Form of New Life

Fertilization and Conception

  • Definition: Fertilization, or conception, is the process where sperm and ovum (male and female gametes) unite to form a zygote.
  • Zygote Formation: The zygote undergoes multiple cell divisions to develop into all the cells of a baby.
  • Ova in Females:
    • At birth, females have about 2 million immature ova in their ovaries.
    • Each ovum is contained in a follicle.
  • Ovulation:
    • Occurs approximately every 28 days until menopause.
    • Involves the release of a mature ovum from the follicle into the fallopian tube, assisted by cilia.
  • Sperm Production: Sperm are produced in the testes, averaging several hundred million per day.

Fertilization Process

  • Timing: Fertilization typically occurs in the fallopian tubes.
  • Post-Fertilization: If fertilization fails, both sperm and ovum die and are absorbed by the body.

Multiple Births

  • Dizygotic Twins (Fraternal):
    • Result from the fertilization of two separate eggs by two different sperm.
    • Genetically resemble typical siblings and may be the same or different sex.
    • Typically more common with multiple eggs being released.
  • Monozygotic Twins (Identical):
    • Arise from the division of a single fertilized zygote.
    • Genetically identical.
  • Factors Influencing Increased Multiple Births:
    1. Delayed childbearing.
    2. Rising usage of fertility drugs and assisted reproductive techniques, particularly among older women.

Mechanism of Heredity

  • DNA: Carries inherited instructions for life.
  • Genetic Code: Sequence of bases in DNA dictating protein formation.
  • Chromosomes: Coiled DNA structures containing genes.
  • Genes: Functional units of heredity located on chromosomes.
  • Human Genome: Complete genetic blueprint.
  • Mutation: Permanent genetic changes that can have harmful effects.

Gender and Sex Determination

  • At conception, 23 pairs of chromosomes (46 total) form where:
    • 22 pairs are autosomes (non-sex-related).
    • The 23rd pair are sex chromosomes (XX for females, XY for males).
  • An ovum contributes an X chromosome; sperm may contribute either an X or a Y.
  • The SRY gene on the Y chromosome determines maleness.
    • XX: genetic female.
    • XY: genetic male.

Dominant and Recessive Inheritance

  • Alleles: Different forms of a gene impacting the same trait.
  • Homozygous: Two identical alleles for a trait.
  • Heterozygous: Two different alleles for a trait.
    • Dominant Inheritance: Only dominant allele expressed in phenotype.
    • Recessive Inheritance: Non-dominant trait expressed only with identical recessive alleles.

Genotypes and Phenotypes

  • Phenotype: Observable traits.
  • Genotype: Genetic makeup (expressed and unexpressed traits).
  • Example of Multifactorial Transmission: Type 2 Diabetes, influenced by both genetic predispositions and environmental factors.

Epigenesis

  • Definition: Mechanisms turning genes on/off affecting functions of body cells.
  • Epigenetic Tags: Chemical modifications impacting gene expression without altering DNA sequence.
  • Influences on Epigenetics: Nutrition, stress, lifestyle, can lead to diseases like cancer.

Birth Defects

  • Common Issues:
    • Alpha-1 antitrypsin deficiency, Cystic fibrosis, Duchenne muscular dystrophy, etc.
  • Characteristics and who is at risk are specified along with possible interventions.

Neural-Tube Defects

  • Anencephaly: Absence of brain tissue, usually fatal.
  • Spina bifida: Incomplete spinal canal closure, can lead to severe complications.
  • Prevention: Special diets or surgery may mitigate some effects.

Environmental Influences on Development

  • Maternal Nutrition and Teratogens:
    • Importance of folic acid, iron, calcium, iodine for fetal development.
    • Exposure Risks: Alcohol, tobacco, drugs can lead to significant birth defects.

Prenatal Stages of Development

  • Germinal, Embryonic, and Fetal Stages: Characterized by critical growth, organ development, hormonal environment, and physical changes at each stage.
    • Specific milestones listed by weeks of gestation, including sensory development.

Postnatal Influences

  • Breastfeeding: Provides essential nutrients and immune support.
  • Caregiving: Influences on emotional and cognitive development.
  • Environmental Interaction: What a child is exposed to continues shaping development post-birth.