Week 2: Genetic and Infancy

DNA

The molecule containing chemical instructions for cells to manufacture proteins.

Chromosome

A structure made of DNA and protein carrying genetic information.

Typical human chromosome number

46 chromosomes arranged in 23 pairs: 44 autosomes and 2 sex chromosomes.

Gene

A segment of DNA containing instructions for a functional product; a basic unit of heredity.

Genome

The complete set of genetic information.

Allele

A version of a gene; an individual usually inherits one allele from each parent for an autosomal gene.

Genotype

A person's genetic makeup.

Phenotype

Observable characteristics resulting from genetic makeup and environmental influences.

Carrier of an autosomal recessive disorder

A person with one disease-associated allele who usually does not show the recessive disorder.

Dominant inheritance

One copy of a dominant allele can produce the associated trait.

Recessive inheritance

For a typical autosomal recessive disorder, two disease-associated alleles are needed to express the disorder.

Homozygous vs. heterozygous

Homozygous means two matching alleles; heterozygous means two different alleles.

Punnett square

A diagram showing possible allele combinations and probabilities for offspring.

Aa × Aa: genotype probabilities

25% AA, 50% Aa, and 25% aa for each pregnancy.

Two carriers of an autosomal recessive disorder: offspring probabilities

25% affected, 50% unaffected carriers, and 25% unaffected noncarriers for each pregnancy.

Aa × aa for a dominant disorder

If A causes the disorder, each pregnancy has a 50% chance of an affected child and 50% chance of an unaffected child.

Does one child's genotype change the next child's genetic probability?

No. Each pregnancy is a separate probability event.

Typical sex-chromosome patterns

XX for female and XY for male; an egg contributes X, while a sperm contributes X or Y.

X-linked recessive inheritance

A recessive allele on the X chromosome is usually expressed in an XY individual with one affected X.

Why are X-linked recessive traits more often expressed in males?

Males typically have one X chromosome, so there is no second X allele to mask the recessive allele.

Carrier mother and unaffected father: X-linked recessive sons

Each son has a 50% chance of being affected and a 50% chance of being unaffected.

Carrier mother and unaffected father: X-linked recessive daughters

Each daughter has a 50% chance of being a carrier and a 50% chance of being a noncarrier.

Can a father pass an X-linked allele directly to a son?

No. A father usually passes his Y chromosome to sons and his X chromosome to daughters.

Down syndrome

A chromosomal condition typically involving an extra chromosome 21, called trisomy 21.

Examples of autosomal recessive disorders in the lecture

Cystic fibrosis, thalassemia, and sickle-cell disease.

Genetic counseling

Helping families understand inheritance, testing, and the risk of inherited conditions.

Gene therapy

Introducing or modifying genetic material to address a missing or defective gene function.

Germinal period

The first 2 weeks after conception; rapid cell division and early differentiation occur.

Embryonic period

Weeks 3-8 after conception; basic body structures develop.

Fetal period

Week 9 after conception until birth; growth and functional maturation continue.

Zygote

The cell formed when sperm and egg unite.

Implantation

Attachment of the developing organism to the uterine lining.

Why is the embryonic period especially vulnerable to structural abnormalities?

Major organs and body structures are forming during this period.

Dizygotic twins

Fraternal twins from two eggs fertilized by two different sperm.

Monozygotic twins

Identical twins from one fertilized egg that divides into two developing organisms.

Examples of prenatal teratogens

Alcohol, drugs, radiation, lead, and infection such as toxoplasmosis.

Prenatal health-promotion priorities

Nutrition, appropriate activity, prenatal care, avoidance of teratogens, and support for adjustment to pregnancy.

Newborn age range for this exam

Birth-1 month.

Infant age range for this exam

1-12 months.

Apgar assessment: five categories

Appearance/color, pulse, grimace/reflex response, activity/muscle tone, and respiration.

When is the Apgar score usually assessed?

At 1 minute and 5 minutes after birth.

Apgar scoring

Each of five categories receives 0, 1, or 2 points; total possible score is 10.

Apgar result emphasized in the slides

A score of 7 or above is generally reassuring.

Rooting reflex

Touching the cheek or mouth area makes the newborn turn toward the stimulus to seek feeding.

Sucking reflex

The newborn sucks when the mouth is stimulated.

Palmar grasp reflex

The newborn closes the hand around an object placed in the palm.

Moro reflex

A startle response involving extension of the arms followed by drawing them inward.

Tonic neck reflex

Turning the head produces the "fencing" posture: extension on the face side and flexion on the opposite side.

Babinski reflex in an infant

Stroking the sole can cause the great toe to extend and the other toes to fan.

Stepping reflex

When supported upright with feet touching a surface, a newborn makes stepping movements.

Growth vs. development

Growth is increased physical size; development is increased function and mastery of skills.

Cephalocaudal development

Development proceeds from head toward feet.

Proximodistal development

Development proceeds from the body's center toward the extremities.

Infant weight milestones

Birth weight doubles by about 6 months and triples by about 1 year.

Infant length change in the first year

Length increases by approximately 50% from birth.

What do growth charts show?

Percentiles and growth trends for measurements such as weight, length, and head circumference.

A 6-month-old is in the 20th weight percentile. What does this mean?

The infant weighs more than about 20% and less than about 80% of the reference group; the percentile alone does not diagnose malnutrition.

Gross motor skills

Large-muscle movements such as sitting, standing, walking, and jumping.

Fine motor skills

Small-muscle movements, especially controlled hand and finger actions.

Gross motor table: sitting with head steady

About 3 months for 50% of infants and 4 months for 95%, according to the lecture table.

Gross motor table: sitting unsupported

About 6 months for 50% of infants and 7 months for 95%

Gross motor table: pulling to stand

About 9 months for 50% of infants and 10 months for 95%

Gross motor table: standing alone

About 12 months for 50% of infants and 14 months for 95%, according to the lecture table.

Gross motor table: walking well

About 13 months for 50% of infants and 15 months for 95%

Are milestone ages exact deadlines for every child?

No. They describe typical patterns and variation; interpret progress in context.

Neuron

A nerve cell that receives and transmits information.

Axon

The part of a neuron that transmits signals away from the cell body.

Dendrite

A branching part of a neuron that receives signals.

Synapse

The connection where one neuron communicates with another.

Neurotransmitter

A chemical messenger carrying information between nerve cells.

Synaptic pruning

Removal of less-used neural connections as the brain develops.

Head sparing

Relative protection of brain growth when malnutrition slows growth elsewhere in the body.

Why do infants need stimulation?

Varied sensations, play, and movement support developing brain connections.

Why can severe stress affect infant development?

Excessive stress-hormone exposure can interfere with developing brain function.

Most advanced newborn sense emphasized in the lecture

Hearing.

Least mature newborn sense emphasized in the lecture

Vision.

SUID

Sudden unexpected infant death: death before age 1 with no immediately obvious cause.

SIDS

Sudden infant death syndrome: an infant death that remains unexplained after a thorough investigation.

Purpose of immunization

To prepare the immune system to resist a particular disease and reduce disease spread.

Infant feeding sequence

Exclusive breastfeeding for the first 6 months, then introduction of complementary foods.

Stunting

Low height for age associated with chronic malnutrition.

Wasting

Low weight for height associated with malnutrition.

Marasmus

Severe malnutrition with marked weight loss, dehydration, and wasting, often before age 1.

Kwashiorkor

Malnutrition involving edema, poor growth, and hair changes, often after age 1.

Primary teeth

The 20 deciduous or baby teeth.

When does teething begin in the slides?

Around 5-7 months.

Nursing caries

Tooth decay associated with prolonged exposure to milk or juice, including bottles at bedtime.

Object permanence

Understanding that an object continues to exist even when it cannot be seen.

When does object permanence begin in the lecture?

Around 7 months.

A baby searches for a toy hidden under a cloth. What concept?

Object permanence.

Piaget's sensorimotor stage

Birth-2 years; thinking and learning through senses and movement.

Sensorimotor stage 1

Birth-1 month: reflexes.

Sensorimotor stage 2

1-4 months: first adaptations or habits; primary circular reactions.

Sensorimotor stage 3

4-8 months: repeating interesting effects on the environment; secondary circular reactions.

Sensorimotor stage 4

8-12 months: intentional coordination of actions and means-to-an-end behavior.

Sensorimotor stage 5

12-18 months: active experimentation; tertiary circular reactions.

Sensorimotor stage 6

18-24 months: mental combinations and early internal representation.

Primary circular reaction

Repeating an action centered on the infant's own body.

Secondary circular reaction

Repeating an action because of an interesting effect on an object or the environment.

Tertiary circular reaction

Varying actions to explore new results.