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2: Heredity, Prenatal Development, and Birth

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    Learning Objectives: Heredity
    • Define genes
    • Distinguish between mitosis and meiosis, genotype and phenotype, homozygous and heterozygous, and dominant and recessive
    • Describe some genetic disorders, due to a gene defect, and chromosomal disorders
    • Define polygenic and incomplete dominance
    • Describe the function of genetic counseling and why individuals may seek genetic counseling
    • Define behavioral genetics, describe genotype-environment correlations and genotype-environmental interactions, and define epigenetics

    In this chapter, we will begin by examining some of the ways in which heredity helps to shape the way we are. We will look at what happens genetically during conception, and describe some known genetic and chromosomal disorders. Next we will consider what happens during prenatal development, including the impact of teratogens. We will also discuss the impact that both the mother and father have on the developing fetus. Next we will present the birth process and some of the complications that can occur during delivery. Before going into these topics, however, it is important to understand how genes and chromosomes affect development.

    • 2.1: Heredity
      As your recall from chapter one, nature refers to the contribution of genetics to one’s development. The basic building block of the nature perspective is the gene. Genes are recipes for making proteins, while proteins influence the structure and functions of cells. Genes are located on the chromosomes and there are an estimated 20,500 genes for humans, according to the Human Genome Project.
    • 2.2: Genotypes and Phenotypes
      The word genotype refers to the sum total of all the genes a person inherits. The word phenotype refers to the features that are actually expressed. Because genes are inherited in pairs on the chromosomes, we may receive either the same version of a gene from our mother and father, that is, be homozygous for that characteristic the gene influences. If we receive a different version of the gene from each parent, that is referred to as heterozygous.
    • 2.3: Genetic Disorders
      Most of the known genetic disorders are dominant gene-linked; however, the vast majority of dominant gene linked disorders are not serious or debilitating. For example, Huntington's Disease is a dominant gene linked disorder that affects the nervous system and is fatal, but does not appear until midlife. Recessive gene disorders, such as cystic fibrosis and sickle-cell anemia, are less common but may actually claim more lives.
    • 2.4: Chromosomal Abnormalities
      A chromosomal abnormality occurs when a child inherits too many or two few chromosomes. The most common cause of chromosomal abnormalities is the age of the mother. As the mother ages, the ovum is more likely to suffer abnormalities due to longer term exposure to environmental factors. Consequently, some gametes do not divide evenly when they are forming. Therefore, some cells have more than 46 chromosomes.
    • 2.5: Behavioral Genetics
      Behavioral Genetics is the scientific study of the interplay between the genetic and environmental contributions to behavior. Often referred to as the nature/nurture debate, Gottlieb (1998, 2000, 2002) suggests an analytic framework for this debate that recognizes the interplay between the environment, behavior, and genetic expression. This bidirectional interplay suggests that the environment can affect the expression of genes just as genetic predispositions can impact a person’s potentials.
    • 2.6: Prenatal Development
      Now we turn our attention to prenatal development which is divided into three periods: The germinal period, the embryonic period, and the fetal period. The following is an overview of some of the changes that take place during each period.
    • 2.7: Teratogens
      The developing child is most at risk for some of the most severe problems during the first three months of development. Unfortunately, this is a time at which many mothers are unaware that they are pregnant. Today, we know many of the factors that can jeopardize the health of the developing child. The study of factors that contribute to birth defects is called teratology. Teratogens are environmental factors that can contribute to birth defects.
    • 2.8: Maternal Factors
      Most women over 35 who become pregnant are in good health and have healthy pregnancies. However, according to the March of Dimes (2016d), women over age 35 are more likely to have an increased risk of: Fertility problems High blood pressure Diabetes Miscarriages Placenta Previa Cesarean section Premature birth Stillbirth A baby with a genetic disorder or other birth defects.
    • 2.9: 2.9 Prenatal Assessment
      A number of assessments are suggested to women as part of their routine prenatal care to find conditions that may increase the risk of complications for the mother and fetus (Eisenberg, Murkoff, & Hathaway, 1996). These can include blood and urine analyses and screening and diagnostic tests for birth defects.
    • 2.10: Complications of Pregnancy
    • 2.11: Birth
      Prepared childbirth refers to being not only in good physical condition to help provide a healthy environment for the baby to develop, but also helping individuals to prepare to accept their new roles as parents. Additionally, parents can receive information and training that will assist them for delivery and life with the baby. The more future parents can learn about childbirth and the newborn, the better prepared they will be for the adjustment they must make to a new life.
    • 2.12: Assessing the Neonate
      The Apgar assessment is conducted one minute and five minutes after birth. This is a very quick way to assess the newborn's overall condition. Five measures are assessed: Heart rate, respiration, muscle tone (assessed by touching the baby's palm), reflex response (the Babinski reflex is tested), and color. Another way to assess the condition of the newborn is the Neonatal Behavioral Assessment Scale (NBAS). The baby's motor development, muscle tone, and stress response are assessed.
    • 2.R: Heredity, Prenatal Development, and Birth (References)

    This page titled 2: Heredity, Prenatal Development, and Birth is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Martha Lally and Suzanne Valentine-French via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.