Lifespan Development. Tara L. Kuther

the mother. The Y chromosome was inherited from the father. Each daughter has two X chromosomes. One X chromosome was inherited from the mother. The other was inherited from the father.

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      A father and mother, both with brown hair, have four children. Three have brown hair and one has red hair.

      Parent genotype: capital N, lowercase r for both parents.

      Child genotype:

      1. Son with brown hair: capital N, capital N. He received the dominant gene from both his father and mother.

      2. Daughter with brown hair: capital N, lowercase r. She received the dominant gene from her mother and the recessive gene from her father.

      3. Second daughter with brown hair: capital N, lowercase r. She received the dominant gene from her father and the recessive gene from her mother.

      4. Daughter with red hair: lowercase r, lowercase r. She received the recessive gene from both her father and mother.

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      For both examples, the mother, father, and offspring are represented as either black or white silhouettes.

      Example 1: Abnormal chromosome arises from the father. The father, shaded black, and the mother, shaded white, have two children: one boy, shaded black, and one girl, shaded black.

      Example 2: Abnormal chromosome arises from the mother. The father, shaded black, and the mother, shaded white, have two children: one boy, shaded white, and one girl, shaded white.

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      The following attributes are shown or described on the illustration of the child:

      Slower growth

      Intellectual disability

      Flat back of head

      Small ears

      Short nose

      A single line across the palm of the head (palmar crease)

      Intestinal blockage

      Poor muscle tone or loose joints

      Shorter in height as children and adults

      Broad, flat face

      Almond-shaped eyes that slant up

      Small and arched palate

      Big, wrinkled tongue

      Dental anomalies

      Short and broad hands

      Congenital heart disease

      Enlarged colon

      Big toes widely spaced

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      Three genotypes are shown, labeled A, B, and C. For each genotype, there is a different range of reaction possible. In this example, the range relates to intelligence performance (IQ). If the person’s environment is deprived, the genotype achieves only the lowest range of reaction. If the person’s environment is average, the genotype achieves only the middle range of reaction. If the person’s environment is enriched, the genotype achieves the highest range of reaction.

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      Active gene–environment: Low degree of influence in infancy. Sharp increase to medium to high level in childhood, followed by slower increase throughout adolescence and adulthood, ending with a high level in adulthood.

      Evocative gene–environment: Medium degree of influence across all stages.

      Passive gene–environment: High degree of influence in infancy, with a sharp decline throughout adolescence, reaching a level of medium to low. The degree of influence continues to decrease throughout adolescence and adulthood, ending with a low level in adulthood.

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      A line is shown to the side of each bidirectional influence listed. On each line there are a series of arrows. The arrows are shown in a repeating pattern of one arrow pointing diagonally up to the next line and the next pointing diagonally back down.

      Below the graphic is a right-pointing arrow that extends the width of the lines above. The label reads Individual Development.

      3 The Prenatal Period, Birth, and the Newborn

      Tara L. Kuther

      John Cancalosi / Alamy Stock Photo

      Looking down at his newborn daughter’s face, Remmy said admiringly, “Carla looks just like you.” His wife, Darla, replied, “That’s what my mother said.” “I’m in awe,” said Remmy. “Less than a year ago we decided to start a family and now, seemingly overnight, here she is. It’s magical—over a few short months, this little person popped into existence from pixie dust!” Darla laughed and protested, “My baby girl was never pixie dust!”

      Remmy’s silly observation describes the dramatic process of prenatal development. Over 9 months, a single cell transforms and grows into a neonate, a newborn. Every infant is born with a unique set of characteristics that reflect the genetic makeup of both parents. In this chapter, we discuss the process of how prenatal development unfolds, how a baby is born, and what the newborn baby is like.

      Learning Objectives

       3.1 Describe the three periods of prenatal development that begin with conception.

       3.2 Identify how exposure to teratogens can influence the prenatal environment.

       3.3 Explain the process of childbirth.

       3.4 Discuss the neonate’s physical capacities, including development in low-birthweight infants.

      Prenatal Development

      Remarkably, a human infant progresses from fertilization to birth in just 266 days, or 38 weeks. Conception, the union of ovum and sperm, marks the beginning of prenatal development, the transformative process in which the fertilized ovum, known as a zygote, progresses through several periods of development, finally emerging from the womb as a neonate. Prenatal development takes place over several stages representing shifts in the developmental processes.

      Conception

      A woman can conceive only during a short window of time each month. About every 28 days, an ovum bursts from one of the ovaries into the long, thin fallopian tube that leads to the uterus; this event is known as ovulation (see Figure 3.1). The ovum is the largest cell in the human body, yet it is only 1/175th of an inch in diameter (about the size of the period at the end of this sentence). Over several days, the ovum travels down the fallopian tube while the corpus luteum, the spot on the ovary from which the ovum was released, secretes hormones that cause the lining of the uterus to thicken in preparation for the fertilized ovum (Sadler, 2015). If fertilization does not occur, the lining of the uterus is shed through menstruation about 2 weeks after ovulation.

      The tiny sperm is fertilizing the much larger ovum.

      F. Leroy / Science Source

      Conception, of course, also involves the male. Each day, a man’s testes produce millions of sperm, which are composed of a pointed head packed with 23 chromosomes’ worth of genetic material and a long tail. During ejaculation, about 360 million, and as many as 500 million, sperm are released, bathed in a protective fluid called