth fetus can be removed quickly Usually safe for mother and baby, saving lives when the fetal head is too large for the pelvis. Lower rates in poorer countries (emergencies) Higher rates in richer countries (planned for the convenience of mother and/or obstetrician) 1/3 of births in the United States

Immigrant paradox

Surprising discovery that, although low SES correlates with poor health, this is not true for hispanics in the United States. Ex: when compared with the U.S. average LBW rate, Hispanic newborns are less often of low birthweight.

Phenotype

The observable characteristics of an organism, including appearance, personality, intelligence, and all other traits.

Gene disorders

The phenotype is only affected when the inherited gene is dominant or when both parents carry the recessive gene. Most dominant disorders begin in adulthood (fatal dominant childhood conditions cannot be passes on). Recessive disorders are most common. Ex: Huntington's disease, Cystic fibrosis, Thalassemia, Sickle-cel disease, Fragile X

Zygote

Two gametes combine and produce a new individual with 23 chromosomes from each parent.

Extremely low birthweight (ELBW)

Under 1,000 grams (2 pounds, 3 ounces) at birth

Very low birthweight (VLBW)

Under 1,500 grams (3 pounds, 5 ounces) at birth

Allele

Variation of gene or any of the possible forms in which a gene for a particular trait can occur. Effects of variations vary greatly from causing life-threatening conditions to having no detectable effect at all.

Doula

Woman who helps with labor, delivery, breast-feeding, and newborn care May be related to lower rate of cesarean sections

Polygenic

affected by many genes

Genetic diversity

distinguishes each person. Allows the human species to adapt to pressures of the environment.

Three periods of prenatal development

germinal, embryonic, fetal

The genes of chromosomes:

in the nucleus of each cell instruct the cell to manufacture the proteins needed to sustain life and development. The code for a protein is the particular combination of four bases, T-A-G-C.

Almost every trait is

polygenic and multifactorial

Brazelton Neonatal Behavioral Assessment Scale

records 46 behaviors, including 20 reflexes.