Prenatal Development

Monozygotic (identical) twins

Genetically identical twins formed when a cluster of cells splits apart within the first two weeks of development. This means one zygote splits into two embryos.

Dizygotic (fraternal) twins

Twins who are no more genetically similar than any two siblings; they occur when two ova are fertilized by two separate sperm, meaning two zygotes form separately.

3+ births

Multiple births (e.g., triplets, quadruplets) that can be produced either monozygotically, dizygotically, or both (a combination of a splitting zygote and separately fertilized ova).

Twin studies

Research that compares the average similarity of monozygotic twins on a given outcome to that of dizygotic twins on a different outcome to estimate genetic influence.

Adoption studies

Research that compares an individual to their twin who has a different developmental environment to distinguish between genetic and environmental effects.

Genotype

The specific combination of genetic material present in an organism.

Phenotype

The observable traits or characteristics of an organism, which are a result of the genotype and environmental interactions.

Ultrasound sonography

A prenatal testing method that uses high-frequency sound waves to scan the mother’s womb and produce an image of the fetus.

Genetic Counseling

A service that tests for inherited disorders by assembling a karyotype, which is a chart with photos of an individual's chromosomes.

Chorionic Villus Sampling (CVS)

A prenatal test performed at 8-10 weeks of pregnancy where a needle is inserted into the placenta to collect fetal cells for genetic testing.

Amniocentesis

A prenatal procedure performed between 15-20 weeks of pregnancy that examines fetal cells found in the amniotic fluid for genetic abnormalities.

Nature vs Nurture debate

An ongoing discussion that explores how genes (nature) and environmental factors (nurture) interact and influence development.

Epigenetics

Changes in gene expression that do not involve alterations to the underlying DNA sequence itself. These changes help explain how environment can influence gene expression and phenotype.

Histone modification

A type of epigenetic change involving chemical alterations to histones, which are the proteins around which DNA is wrapped.

DNA methylation

An epigenetic mechanism involving the addition of a methyl group to cytosine bases in DNA, which can lead to the suppression of gene expression.

Multifactorial Transmission

The concept that a given genotype can express a range of phenotypes depending on an infinite combination of environmental factors.

Gene-Environment Interaction (Scarr’s Theory)

Sandra Scarr's theory explaining how genes influence environment and vice versa, through mechanisms like children gravitating towards environments aligning with their genetic abilities (gene–environment correlation) and temperament evoking specific environmental responses (evocative gene–environment correlation).

Preconception Epigenetics and Health

The impact of parental health (both maternal and paternal) before conception on offspring outcomes, particularly through epigenetic changes like DNA methylation and non-coding RNA in sperm, influencing a child's health risks for conditions such as metabolic diseases.

Gametes

Reproductive cells (sperm and ovum) that contain genetic information.

Zygote

A single cell formed when a sperm fuses with an ovum during fertilization.

Embryo

The rapidly developing group of cells from the end of the second week through the eighth week of development.

Fetus

The developmental stage from the ninth week onward, characterized by rapid body growth and maturation of organs.

Fertilization

The process of a sperm and ovum joining to create a zygote, marking the beginning of the germinal stage.

Germinal Stage

The first stage of prenatal development, lasting from fertilization to 2 weeks, during which the zygote implants into the uterine wall and the placenta forms.

Embryonic Stage

The second stage of prenatal development, from 2 weeks to 8 weeks, where the zygote becomes an embryo and differentiates into three germ layers: ectoderm, endoderm, and mesoderm.

Ectoderm

One of the three germ layers of the embryo, which forms skin, hair, teeth, sense organs, brain, and spinal cord.

Endoderm

One of the three germ layers of the embryo, which forms the digestive system, liver, pancreas, and respiratory system.

Mesoderm

One of the three germ layers of the embryo, located between the ectoderm and endoderm, which forms muscles, bones, and blood.

Fetal Stage

The final stage of prenatal development, from 8 weeks to birth, characterized by dramatic increases in size and weight, and the operationalization of organs.

Teratogens

Environmental factors that can cause developmental abnormalities in a fetus, posing ethical challenges for research due to sensitivity and variability of exposure.

Fetal Alcohol Spectrum Disorder (FASD)

A range of conditions caused by alcohol use during pregnancy, associated with delayed growth, intellectual disability, and deformities.

Cannabis (Weed) During Pregnancy

While evidence is more limited than for alcohol, THC exposure during pregnancy may be linked to low birth weight and neurological issues; avoiding cannabis during breastfeeding is also recommended.

Cocaine

A substance with risks during pregnancy including premature birth, placental abruption, neurological issues, and seizures, which can also be transmitted through breast milk.

Opiates

Substances whose use during pregnancy carries risks such as placental abruption, premature birth, preeclampsia, and neonatal opiate withdrawal syndrome.

Neonatal Withdrawal Syndrome (NAS)

A cluster of symptoms (e.g., seizures, poor feeding, sleep disruption, dehydration, hyperactive reflexes) that can occur in newborns as they withdraw from substances (like opioids) to which they were exposed before birth.

Bisphenol A (BPA)

A known endocrine disruptor used in plastics since the 1950s, linked to adverse health effects such as breast and prostate cancer, obesity, neurobehavioral problems, and reproductive abnormalities, even at very low doses.

Mercury and Fish Consumption

Excessive mercury levels from fish consumption during pregnancy can risk fetal brain development; health guidance recommends choosing low-mercury fish and limiting high-mercury options.

Stress and the HPA Axis

Stress during pregnancy, especially chronic stress or extreme events, can negatively affect fetal development through elevated cortisol levels, which can disrupt the HPA axis.

The Mozart Effect

The widely publicized but largely unsupported idea that listening to Mozart prenatally can increase intelligence. While fetuses perceive rhythm and sound, there's no unique IQ benefit from Mozart.

Fetal Perception and Preferences

The ability of fetuses to perceive stimuli and potentially develop preferences, such as food preferences, before birth.