2.1 Genetics and Environment

Humans have forty-six paired chromosomes after receiving twenty-three, half of each pair, from each biological parent.
Genes are portions of the DNA sequence containing instructions for the body to make proteins that regulate development.
Genotype is the unique combination of individual genes, and phenotype is the way these genes express themselves physically and behaviorally.
Recessive genes exert their influence only in the absence of a dominant gene.
Different types of genetic inheritance (recessive/dominant, incomplete dominance, codominance) determine the way the inherited genes are expressed.
Most traits are influenced by numerous genes, and some genes influence multiple traits as well.
Sometimes errors occur during cell division that can cause inherited genetic disorders, such as sickle cell anemia or Down syndrome.
Genes and environments mutually influence gene expression, and phenotype is observed through epigenetic effects and gene-environment interactions.

2.2 Reproductive Systems and Conception

The components of the female reproductive system include the vagina, uterus, and fallopian tubes. The vagina is where sperm enter the female reproductive system, traveling through the uterus and up the fallopian tubes to an ovum or egg, which one sperm may fertilize in the process of conception.
The vas deferens, male urethra, and testicles are important parts of the male reproductive system. Sperm are created and stored within the testes, and if ejaculation occurs, sperm travel through the vas deferens to the urethra where they are ejected.
Individuals can become parents via sexual contact (intercourse), assisted reproductive technology (ART) methods such as IUI or IVF, via a surrogate who carries and births the child for the parent(s), or through adoption.
Social factors such as low income and lack of access to resources can pose obstacles that increase the chance of unintended pregnancies or prevent individuals from receiving treatment for infertility.

Prenatal development occurs in the germinal, embryonic, and fetal periods.
During the germinal period, conception occurs, and the fertilized egg passes through the fallopian tubes to the uterus where it implants into the uterine wall.
During the embryonic period, the implanted embryo divides into two parts. One becomes the infant, and the other develops into support structures. Organogenesis, or the creation of the body’s organs, also occurs during the embryonic period.
In the fetal period, the fetus grows, and the organs become refined.
The age of viability is the age at which a fetus born prematurely may have a chance of survival outside the womb.
Complications in prenatal development can be due to teratogen exposure or congenital disorders. These can cause spontaneous abortions.
A variety of prenatal tests may be recommended to monitor the health and development of the fetus. Several lifestyle factors and access to medical care can increase the likelihood of a healthy pregnancy.

Most U.S. births occur in hospitals, but those with low-risk pregnancies can also give birth in a birthing center or at home, often with the help of a midwife or other medical professional.
Options to ease the discomfort associated with childbirth include epidural injections and other medications, as well as natural childbirth methods. Other alternatives are water birth, acupuncture, and massage.
Once born, infants are given tests, including the Apgar test and the NBAS, to assess how well they are doing.
Infants born prematurely or with low birth weight often require extra medical attention and may be slower to attain developmental milestones.
Ways to prevent early birth and low birth weight include getting regular prenatal check-ups and care; making healthy choices regarding food, sleep, and exercise; avoiding excessive stress; and not smoking, drinking, or taking potentially harmful medications.

Navigating the first few weeks of parenthood can be difficult but rewarding. As the baby grows, so do parents.
Attachment is a two-way interaction between a child and a caregiver based on consistency of care.
Bonding with a newborn is a process and takes time, as does learning how to be a parent.
Postpartum depression and other struggles can occur in both mothers and fathers. Treatments are available.