Population Genetics

The prenatal period begins with the formation of the embryo and continues through the development of the fetus, terminating with birth. Neonatal physiology during prenatal life differs significantly from that during postnatal life. Before birth, nutrient, gas exchange, and elimination of waste products occur via the placenta. The fetus receives oxygenated blood via the umbilical vein, and deoxygenated blood is removed via the umbilical arteries. The 3 shunts that help redirect the fetal circulation are the ductus venosus, foramen ovale, and ductus arteriosus. These shunts close after birth, leaving behind vestigial remnants. Postnatally, the fetal circulatory system and organ systems adapt to the extrauterine environment. Placental blood supply is cut off, causing the neonate to make adaptive changes.

Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Chromosomal mutations occur when an abnormal number of chromosomes is inherited. Point mutations occur when a nucleotide is swapped for another nucleotide and can be missense, nonsense, or silent mutations. Frameshift mutations occur when a nucleotide is added or deleted, and expansion mutations occur when a given trinucleotide sequence is repeated along the chromosome. Genetic mutations are the basis for most inherited diseases. Common disorders caused by DNA mutations include sickle cell disease, Huntington disease, and Tay-Sachs disease.

Prenatal care is a systematic and periodic assessment of pregnant women during gestation to assure the best health outcome for the mother and her fetus. Prenatal care prevents and identifies maternal and fetal problems that adversely affect the pregnancy outcome. Prenatal visits involve scheduled screening tests such as prenatal ultrasounds or blood glucose tests and measurements of fetal/maternal health metrics. These visits are also opportunities to educate pregnant women about pregnancy, labor, delivery, and parenting while providing psychological support to patients and their families.

Population genetics is a field in genetics that is concerned with the differences in the gene pool between different populations and how this underlies phenotypic differences between populations. The Hardy-Weinberg equilibrium serves as a basis for studying genetic variation within a population and allows for the calculation of allelic frequency. The process of natural selection is what determines the allelic frequencies in the population and the variability in the genotype-phenotype relationships between species.

Amino acids are the building blocks of proteins, whose production is a tightly regulated enzymatic cascade. Disorders of the enzymes involved in amino acid metabolism are often serious and present early in life. Congenital errors in amino acid metabolism are due to either impaired synthesis or degradation. In the United States, neonates are routinely screened at birth for common disorders of amino acid metabolism, which include phenylketonuria (PKU), maple syrup urine disease (MSUD), homocystinuria, tyrosinemia, and alkaptonuria. Symptoms of these conditions often present early in life. Although treatment varies, most of these conditions require dietary changes, and some require protein supplementation or other medication regimens.