28 Chapter 28 Development and Inheritance
By Aylin Marz
Motivation.
Infant mortality is the death of an infant before his or her first birthday. The infant mortality rate is the number of infant deaths for every 1,000 live births. In addition to giving us key information about maternal and infant health, the infant mortality rate is an important marker of the overall health of a society. In 2020, the infant mortality rate in the United States was 5.4 deaths per 1,000 live births.
Almost 20,000 infants died in the United States in 2020. The five leading causes of infant death in 2020 were:
- Birth defects.
- Preterm birth and low birth weight.
- Sudden infant death syndrome.
- Injuries (e.g., suffocation).
- Maternal pregnancy complications.
Racial and ethnic disparities are abundant and show that African American mothers lose their infants at an alarmingly higher rate than majority/white mothers (Figure 28.1). This is disturbing and we need to better understand how to improve maternal and infant health to fix this problem.
Learning Objectives
Upon completion of the work in this chapter students should be able to:
- Apply knowledge of fertilization and reproductive anatomy to a scenario on IVF success
- Describe the features of embryonic and fetal development using models
- Create models of Punnett squares to determine the outcome of crosses for different types of hereditary diseases
Background.
Fertilization
Hundreds of millions of sperm deposited in the vagina travel toward the oocyte, but only a few hundred actually reach it. The number of sperm that reach the oocyte is greatly reduced because of conditions within the female reproductive tract. Many sperm are overcome by the acidity of the vagina, others are blocked by mucus in the cervix, whereas others are attacked by phagocytic leukocytes in the uterus. Those sperm that do survive undergo a change in response to those conditions. They go through the process of capacitation, which improves their motility and alters the membrane surrounding the acrosome, the cap-like structure in the head of a sperm that contains the digestive enzymes needed for it to attach to and penetrate the oocyte.
The oocyte that is released by ovulation is protected by a thick outer layer of granulosa cells known as the corona radiata and by the zona pellucida, a thick glycoprotein membrane that lies just outside the oocyte’s plasma membrane. When capacitated sperm make contact with the oocyte, they release the digestive enzymes in the acrosome (the acrosomal reaction) and are thus able to attach to the oocyte and burrow through to the oocyte’s zona pellucida. One of the sperm will then break through to the oocyte’s plasma membrane and release its haploid nucleus into the oocyte. The oocyte’s membrane structure changes in response (cortical reaction), preventing any further penetration by another sperm and forming a fertilization membrane. Fertilization is complete upon unification of the haploid nuclei of the two gamet