💀Anatomy and Physiology I Unit 28 – Development and Inheritance

Key Concepts

• Development is the process of change and growth from a single fertilized egg to a multicellular organism
• Embryonic development occurs in distinct stages (cleavage, gastrulation, neurulation, organogenesis) leading to the formation of a fetus
• Germ layers (ectoderm, mesoderm, endoderm) give rise to specific tissues and organs during embryonic development
• Cell differentiation is the process by which unspecialized cells become specialized for specific functions
  • Involves changes in gene expression and cell morphology
• Genetic inheritance follows Mendelian patterns (dominant, recessive, codominant, incomplete dominance) determined by alleles
• Developmental disorders can arise from genetic mutations, environmental factors, or a combination of both
• Understanding embryonic development and genetic inheritance has important clinical applications in diagnosing and treating congenital disorders

Embryonic Development Stages

• Cleavage is the rapid division of the zygote into smaller cells called blastomeres
  • Occurs without an increase in cell mass
  • Forms a solid ball of cells called a morula
• Gastrulation is the formation of the three primary germ layers (ectoderm, mesoderm, endoderm)
  • Involves cell migration and rearrangement
  • Establishes the basic body plan
• Neurulation is the formation of the neural tube, which gives rise to the central nervous system (brain and spinal cord)
  • Occurs through the folding and fusion of the neural plate
• Organogenesis is the development of specific organs and tissues from the germ layers
  • Involves cell differentiation, migration, and interactions
• Fetal development is the growth and maturation of the organs and systems formed during embryonic development
  • Occurs from the 9th week of gestation until birth

Germ Layers and Their Derivatives

• Ectoderm gives rise to the nervous system, skin, hair, nails, and tooth enamel
  • Forms the neural tube, neural crest cells, and epidermis
• Mesoderm gives rise to the musculoskeletal system, circulatory system, and connective tissues
  • Forms the notochord, somites, and intermediate mesoderm
  • Gives rise to bones, cartilage, muscles, blood, and kidneys
• Endoderm gives rise to the digestive system, respiratory system, and endocrine glands
  • Forms the primitive gut tube
  • Gives rise to the liver, pancreas, thyroid, and lungs

Cell Differentiation and Specialization

• Cell differentiation is the process by which unspecialized cells become specialized for specific functions
  • Involves changes in gene expression and cell morphology
• Stem cells are unspecialized cells that can give rise to multiple cell types
  • Can be embryonic (pluripotent) or adult (multipotent)
• Transcription factors are proteins that regulate gene expression and play a key role in cell differentiation
  • Bind to specific DNA sequences and promote or repress transcription
• Epigenetic modifications (DNA methylation, histone modifications) can alter gene expression without changing the DNA sequence
  • Play a role in cell differentiation and development
• Cell signaling (paracrine, endocrine, juxtacrine) is essential for coordinating cell differentiation and organ development

Genetic Inheritance Patterns

• Mendelian inheritance follows patterns determined by the segregation and independent assortment of alleles
  • Dominant alleles mask the expression of recessive alleles
  • Recessive alleles are expressed only when present in two copies (homozygous recessive)
• Codominance occurs when both alleles are expressed equally in the phenotype (ABO blood types)
• Incomplete dominance results in a blending of traits, with the heterozygous phenotype being intermediate between the homozygous phenotypes (snapdragon flower color)
• Sex-linked inheritance involves genes located on the sex chromosomes (X and Y)
  • X-linked recessive disorders (hemophilia, color blindness) are more common in males
• Multifactorial inheritance involves the interaction of multiple genes and environmental factors (height, skin color)

Developmental Disorders

• Congenital disorders are present at birth and can be caused by genetic mutations, chromosomal abnormalities, or environmental factors
• Down syndrome is caused by an extra copy of chromosome 21 (trisomy 21)
  • Results in intellectual disability, characteristic facial features, and increased risk of heart defects
• Neural tube defects (spina bifida, anencephaly) occur when the neural tube fails to close properly during neurulation
  • Can be prevented by folic acid supplementation during pregnancy
• Cleft lip and palate are caused by the failure of facial structures to fuse properly during development
  • Can be corrected with surgery and speech therapy
• Fetal alcohol syndrome is caused by maternal alcohol consumption during pregnancy
  • Results in growth deficiency, facial abnormalities, and neurodevelopmental problems

Clinical Applications

• Prenatal screening tests (ultrasound, maternal serum screening) can detect developmental disorders and congenital anomalies
  • Allows for early intervention and treatment
• Genetic testing (karyotyping, DNA sequencing) can diagnose genetic disorders and predict the risk of inheritance
  • Used for preimplantation genetic diagnosis in assisted reproductive technology
• Gene therapy involves the introduction of functional genes into cells to replace defective ones
  • Potential treatment for genetic disorders such as cystic fibrosis and sickle cell anemia
• Stem cell therapy uses pluripotent or multipotent stem cells to regenerate damaged tissues and organs
  • Promising for the treatment of neurodegenerative disorders, spinal cord injuries, and heart disease
• Teratology is the study of environmental factors that can cause developmental disorders
  • Identifies teratogens (alcohol, radiation, certain medications) and guides prevention strategies

Key Takeaways

• Embryonic development occurs in distinct stages (cleavage, gastrulation, neurulation, organogenesis) and gives rise to the fetus
• Germ layers (ectoderm, mesoderm, endoderm) give rise to specific tissues and organs during development
• Cell differentiation is the process by which unspecialized cells become specialized for specific functions, regulated by transcription factors and epigenetic modifications
• Genetic inheritance follows Mendelian patterns (dominant, recessive, codominant, incomplete dominance) determined by alleles
• Developmental disorders can be caused by genetic mutations, chromosomal abnormalities, or environmental factors (teratogens)
• Understanding embryonic development and genetic inheritance has important clinical applications in diagnosing and treating congenital disorders, such as through prenatal screening, genetic testing, gene therapy, and stem cell therapy