Genetic Code and Inheritance Quiz
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Questions and Answers

Which part of the somite contributes to the formation of muscle tissue?

  • Dermatome
  • Rhombomere
  • Myotome (correct)
  • Sclerotome

    • What signaling molecules are known to induce neural crest cell differentiation?

  • BMP and TGF-beta
  • IL-6 and TNF-alpha
  • Wnt and FGF (correct)
  • Shh and Notch

    • Which somite part develops into connective tissue of the skin?

  • Dermatome (correct)
  • Sclerotome
  • Myotome
  • Notochord

    • Which of the following structures forms the face during embryonic development?

    <p>Midbrain and rhombomeres 1 &amp; 2</p> Signup and view all the answers

    What is a significant role of neural crest cells during embryonic development?

    <p>Contributing to craniofacial skeleton and teeth</p> Signup and view all the answers

    Which of the following correctly describes the structure of DNA?

    <p>Double helix wrapped around histones with strands running in opposite directions</p> Signup and view all the answers

    What is the role of RNA polymerase during transcription?

    <p>To catalyze the synthesis of RNA from a DNA template</p> Signup and view all the answers

    Which of these statements accurately defines polygenic inheritance?

    <p>It involves multiple genes contributing to a single trait</p> Signup and view all the answers

    Which of the following correctly distinguishes between genotype and phenotype?

    <p>Genotype describes the genetic information while phenotype describes the physical characteristics</p> Signup and view all the answers

    In the context of Mendelian genetics, what does it mean for an organism to be homozygous?

    <p>Possessing two identical alleles for a specific gene</p> Signup and view all the answers

    Which of the following is an example of x-linked inheritance?

    <p>Color blindness</p> Signup and view all the answers

    Which of the following statements about multifactorial traits is true?

    <p>They are influenced by multiple genes and environmental factors</p> Signup and view all the answers

    What distinguishes autosomal traits from x-linked traits?

    <p>Autosomal traits do not involve the X chromosome unlike x-linked traits</p> Signup and view all the answers

    What distinguishes somatic mutations from germ line mutations?

    <p>Somatic mutations occur in somatic cells and are not passed to offspring.</p> Signup and view all the answers

    Which type of mutation can lead to a frameshift effect?

    <p>Deletion mutation</p> Signup and view all the answers

    What is the primary role of natural killer cells in the innate immune system?

    <p>To activate upon seeing infected cells without inhibiting receptors.</p> Signup and view all the answers

    What does methylation in the context of epigenetics specifically refer to?

    <p>The addition of a methyl group to a DNA base.</p> Signup and view all the answers

    How do cytokines function in the innate immune system?

    <p>They signal other cells for proliferation and differentiation.</p> Signup and view all the answers

    Which best describes the primary distinction between innate and adaptive immunity?

    <p>Innate immunity is faster, acting before microbial encounter.</p> Signup and view all the answers

    Which of the following mutations is categorized as a translocation mutation?

    <p>A segment of one chromosome moves to another chromosome.</p> Signup and view all the answers

    What outcome can silent mutations yield?

    <p>They change the amino acid sequence without changing the protein's function.</p> Signup and view all the answers

    Which type of immune cell is primarily responsible for the initial response to infections?

    <p>Macrophages</p> Signup and view all the answers

    What is one function of cytokines in the adaptive immune system?

    <p>They regulate immune cells and molecules.</p> Signup and view all the answers

    Which component is primarily responsible for opsonization in the adaptive immune response?

    <p>Complement proteins</p> Signup and view all the answers

    Which statement about TNFα is true?

    <p>It induces apoptosis and activates neutrophils.</p> Signup and view all the answers

    What role do commensal microbes play in oral health?

    <p>They outcompete pathogens for resources.</p> Signup and view all the answers

    Which structure is primarily responsible for providing a mechanical barrier to microbial entry?

    <p>Stratified squamous epithelium</p> Signup and view all the answers

    What is the primary type of cell found in the connective tissue layer known as lamina propria?

    <p>Fibroblasts</p> Signup and view all the answers

    Which of the following best describes the structural arrangement of keratin pearls in oral cancer?

    <p>A lack of defined layers, with differentiation occurring in inappropriate locations.</p> Signup and view all the answers

    Which component of the immune system has a primary role in displaying antigens to T cells?

    <p>Macrophages</p> Signup and view all the answers

    What is the consequence of excess inflammatory cytokines during an immune response?

    <p>Potential tissue damage.</p> Signup and view all the answers

    Which type of tissue is primarily involved in the absorption of nutrients during the immune response?

    <p>Epithelial tissue</p> Signup and view all the answers

    Which cell type is primarily responsible for releasing IL-12 to activate NK cells?

    <p>Macrophages</p> Signup and view all the answers

    What is the role of perforin in the immune response?

    <p>To create openings in infected cells</p> Signup and view all the answers

    What distinguishes innate lymphoid cells from T cells?

    <p>They respond to cytokines instead of antigens.</p> Signup and view all the answers

    During the extravasation process, what is the first step that occurs at the site of infection?

    <p>Secretion of cytokines and chemokines</p> Signup and view all the answers

    What function do basophils serve in the immune system?

    <p>Releasing histamine during allergic reactions</p> Signup and view all the answers

    What is a defining characteristic of the complement system in innate immunity?

    <p>It plays a role in tagging pathogens for destruction.</p> Signup and view all the answers

    In addition to macrophages, which cell type is involved in the response against intracellular infections?

    <p>CD8 T cells</p> Signup and view all the answers

    Which of the following stages is NOT part of prenatal development?

    <p>Differentiation of somatic cells</p> Signup and view all the answers

    What is a major function of Eosinophils?

    <p>Response to parasitic infections</p> Signup and view all the answers

    What initiates the process of induction during embryonic development?

    <p>Patterning and signaling events</p> Signup and view all the answers

    What is the main difference between monogenic and polygenic inheritance?

    <p>Monogenic inheritance is determined by one gene, while polygenic involves multiple genes.</p> Signup and view all the answers

    Which of the following correctly describes the base pairing in DNA and RNA?

    <p>Adenine pairs with Thymine in DNA and Uracil in RNA.</p> Signup and view all the answers

    What defines a heterozygous genotype?

    <p>Having alleles from both parents that are different for a specific gene.</p> Signup and view all the answers

    In what way do multifactorial traits differ from polygenic traits?

    <p>Multifactorial traits involve both genetic and environmental factors.</p> Signup and view all the answers

    Which statement accurately describes the composition of a DNA molecule?

    <p>DNA is a double helix with an antiparallel arrangement of strands.</p> Signup and view all the answers

    What role do ribosomes play in the translation process?

    <p>They facilitate the assembly of amino acids into proteins.</p> Signup and view all the answers

    Which of the following best describes an allele?

    <p>A different form of a gene found at the same locus on a chromosome.</p> Signup and view all the answers

    What characteristic distinguishes x-linked traits from autosomal traits?

    <p>X-linked traits are carried on the X chromosomes.</p> Signup and view all the answers

    What is the primary role of cytokines produced by innate lymphoid cells?

    <p>To influence the activity of other immune cells</p> Signup and view all the answers

    Which step in the process of extravasation involves increased integrin affinity?

    <p>Increase in integrin affinity</p> Signup and view all the answers

    What effector mechanism is primarily utilized by Natural Killer (NK) cells to eliminate infected cells?

    <p>Release of perforin and granzymes</p> Signup and view all the answers

    Which component of the innate immune system is specifically designed to recognize fungal pathogens?

    <p>C-type lectin receptors (CLR)</p> Signup and view all the answers

    Which of the following stages of prenatal development is characterized by morphogenesis?

    <p>Stage 2 (4-8 weeks)</p> Signup and view all the answers

    Which cell type is activated by macrophages releasing IL-12 in response to infection?

    <p>Natural Killer (NK) cells</p> Signup and view all the answers

    During which phase of the immune response are chemical signals crucial for the recruitment of leukocytes?

    <p>Inflammatory phase</p> Signup and view all the answers

    What is the consequence of excessive activation of the innate immune system?

    <p>Damage to host tissue leading to pathology</p> Signup and view all the answers

    What type of pathogen is primarily recognized by RIG-I-like receptors (RLR)?

    <p>Viruses</p> Signup and view all the answers

    What process initiates differentiation during embryonic development?

    <p>Induction</p> Signup and view all the answers

    Which of the following accurately describes a characteristic of Treacher Collins' syndrome?

    <p>It is linked to a mutation in the Tcof1 gene.</p> Signup and view all the answers

    What is the primary consequence of decreased neural crest cell migration into the first pharyngeal arch during embryonic development?

    <p>Altered facial structure leading to anomalies.</p> Signup and view all the answers

    Fetal Alcohol Syndrome (FAS) is associated with excessive alcohol consumption during pregnancy. What is a critical factor for the development of FAS?

    <p>Timing of fetal exposure to alcohol.</p> Signup and view all the answers

    Which of the following factors is NOT associated with congenital defects?

    <p>Emotional stress experienced by the mother.</p> Signup and view all the answers

    In Pierre Robin's sequence, what is a primary characteristic feature?

    <p>Micrognathia.</p> Signup and view all the answers

    What is the role of the myotome within each somite?

    <p>Originates muscles</p> Signup and view all the answers

    Which component of the somite is responsible for forming adjacent vertebrae?

    <p>Sclerotome</p> Signup and view all the answers

    Which statement about rhombomeres is true?

    <p>Play a role in forming the hindbrain and face</p> Signup and view all the answers

    What signals induce the differentiation of neural crest cells?

    <p>Wnt and FGF</p> Signup and view all the answers

    Neural crest cells are primarily responsible for which aspect of craniofacial development?

    <p>Migration and formation of connective tissues</p> Signup and view all the answers

    During which weeks of embryonic development do neural crest cells primarily manifest?

    <p>3-4 weeks</p> Signup and view all the answers

    What is the primary function of signalling molecules like Wnt and FGF in the context of neural crest cells?

    <p>To induce epithelial-mesenchymal transformation</p> Signup and view all the answers

    What does the dermatome of a somite develop into?

    <p>Connective tissue of skin</p> Signup and view all the answers

    Which formation is NOT associated with the midbrain and rhombomeres?

    <p>Formation of forebrain structures</p> Signup and view all the answers

    Which transcription factor family is involved in determining the competence of neural crest cells?

    <p>Snail zinc-finger transcription factor family</p> Signup and view all the answers

    What physiological change occurs to the respiratory system during pregnancy?

    <p>Diaphragm moves upwards, reducing functional residual capacity</p> Signup and view all the answers

    Which statement accurately describes the role of homeobox genes in development?

    <p>They provide developmental signals critical in the formation of embryonic structures.</p> Signup and view all the answers

    What is the primary outcome of gastrulation in embryonic development?

    <p>Development of the trilaminar embryo consisting of three germ layers.</p> Signup and view all the answers

    Which statement about Turner syndrome is accurate?

    <p>It results from the partial or complete absence of an X chromosome.</p> Signup and view all the answers

    What process is indicated by the term 'epigenetics'?

    <p>Alterations in gene activity without changes to the DNA sequence.</p> Signup and view all the answers

    Which layer of the trilaminar embryo forms the connective tissues and muscles?

    <p>Mesoderm</p> Signup and view all the answers

    What defines the 'primitive streak' during embryonic development?

    <p>An indication of body axis establishment and cellular migration.</p> Signup and view all the answers

    Which of the following is a significant consequence of DNA hypermethylation?

    <p>Decreased gene transcription and silencing of genes.</p> Signup and view all the answers

    What is the typical age range for the completion of permanent teeth development?

    <p>7-21 years</p> Signup and view all the answers

    In terms of placental function, what role does hCG play during early pregnancy?

    <p>It maintains the corpus luteum and supports early pregnancy.</p> Signup and view all the answers

    Study Notes

    Genetic Code

    • Adenine (A), Guanine (G) are purines
    • Cytosine (C), Thymine (T), Uracil (U) are pyrimidines
    • Adenine pairs with Thymine (U in RNA)
    • Guanine pairs with Cytosine
    • DNA is a double helix with strands running in opposite directions
    • DNA is wrapped around histones
    • RNA polymerase creates a copy of DNA during transcription
    • Transcription uses Uracil (U) instead of Thymine (T)
    • Translation occurs at the ribosome to create proteins
    • Codons, three bases, code for a single amino acid
    • Genome refers to the complete set of DNA found within chromosomes in the nucleus
    • Red blood cells lack a genome
    • Different genes are expressed in different cells to produce specific proteins for cell function

    Inheritance

    • Monogenic Inheritance involves one set of alleles/specific gene
    • Polygenic Inheritance involves multiple genes, e.g. skin color
    • Multifactorial/complex traits are influenced by multiple genes and environmental factors, e.g. height
    • Genotype describes the genetic information for a specific trait
    • Phenotype describes the physical characteristic of a trait
    • Allele is a different form of a gene found at a specific location on a chromosome
    • Homozygous describes having two identical alleles, e.g. HH or hh
    • Heterozygous describes having two different alleles, e.g. Hh

    Patterns of Inheritance

    • Autosomal traits are carried on any chromosome other than X and Y
    • Dominant or recessive alleles can affect traits
    • X-linked traits are carried on the X chromosome, e.g. color blindness or hemophilia A
    • Polygenic traits show continuous variation, e.g. height
    • Genetic risk factors contribute to complex diseases such as cancers or Type 2 diabetes

    Mutations

    • Mutation involves a change in the DNA sequence
    • Germline mutations occur in gametes and can be passed down to offspring
    • Somatic mutations occur in somatic cells and cannot be passed down to offspring
    • Substitution mutation alters a single base pair within the DNA sequence, which can lead to silent, nonsense, or missense mutations
    • Deletion mutation removes a section of DNA, while insertion mutation adds a section, causing a frameshift
    • Translocation mutation moves a section of a chromosome, altering the chromosome structure

    Epigenetics

    • Epigenetics refers to heritable changes in gene expression that are not caused by alterations in DNA sequence
    • Epigenetics involves modifying genes to alter their expression
    • Methylation is an epigenetic mechanism that adds a methyl group to a DNA base, altering gene expression
    • Environmental factors can cause epigenetic changes.

    Innate Immunity

    • Innate Immunity is the first line of defense against pathogens
    • Innate Immunity is older than adaptive immunity, existing prior to microbial encounter
    • Components of Innate Immunity include barriers, cytokines, circulating effector cells, and circulating effector proteins

    Barriers:

    • Skin
    • Mucous membranes
    • Epithelial layers
    • Enzymes
    • pH
    • Commensal microbes

    Circulating Effector Cells:

    • Neutrophils
    • Dendritic Cells
    • Macrophages
    • Natural Killer Cells
    • Innate Lymphoid Cells
    • Mast cells, eosinophils, and basophils

    Circulating Effector Proteins:

    • **Complement System **: this group of proteins work synergistically to enhance the immune response

    Neutrophils, Dendritic Cells, and Macrophages:

    • First responders to infection
    • Recognize and signal infection
    • Clear debris from infected tissue
    • Phagocytosis

    MHC:

    • MHC II is an antigen-presenting cell that displays extracellular antigens
    • MHC I is an antigen-presenting cell that displays intracellular antigens

    Natural Killer (NK) Cells:

    • Circulate with inhibitory receptors
    • Activate when encountering infected cells without an inhibitory receptor
    • Signal other NK cells
    • Kill infected cells
    • No Class I MHC = kill
    • 5-10% of lymph in blood and spleen
    • Effector functions:
    • Perforin: creates openings in cell membranes
    • Granzyme: enters cells and triggers apoptosis

    Macrophage-NK Cell Interactions:

    • Macrophages control intracellular infections until adaptive immunity takes over
    • Infected macrophages release IL-12
    • IL-12 activates NK cells - NK cells release IFN-ϒ
    • IFN-ϒ mediates macrophage activation, differentiation, and killing of bacteria
    • IL-12 increases NK cell population contributing to inflammation
    • NK cells secrete IFN-ϒ

    Innate Lymphoid Cells:

    • Cytokine-producing lymphocytes
    • Respond to cytokines rather than antigens
    • Third largest lymphocyte population
    • Defined by transcription factors

    Mast Cells, Eosinophils, and Basophils:

    • Mast cells
    • Release histamine
    • Increase vascular permeability and smooth muscle contraction
    • Important in allergy responses
    • Tissue resident
    • Basophils
    • Release histamine
    • Circulating
    • Important in parasitic infections
    • Eosinophils
    • Release inflammatory molecules
    • Respond to parasites

    Inflammation

    • Protective mechanism in response to infection
    • Recruits leukocytes
    • Extravasates plasma proteins to the site of infection
    • Activates leukocytes to eliminate infection

    Extravasation:

    1. Secretion of cytokines and chemokines at the site of infection
    2. Selectin-mediated rolling of leukocytes
    3. Increased affinity of integrins
    4. Integrin-mediated attachment to endothelium
    5. Transmigration through the endothelium
    6. Migration to the site of infection

    Complement System:

    • Enhances the innate immune response

    Innate Immune Recognition:

    • Recognizes microbial pathogens but not host cells
    • Four major classes of pattern recognition receptors (PRRs)
    • Toll-like receptors (TLRs): recognize bacteria and viruses
    • C-type lectin receptors (CLRs): recognize fungi
    • Nod-like receptors (NLRs): recognize bacteria and cellular damage
    • RIG-I-like receptors (RLRs): recognize viruses

    Key Effector Mechanisms of Innate Immunity:

    • Phagocytosis
    • Extracellular killing by complement
    • NK cell killing
    • Inflammation

    Innate Immunity and Adaptive Immunity:

    • Innate immunity orchestrates the adaptive immune response by:
    • Presenting antigens to adaptive immune cells
    • Producing cytokines that activate adaptive immune cells

    Components of Innate Immunity in the Oral Cavity:

    • Saliva: contains antimicrobial factors such as lysozyme, lactoferrin, and antibodies
    • Oral Mucosa: acts as a physical barrier and houses immune cells such as macrophages, neutrophils, and dendritic cells

    Embryonic Development

    • Somatic cells have 46 chromosomes
    • Germ cells contain 23 chromosomes
    • Fertilization is the fusion of male (sperm) and female (ova) gametes
    • Zygote is the fertilized cell
    • Diploid is the complete number of chromosomes in somatic cells
    • Haploid is half the number of chromosomes in gametes
    • Mitosis produces identical daughter cells
    • Meiosis produces daughter cells with half the number of chromosomes

    Prenatal Development:

    • Stage 1 (0-4 weeks): Cellular proliferation, migration, and differentiation
    • Stage 2: Morphogenesis
    • Stage 3: Growth and maturation

    Induction, Competence, and Differentiation:

    • Induction is the process that initiates differentiation
    • Competence is the ability of a cell to respond to inductive signals
    • Differentiation is the process of a cell becoming specialized

    Oral Disease:

    • Caries involves tooth decay
    • Periodontal disease involves gum disease
    • Oral cancer involves cancer of the oral cavity

    Oral Tissues:

    • Oral mucosa: lines the mouth and is composed of stratified squamous epithelium
    • Basal layer: the innermost layer responsible for cell renewal
    • Connective tissue (lamina propria): contains collagen and fibroblasts
    • Lumen of blood vessel: provides blood supply
    • Salivary gland: produces saliva
    • Enamel: the outermost layer of the tooth, composed of enamel rods, lamellae, and striae of Retzius
    • Dentin: the underlying layer of the tooth that contains dentinal tubules
    • Pulp: the innermost layer of the tooth that contains blood vessels and nerves
    • Periodontal ligament (PDL): fibrous tissue that connects the tooth to the bone
    • Cementum: the layer that covers the tooth root and attaches to the PDL
    • Bone: the supporting structure of the tooth, composed of osteoblasts and osteoclasts
    • Epithelial rests: rests of the dental lamina found within the PDL and can contribute to the formation of cysts and tumors

    Tooth Development:

    • Outer enamel epithelium: the outermost layer of the enamel organ
    • Stellate reticulum: loosely arranged cells that maintain the shape of the enamel organ
    • Dental papilla: the core of the tooth bud that will develop into the dentin and pulp
    • Dental lamina: a band of epithelial cells that gives rise to the enamel organ
    • Inner enamel epithelium: the layer of cells within the enamel organ that secretes enamel

    Adaptive Immunity

    • Adaptive Immune System is the branch of immunity that is a specific response to pathogens
    • Adaptive Immune Cells:
    • T cells are responsible for cell-mediated immunity
    • B cells are responsible for humoral immunity, producing antibodies
    • Adaptive Immune Response involves:
    • Specificity
    • Memory
    • Tolerance
    • Components of Adaptive Immunity:
    • T lymphocytes (T cells)
    • B lymphocytes (B cells)
    • Antigen-presenting cells (APCs)
    • Antibodies
    • Cytokines

    Key Adaptive Immune Cells:

    • T cells:
    • Helper T cells (Th cells): activate other immune cells
    • Cytotoxic T cells (Tc cells): directly kill infected cells
    • Regulatory T cells (Treg cells): suppress immune responses
    • B cells:
    • Plasma cells: produce antibodies
    • Memory B cells: provide long-term immunity
    • Antigen-Presenting Cells (APCs) :
    • Macrophages
    • Dendritic cells
    • B cells
    • Present antigens to T cells

    Antibodies:

    • Proteins that bind to specific antigens
    • Neutralize pathogens by blocking their ability to infect cells
    • Opsonize pathogens by making them more susceptible to phagocytosis
    • Activate complement

    Cytokines:

    • Signaling molecules that regulate immune responses

    Key Cytokines:

    • TNFα: a major inflammatory mediator
    • IL-1β: a key inflammatory mediator
    • IFNγ: promotes anti-viral responses
    • IL-4: promotes B cell development and antibody production

    Embryonic Development:

    • Neural crest cells: a multipotent cell population that gives rise to a variety of tissues in the head and neck, including the teeth
    • Ectomesenchyme: embryonic connective tissue derived from neural crest cells
    • The neural crest: is a group of cells located at the dorsal margin of the closing neural tube, playing a crucial role in the development of the craniofacial skeleton, teeth, and other tissues
    • Neural crest cells undergo an epithelial-mesenchymal transformation, migrating extensively to form various tissues.
    • Somitomeres form head muscles.
    • Somites give rise to the vertebrae and skeletal muscles.
    • Rhombomeres contribute to the formation of the face and pharyngeal structures.

    Tooth Development:

    • Tooth development is a complex process involving a series of interactions between epithelial and mesenchymal tissues.
    • The dental lamina is a band of epithelial cells that gives rise to the enamel organ.
    • The enamel organ forms the enamel of the tooth.
    • The dental papilla forms the dentin and pulp of the tooth.
    • The dental follicle forms the cementum, periodontal ligament, and alveolar bone of the tooth.
    • Enamel is the hardest tissue in the body.
    • Dentin is a calcified tissue that forms the bulk of the tooth.
    • Pulp is the soft tissue that contains blood vessels, nerves, and lymphatic vessels.
    • Cementum is a thin layer of calcified tissue that covers the tooth root.
    • The periodontal ligament is a fibrous tissue that anchors the tooth to the bone.
    • Alveolar bone supports the tooth.

    Genetics

    • DNA Structure: Double helix, strands run in opposite directions, wrapped around histones.
    • DNA Strands: Run in a 5' to 3' direction.
    • Nucleotide Bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T) in DNA and Uracil (U) in RNA.
    • Base Pairing: A-T (or U in RNA) and G-C.
    • Transcription: Copying DNA into RNA using RNA polymerase.
    • Translation: Converting RNA into proteins at the ribosome.
    • Codons: Groups of three bases that code for a single amino acid.
    • Genome: Complete set of DNA stored in chromosomes within the nucleus.

    Patterns of Inheritance

    • Monogenic Inheritance: A trait controlled by a single gene.
    • Polygenic Inheritance: A trait controlled by multiple genes.
    • Multifactorial Traits: Influenced by multiple genes and environmental factors.
    • Genotype: Genetic makeup.
    • Phenotype: Observable physical characteristics.
    • Allele: Different forms of a gene found at the same locus.
    • Homozygous: Having two identical alleles for a trait.
    • Heterozygous: Having two different alleles for a trait.

    Autosomal and X-Linked Inheritance

    • Autosomal Traits: Genes located on chromosomes other than X or Y.
    • X-Linked Traits: Genes located on the X chromosome.
    • Dominant Traits: One copy of the dominant allele is sufficient to express the trait.
    • Recessive Traits: Two copies of the recessive allele are needed to express the trait.

    Embryonic Development

    • Germ cells: Contain half the number of chromosomes compared to somatic cells.
    • Fertilization: Fusion of male and female germ cells (sperm and egg) resulting in a zygote.
    • Somatic Cells: Have a complete set of chromosomes (diploid).
    • Gametes: Have half the number of chromosomes (haploid).
    • Mitosis: Cell division in somatic cells, resulting in two identical daughter cells.
    • Meiosis: Cell division in reproductive cells, resulting in four daughter cells with half the number of chromosomes.

    Stages of Prenatal Development

    • Stage 1 (0-4 weeks): Cellular proliferation and migration, some differentiation.
    • Stage 2: Morphogenesis (formation of shape) and complex embryologic processes.
    • Stage 3: Growth and maturation.

    Induction, Competence and Differentiation

    • Induction: Process that initiates differentiation.
    • Competence: Ability of a cell to respond to inductions.
    • Differentiation: Process by which cells become specialized.

    Innate Immunity

    • Recognize microbial pathogens: Not somatic cells.
    • Key Recognition Classes: TLRs, CLRs, NLRs, RLRs.
    • Effector Mechanisms: Phagocytosis, inflammation, complement system activation.

    Inflammation

    • Protective response: Recruiting leukocytes and plasma proteins to infection site.
    • Extravasation: Process of leukocytes moving from blood vessels to infection site.
    • Components: Cytokines, chemokines, selectins, integrins.

    Adaptive Immunity

    • Orchestrates the adaptive immune response: Triggered by innate immune system, leading to antigen-specific adaptive immune responses.

    Oral Cavity Innate Immunity

    • Components: Saliva, epithelial cells, leukocytes, and other innate immune cells.### Gametogenesis, Blastocyst formation and Gastrulation

    • Fertilized egg undergoes rapid divisions, forming a ball of cells called a morula

    • Fluid builds up in the morula, and cells realign to form a blastocyst (blastula)

    • The embryoblast differentiates into the 2-layered bilaminar disc

    • Ectoderm (dorsal) forms the amniotic cavity

    • Endoderm (ventral) forms the secondary yolk sac

    Trilaminar Embryo Disc

    • Bilaminar disc (ectoderm + endoderm) converts into the trilaminar embryo disc
    • Primitive streak forms
    • Cell shape changes, rearrangement, movement and alterations in adhesive properties occur

    Gastrulation

    • Blastula transitions into gastrula
    • Ectodermal and endodermal cells slightly enlarge
    • The axis of the embryo is established after 2 weeks
    • The head end (rostral) is the cranial/prochordal end
    • The tail (caudal) end is the cecal plate
    • Cells migrate through the primitive streak and change shape, traveling laterally and cephalically
    • Epiblast cells break off and travel to form 3 layers; endoderm, mesoderm, and ectoderm
    • Endoderm forms by epiblast cells migrating from the primitive pit, displacing the hypoblast
    • Mesoderm lies between the endoderm and ectoderm
    • Ectoderm remains as epiblast cells
    • These cells are responsible for forming different tissues in the fetus

    Tissue Formation

    • Ectoderm: forms epidermis of skin, cornea and lens of the eye, nervous system
    • Mesoderm: forms notochord, musculoskeletal (MSK) system, muscle of stomach and intestines, circulatory system, respiratory system, and the outer lining of the gut
    • Endoderm: forms liver, pancreas, lining of the urethra, bladder and reproductive system, and the epithelial lining of the digestive and respiratory tracts

    Chromosomal Abnormalities

    • Meiosis malfunction can lead to an abnormal number of chromosomes, resulting in congenital abnormalities, especially in the head and neck region, including teeth.
    • Trisomy 21 (Down Syndrome): occurs when a 24-chromosome gamete fuses with a normal gamete, resulting in 47 chromosomes and an extra chromosome (trisomic).
      • Facial clefts, a shortened palate, protruding and fissured tongue, and delayed tooth eruption can occur
    • Turner Syndrome: the most common chromosomal disorder in females, with a partial or complete missing X chromosome (monosomy).
      • Dysmorphic stigmata, shortness in stature, sexual infantilism, as well as renal, cardiac, skeletal, endocrine, and metabolic abnormalities can be observed.

    Single Gene Malfunctions

    • Approximately 10% of mutations are caused by single gene malfunction
    • Autosomal dominant: achondroplasia, cleidocranial dysostosis, osteogenesis imperfecta, and dentinogenesis imperfecta
    • Autosomal recessive: chondroecto dysplasia, cystic fibrosis

    Epigenetics

    • Epigenetics refers to the study of heritable changes in gene expression that occur without alterations in the underlying DNA sequence.
    • DNA methylation: involves the addition of a methyl group to cytosines via covalent modification. It typically occurs in CpG regions, which are clusters found in promoter regions.
      • Hypermethylation decreases gene transcription, while hypomethylation increases gene transcription.
    • Histone modification: involves modifying positively charged nuclear proteins that DNA wraps around. This affects the activity of promoters, thereby regulating transcription.
    • Non-coding RNA: a cluster of RNA molecules that do not encode functional proteins. They can regulate gene expression and chromosomes to control cell differentiation.
    • Genetics determines the inheritance of traits and disorders, while epigenetics determines which genes are activated through chemical modifications to DNA and proteins, influencing when and where genes are active.

    Physiological Changes in Pregnancy

    • Basal metabolic rate (BMR): increases
    • Cardiac Output: increases
    • Blood Volume: increases
    • Oxygen utilisation: increases
    • Ventilation: increases
    • Renal tubule reabsorption: increases
    • Glomerular filtration rate (GFR): increases
    • Lumbar lordosis: increases
    • Symphysis pubis diastasis: can occur, leading to back pain

    Weight Gain in Pregnancy

    • Average fetus: contributes significantly to weight gain
    • Embryonic fluid: adds to weight increase
    • Uterus: enlarges, adding weight
    • Breasts: increase in size, contributing to weight gain
    • Body fluid: volume increases
    • Fat accumulation: occurs to support the pregnancy and provide reserves

    First Trimester Symptoms

    • 80% of miscarriages occur in the first trimester (10-15% of pregnancies).
    • Morning sickness: nausea (50-70%) and vomiting (40-50%)
    • Sensitive/sore breasts
    • Frequent urination
    • Constipation
    • Changing emotions
    • Hyperemesis gravidarum: severe nausea and vomiting, leading to dehydration and weight loss

    Second Trimester Symptoms

    • Some nausea and vomiting
    • Frequent urination
    • Insomnia
    • Indigestion and muscle cramping
    • Feel fetal movements (18-20 weeks)
    • Pain with stretched uterus
    • Leukorrhea: vaginal discharge

    Third Trimester Symptoms

    • Breathlessness: pressure on diaphragm
    • Edema: swollen ankles and toes, caused by vena cava restriction
    • Frequent urination
    • Itchy skin
    • Braxton Hicks contractions: practice contractions and nesting instincts
    • Water breaks: rupture of amniotic sac

    Hormonal Changes in Pregnancy

    • Human chorionic gonadotropin (hCG): supports corpus luteum, a temporary organ in the ovary in early pregnancy, which is detected by pregnancy tests. It peaks at 7-12 weeks, after which the placenta takes over.
    • Progesterone: establishes the placenta, promotes blood vessel formation in the womb, strengthens pelvic wall muscles for labor, and decreases lactation.
    • Estrogen: increases uterine growth, maintains uterine lining, supports fetal organ development (lungs and liver), regulates hormone levels, increases breast growth and milk duct development (along with progesterone), and decreases FSH and LH (to prevent ovulation).
    • Prolactin: increases breast milk production and mammary gland size.
    • Relaxin: decreases uterine contractions to prevent premature birth, relaxes blood vessels to increase blood flow to the placenta and kidneys, relaxes pelvic joints, and softens and lengthens the cervix during birth.
    • Oxytocin: increases at the start of labor, stimulates contractions of the uterine muscle, and increases the production of prostaglandins, which also increase contractions. It can be used to induce labor.

    Digestive System Changes

    • Nausea and vomiting: can be caused by hCG and exacerbated by low blood sugar
    • Hyperemesis gravidarum: severe morning sickness with vomiting more than 3 times a day, dehydration, and weight loss
    • Pyrosis (heartburn): gastric reflux
    • Progesterone decreases motilin (a hormone that moves food through the digestive system), leading to delayed gastric emptying
    • Growing fetus displaces stomach, increasing gastric pressure

    Urinary System Changes

    • Polyuria: frequent urination
    • Downward pressure of enlarging fetus on the bladder
    • Hypotonia: decreased muscle tone due to progesterone

    Cardiovascular System Changes

    • Increased blood volume (20-100%)
    • Increased red blood cell count (110%)
    • Increased white blood cell count (150%)
    • Varicose veins and hemorrhoids: caused by reduced venous return from the placenta
    • Uterus growth can compress vena cava in the supine position: patients should be tilted on their side
    • Decreased blood pressure
    • Increased cardiac output (increased heart rate and stroke volume)
    • Decreased vascular resistance (vasodilation)

    Respiratory System Changes

    • Diaphragm moves up 4-5 cm: decreasing functional residual capacity, which can lead to breathlessness
    • Increased skin elasticity due to increased hormone production, leading to stretch marks if the increase in size is too rapid.
    • Increased pigmentation: increased melanocyte-stimulating hormone (MSH), enhancing UV protection
    • Increased areola
    • Lineaniagra: dark line on the abdomen

    Musculoskeletal System Changes

    • Relaxin: causes ligament laxity and softening of connective tissue, particularly in the pelvic floor and ligaments of the hips
    • Changes in weight
    • Realignment of spinal curvature
    • Back pain is common

    Immune System Changes

    • Increased risk of sepsis
    • Placenta forms an immunological barrier between mother and fetus, preventing the fetus from being rejected

    Oral Cavity Changes During Pregnancy

    • Dental tissues: teeth, oral mucosa, and salivary tissues are affected.
    • Gum hypertrophy: swelling of gums
    • Increased incidence of gingivitis: inflammation of the gums
    • Increased tissue perfusion: increased blood flow, making bleeding more likely

    Comparing Root and Crown Anatomy of Primary and Permanent Teeth

    • Primary teeth: smaller than permanent teeth with a more bulbous crown, pronounced labial or buccal cingulae, higher cervical margins, more pointed cusps, softer enamel that wears down more easily and is more opaque (appears whiter), thinner enamel with consistent depth
    • Primary teeth: have larger relative pulp chambers, calcify before birth, resulting in neonatal lines, and have shorter, more delicate roots with longer roots relative to crown height in incisors and canines. Their roots are divergent and extend beyond the crown, while the pulp canals are irregular.
    • Permanent teeth: have longer and more slender roots that flare out more.
    • Neonatal lines: form in primary and permanent molars due to pressures of growth, calcifying before birth.

    Exfoliation Dates of Primary Dentition and the Subsequent Eruption Dates of the Permanent Dentition

    • Mixed dentition begins at 6 years old
    • Permanent teeth erupt in groups
    • Teeth emerge usually when 75% of their roots are completed
    • Root completion takes 2-3 years after tooth eruption
    • 6 years old: mandibular central incisor, mandibular first permanent molar, and maxillary first permanent molar erupt
    • 7 years old: maxillary central incisors and mandibular lateral incisors erupt
    • 8 years old: maxillary lateral incisors erupt
    • 9 years old: mandibular canines and first and second molars erupt
    • 10 years old: maxilla and mandibular canines and second premolars erupt
    • 11 years old: roots of all permanent incisors and first molars are expected to be complete
    • 12 years old: maxillary canine and second premolars, and mandibular second premolars erupt
    • 13-15 years old: completion of permanent teeth roots, eruption of second premolars, and development of third molars
    • 18-21 years old: eruption of third molars

    Development of Permanent Teeth (7-21 Years)

    • Follows the same pattern of calcification and root formation
    • 7 years old:
      • Maxillary central incisors (I1): crown completion.
      • Mandibular central incisors (I1): root completion.
      • Mandibular lateral incisors (I2): root completion.
      • Mandibular first molars (M1): root completion.
      • Maxillary lateral incisors (I2): crown completion.
      • Maxillary first molars (M1): root completion.
    • 9 years old:
      • Maxillary canines (C): crown completion.
      • Mandibular canines (C): crown completion.
      • Mandibular first premolars (PM1): crown completion.
      • Maxillary first premolars (PM1): crown completion.
    • 10 years old:
      • Mandibular second molars (M2): crown completion.
    • 11 years old:
      • Maxillary second premolars (PM2): crown completion.
      • Mandibular second premolars (PM2): crown completion.
    • 12 years old: 0 Maxillary canines (C): root completion.
      • Mandibular canines (C): root completion.
      • Maxillary second molars (M2): root completion.
    • 13 years old:
      • Mandibular second molars (M2): root completion.
    • 16 years old:
      • Maxillary third molars (M3): crown completion.
    • 17 years old:
      • Mandibular third molars (M3): crown completion.
    • 18-25 years old:
      • Maxillary third molars (M3): root completion.
      • Mandibular third molars (M3): root completion.

    Mixed Dentition and its Relevance to Restoration

    • Normal variations exist, such as second molars erupting before premolars in the mandibular arch, which can lead to crowding, or canines erupting before premolars in the maxillary arch, which can force canines labially out of the arch.
    • Asymmetries between sides can occur, but normally teeth should erupt within 6 months of each other. If this doesn't happen, it should be investigated further.

    Restorative Considerations

    • Carious progression is faster in primary teeth due to thinner enamel and dentine.
    • Restoration should be done as soon as possible.
    • Pulp is higher in primary teeth, making them more vulnerable to carious acids.
    • Flat contact points make them more difficult to clean.

    Preventive Considerations

    • Emphasize good oral hygiene and educate patients about the increased risk of caries on permanent teeth if there were caries during the mixed dentition.
    • Erupting teeth are difficult to clean, and tender gums can contribute to poor cleaning habits.
    • Consider stainless steel crowns (SSC) if proximal surfaces are involved.
    • Primary molars have conical anterior roots that make them easy to remove.
    • Flared molar roots require careful removal as the premolar buds are located close by.

    Problems with Premature Loss

    • In the absence of crowding, early loss has little to no effect on the permanent dentition.
    • Crowding can lead to space loss in the upper arch, greater than in the lower arch. The loss of a second primary molar leads to greater space loss than the loss of a first primary molar.
    • Extraction after the age of 10 years results in minimal space loss.
    • Early loss can cause mesial drift, leading to crowding and occlusal irregularities, as well as distal drift of anterior teeth.

    Oral Histology

    • Dental Pulp
      • Loose connective tissue containing capillaries, nerves, extracellular matrix of collagen I and II, proteoglycans, fibroblasts, odontoblasts, stem/undifferentiated mesenchymal cells, lymphocytes, plasma cells, and macrophages.
    • Periodontal Ligament (PDL)
      • Connective tissue that anchors the tooth to the alveolar bone. Contains:
        • Principal fibers: collagen types I and III.
        • Sharpey's fibers: anchoring fibers that connect the cementum and the alveolar bone.
        • Blood vessels and nerves.
        • Cells: fibroblasts, osteoblasts, osteoclasts, cementoblasts, cementoclasts, epithelial rests of Malassez, macrophages, and stem cells.

    Structure and Function of Oral Tissues

    • Stratified squamous epithelium: various types are found in the mouth
      • Buccal/labial lining: lines the cheeks and lips.
      • Masticatory surfaces: hard palate, attached gingiva, dorsum of the tongue.
      • Specialized cells: taste buds.
    • Keratinization varies depending on the location and function of the tissue.

    Neurulation

    • Neural tube: forms from the neural plate, which thickens and separates to form the floor of the amniotic cavity.
    • Forebrain, midbrain, and hindbrain: form from the anterior portion of the neural tube.
    • Rhombomeres: eight bulges that develop from the part of the neural tube associated with the hindbrain.
    • Somitomeres: contribute to development of head muscles.

    Somites

    • Each somite is composed of three parts:
      • Sclerotome: forms two adjacent vertebrae and articulating discs.
      • Myotome: gives rise to muscles.
      • Dermatome: forms the connective tissue of the skin.

    Rhombomeres

    • Rhombomeres 1 and 2, along with the midbrain, form the face and the first branchial arch.
    • Neural crest cells from rhombomeres 3 onwards contribute to the formation of pharyngeal structures.

    Neural Crest

    • A group of cells located at the dorsal margin of closing neural folds.
    • They become separate from the neuroectoderm.
    • They undergo epithelial-mesenchymal transformation, acquiring a migratory and differentiating capacity.
    • Neural crest cells exhibit stem cell and progenitor cell properties.
    • They emerge during the 3rd and 4th weeks of embryo development.

    Neural Crest Cell Differentiation

    • Signaling molecules: Wnt and FGF, secreted by surrounding non-neural ectoderm.
    • Induction: induces differentiation of neural crest cells.
    • Competence: determined by the expression of members of the "Snail zinc-finger transcription factor family," repressing the expression of the cell adhesion molecule E-cadherin.
    • Origin: most of the connective tissue of the head.
    • Embryonic connective tissue: derived from ectomesenchyme.
    • Essential for: craniofacial skeleton and tooth development.
    • Neural crest cells: contribute to all tissues of the tooth, except enamel and a portion of the cementum.

    Stages of Neural Crest Cell Development

    1. Growth: cell division and proliferation
    2. Morphogenesis: cellular rearrangement and migration
    3. Cell differentiation: specialization into various cell types
    4. Facial anomalies: can result from disruptions in neural crest cell differentiation and migration.

    Cyclops

    • Defects: result from failure of the midline structures to separate, leading to the formation of a single eye.
    • Multifactorial etiology: combination of genetic and environmental factors.
    • Disruption during week 6-7
    • Variations: median, bilateral, oblique, lateral, and median mandibular.

    Cleft Lip and Palate

    • Can occur: between the lip and palate.
    • Forms:
      • Normal: no cleft lip or palate.
      • Cleft lip + alveolus: cleft involving the lip and alveolar process.
      • Cleft palate: cleft of the palate.

    First Arch Syndromes

    • Congenital abnormalities of the craniofacial region are often associated with changes in the pharyngeal arches.
    • Neural crest cell migration into the first pharyngeal arch is deficient during week 4.
    • Possible causes: reduced proliferation or increased cell death affecting neural crest cells.
    • Syndromes: Pierre Robin sequence and Treacher Collins syndrome.

    Pierre Robin Sequence

    • Heterozygous birth defect: affects both males and females equally.
    • Prevalence: 1 in 8500 births.
    • Inheritance: autosomal recessive, with possible X-linked inheritance.
    • Characteristics: micrognathia (small lower jaw), glossoptosis (backward displacement of the tongue), ear defects, and speech defects.

    Treacher Collins Syndrome

    • Prevalence: 1 in 10,000 births
    • Inheritance: autosomal dominant
    • Characteristics: negative canthal tilt, micrognathia, absent or malformed ears, cleft lip and palate.
    • Genetic basis: mutation in the TCOF1 gene, disrupting the synthesis of the treacle protein, which is crucial for neural crest cell development and migration.

    Environmental Factors for Congenital Defects

    • Infections:
      • Rubella virus: can cause congenital rubella syndrome.
      • Treponema pallidum: causative agent of syphilis.
    • X-rays: radiation can damage developing cells.
    • Cortisone: can affect fetal development.
    • Hormones: certain hormonal imbalances can lead to defects.
    • Nutritional deficiencies: lack of essential nutrients can disrupt embryologic development.
    • Alcohol abuse: fetal exposure to alcohol can lead to fetal alcohol spectrum disorder.

    Fetal Alcohol Spectrum Disorder (FASD)

    • Caused by: drinking more than 4 units of alcohol per day during pregnancy.
    • 33% of children with FASD have mothers who are alcoholics.
    • Severity: dependent on the time frame and amount of alcohol exposure during the pregnancy.

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