Hereditary and Environmental Influences on Development

HEREDITARY AND ENVIRONMENTAL INFLUENCES ON DEVELOPMENT

Introduction to DNA and Genetic Structure

  • Definition of DNA:

    • DNA (Deoxyribonucleic Acid) is the hereditary material in humans and nearly all other organisms.

    • DNA is structured in a double helix formation comprising nucleotides that consist of a sugar, phosphate group, and a nitrogenous base.

Gene and Chromosome Structure

  1. Structure and Function of Normal Human Genes and Chromosomes:

    • Gene Structure:

      • Genes are segments of DNA that contain the code for proteins, which perform most life functions.

      • Each human cell contains approximately 20,000 to 25,000 genes.

    • Chromosome Structure:

      • Humans typically have 46 chromosomes, organized into 23 pairs.

      • Each chromosome consists of long strands of DNA tightly coiled around proteins called histones.

      • Chromosomes are located within the nucleus of the cell.

Review of Chromosome Structure

  • Chromosomes Represented Visually:

    • Chromosome Numbering and Arrangement:

      • Chromosomes are numbered from 1 to 22, with an additional pair being the sex chromosomes (XX for female, XY for male).

      • Example representation:

      • Normal cell with chromosomes numbered (1-22) and X/Y indications for sex chromosomes.

Chromosomal Abnormalities

  1. Explanation of Chromosomal Abnormalities:

    • Types of Chromosomal Abnormalities:

      • Numeric Abnormalities: Changes in the number of chromosomes.

        • Trisomy: Presence of an extra chromosome (e.g., Trisomy 21 causes Down syndrome).

        • Monosomy: Absent of one chromosome in a pair (e.g., Turner syndrome).

        • Polyploidy: Presence of more than two homologous sets of chromosomes.

      • Structural Abnormalities: Changes in the structure of a chromosome.

        • Turner’s Syndrome: A chromosomal condition affecting development in females.

Multifactorial Birth Defects and Disorders

  1. Multifactorial Birth Defects/Disorders:

    • Most Common Multifactorial Disorders:

      • Heart defects.

      • Neural tube defects (e.g., spina bifida).

      • Cleft lip and cleft palate.

      • Pyloric stenosis: A condition that blocks food from entering the small intestine.

    • Understanding Multifactorial Disorders:

      • These disorders arise from a combination of genetic predispositions and environmental influences.

Environmental Influences on Development

  1. Environmental Influences:

    • Definition of Teratogens:

      • Teratogens are agents or factors that cause malformation during embryonic or fetal development. They increase the risk of birth defects.

    • Examples of Teratogens:

      • Maternal infections (e.g., rubella).

      • Drug use (e.g., alcohol, smoking, illicit drugs).

      • Exposure to pollutants and chemicals (e.g., heavy metals, pesticides).

      • Ionizing radiation (e.g., X-rays).

      • Maternal hyperthermia (elevated body temperature can harm fetal development).

      • Maternal disorders such as diabetes or hypertension can also pose risks to fetal health.

Strategies for Avoiding Environmental Exposures

  1. Avoiding and Reducing Teratogenic Effects:

    • Key Strategies for Reducing Exposure:

      • Prenatal care and regular check-ups during pregnancy.

      • Immunizations to prevent maternal infections.

      • Avoidance of harmful substances (drugs, alcohol, tobacco).

      • Minimizing exposure to potentially harmful pollutants and chemicals.

      • Management of maternal health conditions to ensure stability before and during pregnancy.

    • Implications of Avoiding Exposure:

      • Understanding the dangers of various environmental factors allows prospective parents to take necessary precautions that can significantly reduce the risks of birth defects and promote overall fetal health.