Chapter 3

• Genetics in prenatal development

  The study of heredity and how it affects development before birth
• Evolutionary/Sociobiological


  • Fertilization is the process by which sperm and ovum combine to create a zygote, which then divides and develops into a baby
• Mechanisms of Heredity


  The science of genetics that studies the inborn factors inherited from biological parents that affect development
• Genetic Code


  DNA is the double-helix structure that contains the genetic information in the form of genes, which are functional units of heredity
• Meiosis


  Sex cells undergo division to produce cells with 23 chromosomes, which then fuse at conception to form a zygote with 46 chromosomes
• Mitosis


  Non-sex cells divide in half over and over again, replicating the DNA so each new cell has the same DNA structure
• Sex determination


  Males have an X and a Y chromosome, females have two X chromosomes. The combination determines the sex of the baby
• Alleles


  Two or more alternative forms of a gene that occupy the same position on paired chromosomes and affect the same trait
• Homozygous


  Possessing two identical alleles for a trait
• Heterozygous


  Possessing differing alleles for a trait
• Dominant inheritance


  Pattern where the dominant allele is expressed when a child receives different alleles
• Recessive inheritance


  Pattern where a child receives identical recessive alleles, resulting in expression of a non-dominant trait
• Polygenic inheritance


  Multiple genes at different sites affect a complex trait
• Mutations


  Permanent alterations in genes or chromosomes that may produce harmful characteristics
• Genotype


  Genetic makeup of a person, containing both expressed and unexpressed characteristics
• Phenotype


  Observable characteristics of a person
• Multifactorial transmission


  Combination of genetic and environmental factors to produce certain complex traits
• Gestation


  Period of development between conception and birth
• Gestational age


  Age of an unborn baby, usually dated from the first day of an expectant mother's last menstrual cycle
• Stages of prenatal development

  Germinal, embryonic, and fetal
• Growth and motor development occur from top down and from the center of the body outward, both before and after birth
• Germinal stage


  First 2 weeks of prenatal development, with rapid cell division, blastocyst formation, and implantation
• Embryonic stage


  Second stage of gestation (2 to 8 weeks), with rapid growth and development of major body systems and organs
• Spontaneous abortion


  Natural expulsion from the uterus of an embryo that cannot survive outside the womb, also called miscarriage
• Fetal stage


  Final stage of gestation (from 8 weeks to birth), with increased differentiation of body parts and greatly enlarged body size
• Prenatal development by month

  • First month: Embryo reaches 10,000 times greater size than zygote, with blood flow, heart beating, etc.
  • 7 weeks: Embryo becomes fetus with facial features, limbs, organ development
  • 3 months: Fingernails, toenails, eyelids, vocal cords, organ systems functioning
  • 4 months: Body catching up to head, umbilical cord growing, placenta fully developed, fetus kicking
  • 5 months: Signs of individual personality, sleep-wake patterns, gland development
  • 6 months: Fat pads, eyes complete, hearing and grip reflex
  • 7 months: Fully developed reflex patterns, crying, breathing, thumb sucking
  • 8 months: 18-20 inches long, 5-7 lbs, fat layer developing
  • 9 months: Boys tend to be longer and heavier, fat pads continue to form, more waste expelled