embryo

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Questions and Answers

What is the primary role of tertiary dentin production in response to tooth injury?

To protect the pulp from further damage (correct)

To enhance enamel formation and protection

To replace lost enamel with new dentin

To increase the functional capacity of odontoblasts

What is the primary consequence of reduced odontoblast activity as teeth age?

Higher rates of enamel mineralization

Increased production of tertiary dentin

Slower production of secondary dentin (correct)

Enhanced tooth regeneration capabilities

What triggers the differentiation of inner enamel epithelial cells into ameloblasts?

Increased mineral content in the enamel matrix

Signals from the underlying odontoblasts (correct)

Presence of external environmental factors

Interactions with dental pulp cells

During the secretory phase of amelogenesis, which proteins are primarily produced and secreted by ameloblasts?

Amelogenin, ameloblastin, and enamelin Signup and view all the answers

What happens to ameloblasts once the full thickness of enamel is reached?

They undergo apoptosis and disappear Signup and view all the answers

What is the primary event occurring during the first week of human development after fertilization?

Conversion of the morula into a blastocyst Signup and view all the answers

Which of the following layers is NOT formed from the epiblast during the process of gastrulation?

Trophoblast Signup and view all the answers

What is the consequence of hypermethylation of gene promoter regions?

Decreased gene transcription Signup and view all the answers

Which embryonic layer is primarily responsible for forming the liver and pancreas?

Endoderm Signup and view all the answers

Which condition results from a malfunction of meiosis leading to an abnormal number of chromosomes?

Turner syndrome Signup and view all the answers

What role do homeobox genes play during development?

Regulate cell differentiation and patterning Signup and view all the answers

What is a characteristic feature of Turner syndrome?

Partial or complete missing X chromosome Signup and view all the answers

Which of the following is an example of a single gene malfunction disorder?

Osteogenesis imperfecta Signup and view all the answers

What is the origin of ameloblasts in tooth development?

Ectodermal origin from oral cavity lining Signup and view all the answers

Which cell type is derived from the dental papilla?

Odontoblasts Signup and view all the answers

Which of the following signaling molecules is essential for promoting odontoblast differentiation?

BMPs Signup and view all the answers

What role does Shh play in tooth development?

Marks the future site of tooth development Signup and view all the answers

What is the primary origin of dental pulp?

Mesoderm from neural crest cells Signup and view all the answers

Which structure is primarily responsible for the development of cementoblasts?

Dental follicle Signup and view all the answers

The morphology of teeth is largely determined by which process?

Morphogenesis Signup and view all the answers

What is the function of FGFs in tooth development?

Regulate proliferation and survival in epithelium and mesenchyme Signup and view all the answers

What is the definitive role of epithelial-mesenchymal interactions in odontogenesis?

Coordinating the deposition of enamel and dentin Signup and view all the answers

What consequence can arise from disruption in Shh signaling during tooth development?

Supernumerary or missing teeth Signup and view all the answers

What is the first step in nervous system development?

Thickening of ectoderm at the rostral end Signup and view all the answers

Which structures are derived from somites?

Muscles, vertebrae, and skin connective tissue Signup and view all the answers

What does the neural crest become during development?

Most connective tissue of the head Signup and view all the answers

Which molecules are primarily involved in inducing neural crest cell formation?

Morphogens like Wnt and FGF Signup and view all the answers

The rhombomeres are associated with which part of the developing nervous system?

Hindbrain segment and craniofacial development Signup and view all the answers

What distinguishes the three parts of a somite?

Sclerotome, myotome, and dermatome Signup and view all the answers

What role do somitomeres play in development?

Contribute to head muscle formation Signup and view all the answers

What is an important function of E-cadherin in neural crest development?

Facilitates cell adhesion Signup and view all the answers

Which structures are primarily derived from the fore- and midbrain regions of the neural tube?

Forebrain, midbrain, and hindbrain Signup and view all the answers

What defines the competence of neural crest cells during development?

The expression of Snail transcription factors Signup and view all the answers

What is the significance of the interaction between neural crest mesenchyme and sensory facial ectodermal placodes during facial development?

It is crucial for epithelial-mesenchymal interactions. Signup and view all the answers

At which stage of gestation does the formation of the secondary plate, distinguishing the oral and nasal cavities, occur?

Week 7 to 8 Signup and view all the answers

Which anatomical structure primarily influences tongue development by providing space for its forward movement?

The head position Signup and view all the answers

How does the maxilla develop in relation to the zygomatic region?

Ossification spreads towards the zygomatic process. Signup and view all the answers

What occurs in the formation of the condylar cartilage during mandibular development?

It appears as a thin mass at 20 weeks. Signup and view all the answers

What is a major clinical consideration associated with holoprosencephaly?

It is caused predominantly by chromosomal abnormalities. Signup and view all the answers

Which structure is responsible for forming the articular disk in the temporomandibular joint?

The mesenchyme adjacent to the developing ramus Signup and view all the answers

During what gestational week does intramembranous ossification begin in the formation of the tongue?

Week 7 Signup and view all the answers

What developmental process is indicated by the formation of nasolacrimal ducts?

The sinking of ectodermal cells below the surface. Signup and view all the answers

Which of the following occurs after the degeneration of Meckel's cartilage?

The development of the ramus. Signup and view all the answers

Which cell type directly contributes to the production of collagen fibers in the periodontal ligament?

Fibroblasts Signup and view all the answers

What role does cementum play in tooth stability?

Anchors the tooth by providing attachment points for the periodontal ligament Signup and view all the answers

How does the alveolar bone formation relate to dental development?

It forms in response to signals from the dental follicle and periodontal ligament Signup and view all the answers

In what manner does the periodontal ligament allow tooth movement?

By providing a shock-absorbing function while allowing slight movement Signup and view all the answers

What tissue does the gingiva primarily develop from?

Oral mucosa Signup and view all the answers

What is formed during the transition from a bilaminar disc to a trilaminar embryo disc?

Change in cell adhesive properties and movement Signup and view all the answers

Which embryonic layer is responsible for forming components of the circulatory system?

Mesoderm Signup and view all the answers

What characterizes the primary chromosomes affected in Turner syndrome?

Absence of one X chromosome Signup and view all the answers

How does DNA methylation typically affect gene transcription?

Decreases transcription by adding methyl groups to cytosines Signup and view all the answers

What is one role of non-coding RNA in embryonic development?

Regulate expression of genes and chromosomes Signup and view all the answers

What type of chromosomal abnormality is primarily associated with Trisomy 21?

Trisomy of the 21st chromosome leading to 47 chromosomes Signup and view all the answers

What is one major impact of metabolic abnormalities in Turner syndrome?

Increased likelihood of congenital heart defects Signup and view all the answers

Which layer primarily forms the epithelial lining of the digestive tract?

Endoderm Signup and view all the answers

What process do odontoblasts engage in to protect the pulp from damage in response to decay or injury?

Tertiary dentin production Signup and view all the answers

What happens to odontoblasts as the tooth ages?

Their activity decreases and they may undergo apoptosis. Signup and view all the answers

What is the role of signals from odontoblasts in enamel formation?

Induce differentiation of inner enamel epithelial cells into ameloblasts. Signup and view all the answers

During the secretory phase of amelogenesis, what is produced by ameloblasts?

Enamel matrix proteins Signup and view all the answers

What morphological change occurs in ameloblasts during differentiation?

They elongate and their nuclei move towards the base. Signup and view all the answers

What is the fate of ameloblasts once the full thickness of enamel is achieved?

They undergo apoptosis and lose Tomes' process. Signup and view all the answers

What is one characteristic feature of the enamel prisms formed during mineralization?

They are organized by Tomes' process. Signup and view all the answers

How do odontoblast-like cells contribute to tooth development?

They produce reparative dentin after odontoblast apoptosis. Signup and view all the answers

Which of the following is NOT involved in the phase of enamel matrix production?

Collagen Signup and view all the answers

What cellular change assists ameloblasts in increasing surface area for enamel secretion?

Retreating to a pyramid shape as they secrete. Signup and view all the answers

Which of the following structures is formed from the neural tube during early nervous system development?

Rhombomeres Signup and view all the answers

What are the three parts of a somite and their fates?

Sclerotome, myotome, and dermatome; form vertebrae, muscles, and skin connective tissue. Signup and view all the answers

Which factor is critical for the migration and differentiation of neural crest cells?

Signaling molecules like Wnt and FGF from surrounding ectoderm Signup and view all the answers

What distinguishes the embryonic origin of connective tissue of the head from other body regions?

It forms primarily from neural crest cells. Signup and view all the answers

Which neural crest-derived structures are crucial for craniofacial development?

Cartilage and bone of the craniofacial skeleton. Signup and view all the answers

What are rhombomeres and their significance during development?

They are divisions in the hindbrain that contribute to craniofacial structure formation. Signup and view all the answers

In the context of somite development, what does the term 'Ceff diff' likely refer to?

Cellular differentiation processes that contribute to muscle and vertebral formation. Signup and view all the answers

What is the role of the Snail zinc-finger transcription factor family in neural crest cells?

Repressing the expression of E-cadherin to facilitate epithelial-mesenchymal transition. Signup and view all the answers

What occurs during the transformation of the neural plate into the neural tube?

The neural folds raise and create a groove that eventually fuses. Signup and view all the answers

What is the fate of the sclerotome in somite development?

It differentiates into vertebrae and articulating discs. Signup and view all the answers

What is the role of odontoblasts in the process of dentinogenesis?

They secrete predentin Signup and view all the answers

What is the effect of repeated trauma on tertiary dentin?

It forms a bonelike and atubular structure Signup and view all the answers

What triggers the differentiation of pre-odontoblasts into mature odontoblasts?

Induction from the inner enamel epithelium Signup and view all the answers

What is the primary factor influencing the deposition of secondary dentine?

Apoptosis of odontoblasts Signup and view all the answers

What type of collagen is primarily found in the organic matrix secreted by odontoblasts?

Type I collagen Signup and view all the answers

What is the first layer of dentin formed during dentinogenesis called?

Mantle dentin Signup and view all the answers

How do odontoblasts respond to stimuli encountered during their lifetime?

By producing secondary dentin Signup and view all the answers

What structural feature in dentin forms as a result of the cytoplasmic processes of odontoblasts?

Dentin tubules Signup and view all the answers

What happens to odontoblasts as teeth age?

They contribute to the formation of tertiary dentin Signup and view all the answers

What is the distinct orientation feature of polarized odontoblasts?

Nucleus at one end and processes at the opposite end Signup and view all the answers

Study Notes

Human Development Weeks 1-3

Week 1: Fertilized egg undergoes rapid divisions, forming a ball of cells called a morula. Fluid accumulates within the morula, leading to cell rearrangement and the formation of a blastocyst (blastula).
Week 2: On day 8, cells of the embryoblast differentiate into a two-layered disc, known as the bilaminar disc. The ectodermal layer (dorsal) is columnar and reorganizes to form the amniotic cavity. The secondary yolk sac (ventral), also known as the endothermal layer, forms the roof of a second cavity.
Week 3: The bilaminar embryo disc transitions into a trilaminar embryo disc with the formation of the primitive streak. Cell shape changes, rearrangement, movement, and alterations in adhesive properties are key events in this process.
Gastrulation: The process of transforming the blastula into a gastrula involves the enlargement of ectodermal and endodermal cells. Following two weeks, the axis of the embryo is established with a cranial/prochordal end (head end or rostral) and a caudal/cecal plate (tail end).
Cell Migration: Cells migrate through the primitive streak, changing shape and diverting laterally and cephalically. Cells from the epiblast break off, travel through the primitive pit, and interact with the epiblast layer, forming the three germ layers: endoderm, mesoderm, and ectoderm.
- Endoderm: Formed by epiblast cells migrating from the primitive pit, displacing the hypoblast.
- Mesoderm: Located between the endoderm and ectoderm; comprises intra- and extraembryonic mesoderm.
- Ectoderm: Consists of remaining epiblast cells at the primitive pit.
Germ Layer Fate: These three germ layers are responsible for forming different fetal tissues.
- Ectoderm: Forms the epidermis of the skin, cornea and lens of the eye, and the nervous system.
- Mesoderm: Forms the notochord, musculoskeletal system (MSK), muscle layer of the stomach and intestines, circulatory system, respiratory system, and outer lining of the gut.
- Endoderm: Forms the liver, pancreas, lining of the urethra, bladder, and reproductive system, and the epithelial lining of the digestive and respiratory tracts.

Embryological Defects

Down's Syndrome (Trisomy 21): Occurs when a 24 chromosome gamete fuses with a normal gamete, resulting in a zygote with 47 chromosomes. The 21st chromosome pair has three chromosomes (trisomic). Characteristics include facial clefts, shortened palate, protruding and fissured tongue, and delayed eruption of teeth.
Turner Syndrome: The most common chromosomal disorder in females, involving the partial or complete absence of an X chromosome (monosomy). Features include dysmorphic stigmata, short stature, sexual infantilism, and renal, cardiac, skeletal, endocrine, and metabolic abnormalities.

Epigenetic Processes

DNA Methylation: Involves the addition of a methyl group to cytosines via covalent modification. Methylation in CpG regions, often located in promoter regions of target genes, can decrease gene transcription (hypermethylation) or increase gene transcription (hypomethylation).
Histone Modification: Positively charged nuclear proteins (histones) around which DNA wraps can be modified, affecting the activity of promoters and thus gene expression.
Non-Coding RNA: A cluster of RNA that doesn't encode functional proteins can regulate gene and chromosome expression, playing a significant role in cell differentiation.
Genetics and Epigenetics: Genetics determines inherited traits and disorders, while epigenetics dictates which genes are activated. This regulation is achieved by chemical modifications of DNA and proteins, determining when and where genes are active.

Neural Crest Formation and Fate

Neural Tube Development: The nervous system originates when the ectoderm thickens at the rostral (head) end, forming the neural plate. The margins of the plate elevate, creating neural folds that enclose a groove. These folds eventually merge to form the neural tube. The thickening and separation of the neural tube forms the floor of the amniotic cavity.
Brain Development: The anterior portion of the neural tube expands, forming the forebrain, midbrain, and hindbrain. The hindbrain develops eight bulges called rhombomeres. Somites contribute to head muscles.

Somites

Each somite differentiates into three parts:
- Sclerotome: Develops into two adjacent vertebrae and articulating discs.
- Myotome: Originates from muscles.
- Dermatome: Forms connective tissue of the skin.

Rhombomeres

The midbrain and rhombomeres 1 and 2 contribute to the face and the first branchial arch.
Neural crest cells from rhombomeres 3 onward contribute to pharyngeal structures.

Neural Crest

Origin: Cells at the dorsal margin of closing neural folds become distinct from the neuroectoderm.
Transformation: Neural crest cells undergo epithelial-mesenchymal transformation after receiving inductive signals.
Stem Cell Potential: Exhibit exceptional stem and progenitor cell capabilities.
Timing: Develops during the third and fourth weeks of embryonic development.

Neural Crest Cells

Signaling Molecules: Wnt and FGF, secreted by surrounding nonneural ectoderm, induce the neural crest cell cascade.
Competence: Expression of members of the "Snail zinc-finger transcription factor family" represses the expression of the cell adhesion molecule E-cadherin, making cells competent to migrate and form the neural crest.
Fate: Neural crest cells are responsible for the majority of connective tissue in the head, including tissues of the teeth (except enamel and some cementum).

Branchial Arch Formation and Development

Formation: Develop as a series of bulges in the lateral pharyngeal walls of the embryo.
Neural Crest Contribution: Contribute to skeletal, muscular, and connective tissues of the head and neck regions.
Fate: Each arch develops a specific characteristic:
- Arch 1: (mandibular arch) Forms the mandible, muscles of mastication, and the Meckel's cartilage.
- Arch 2: (hyoid arch) Develops into the stapes, styloid process, hyoid bone, facial muscles, and the second branchial arch.
- Arch 3: Forms the greater cornu of the hyoid bone, stylopharyngeal muscle, and contributing structures to the pharynx.
- Arch 4: Forms parts of the larynx and muscles of the pharynx.
- Arch 6: Contributes to the larynx muscles and muscles of the soft palate.

Facial Development

Interaction: Interactions between neural crest mesenchyme and sensory facial ectodermal placodes drive facial development.
Epithelial-Mesenchymal Interactions: These interactions involve sequential activation of specific genes and signaling molecules.
Week 4: The frontonasal process starts to form.
Week 5: The maxillary and mandibular processes appear.
Week 6:
- The two mandibular processes fuse to form the lower jaw.
- The maxillary processes grow below the lateral nasal processes towards the medial nasal processes.
- The nasolacrimal groove forms, with an ectodermal rod of cells sinking below the surface to later canalize into the nasolacrimal duct.

Tongue Development

Secondary Plate: The formation of the secondary plate distinguishes between the oral and nasal cavities during weeks 7 and 8, completing by the third month.
Head Position: The head's position is crucial for tongue development. At 9 weeks, the head lifts to provide space for tongue movement.
Origin: Starts developing at four weeks of gestation.
Formation: The anterior two-thirds of the tongue form from
- Lingual swellings
- Tuberculum impar (derived from the first arch).
Hypobranchial Eminence: The hypobranchial eminence overgrows the second arch.
Pharyngeal Arches: The pharyngeal arches meet at the midline below the primitive mouth.
Nerve Development: Develops alongside the nerve of the first arch.

Mandible Development

Intramembranous Ossification: Begins at seven weeks, forming bone from existing cartilage. The bone formation spreads rapidly, forming the tooth germs.
Ramus Development: Spreads posteriorly into the mesenchyme of the first arch, turning away from Meckel's cartilage. This divergence, marked by the lingula, completes by week 10.
Meckel's Cartilage: Degenerates to make space for new bone.
Secondary Cartilages: Further growth occurs from three secondary cartilages: condylar (most important), coronoid, and symphyseal cartilage.
Condylar Cartilage: Forms at 12 weeks, persists until late 20s.

Maxilla Development

Ossification Center: Begins alongside the nasal capsule cartilage, appearing at the angle between the anterosuperior dental nerve and the inferior orbital nerve.
Spread: Ossification expands posteriorly towards the developing zygoma, anteriorly towards the incisor region, and superiorly to form the frontal process.
Zygomatic/Malar Cartilage: Appears in the developing zygomatic process, playing a major role in zygomatic development.
Maxillary Sinus: Develops at 16 weeks, forming a shallow groove on the nasal aspect.

TMJ Development

Formation: Initially formed from membranous centers of ossification.
Mesenchyme: A broad band of undifferentiated mesenchyme between the developing ramus of the mandible and the squamous tympanic bone forms a dense strip of mesenchyme as the condylar cartilage develops.
Joint Cavity: Adjacent mesenchyme forms the joint cavity.
Articular Disc: The strip develops into the articular disc.

Clinical Considerations and Anomalies in Facial Development

Holoprosencephaly: The forebrain fails to divide into two separate hemispheres and ventricles, occurring in 1:10,000 births. The cause is unclear, but potential factors include chromosomal abnormalities, gene mutations, maternal diabetes, infection, and drugs.

Tooth Development

Epithelial-Mesenchymal Interactions: These interactions are crucial in tooth development, involving numerous growth factors, signaling molecules, and transcription factors. The mesenchyme, derived from neural crest cells, gives rise to the dental papilla and follicle. The epithelial cells, originating from ectoderm, form the enamel.
Tooth Development Stages: The process involves several stages:
- Bud Stage: Initial stage with a condensation of mesenchymal cells forming the dental mesenchyme. The dental lamina (a thickening of the oral epithelium) forms.
- Cap Stage: The tooth bud becomes invaginated, and the dental papilla and follicle develop. The ameloblasts differentiate and begin to secrete enamel matrix.
- Bell Stage: The enamel organ is fully formed, and the dentin formation begins.
Key Signaling Molecules:
- FGFs: Regulate cell proliferation, survival, and differentiation in the epithelium and mesenchyme.
- BMPs: Promote odontoblast differentiation.
- Shh: Involved in tooth patterning, shaping the tooth germ, and influencing tooth eruption.
Importance of Epithelial-Mesenchymal Interactions:
- Determine the shape and size of the tooth.
- Control the differentiation of cells into ameloblasts, odontoblasts, and cementoblasts.
- Coordinate the deposition of enamel, dentin, and cementum.
Role of Shh:
- Marks future sites of tooth development in the dental placode.
- Triggers the condensation of neural crest-derived mesenchymal cells, forming dental mesenchyme.
- Regulates the formation of the dental lamina.
- Expressed at high levels by epithelial cells during the bud stage, promoting growth and invagination of the tooth bud.
- Shapes the tooth germ in the cap stage and controls the proliferation of epithelial cells in the enamel organ, defining regions of the developing tooth (enamel organ, dental papilla, and dental follicle).
- Plays a crucial role in morphogenesis (shape determination) and cusps formation.
- Disruptions in Shh can result in supernumerary teeth, missing teeth, or abnormal tooth shapes.
- Contributes to the development of Hertwig's epithelial root sheath (HERS), which encloses the tooth root.
Morphogenesis: Involves cell proliferation and movement to shape the tooth.
Histogenesis: The differentiation of cells into fully formed dental tissues.
Tooth Type: Determined by the patterning of the dentition, controlled by the spatially restricted expression of homeobox genes, like the SEK gene.

Amelogenesis (Enamel Formation)

Simultaneous Process: Occurs concurrently with odontogenesis (dentin formation), starting at the enamel-dentine junction.
Ameloblast Formation:
- Origin: Ameloblasts are derived from the inner enamel epithelium of the enamel organ, part of the developing tooth germ.
- Induction: Signaling from the underlying odontoblasts induces the inner enamel epithelial cells to differentiate into ameloblasts. This interaction is crucial for enamel formation initiation.
Morphological Change:
- Polarization: Differentiated ameloblasts elongate and become polarized, with the nucleus migrating towards the base of the cell and the enamel secretion region (Tomes' process) at the top.
Secretory Phase (Enamel Production):
- Enamel Matrix Production: Ameloblasts in the secretory stage produce and secrete proteins forming the enamel matrix, primarily amelogenin, ameloblastin, and enamelin.
- Tomes' Process: Helps to organize the enamel crystals into the structured enamel prisms, providing enamel's strength and hardness.
- Mineralization: The enamel matrix begins to mineralize, continuing as the enamel matures. Ameloblasts deposit calcium and phosphate into the enamel matrix.
Ameloblast Retraction: Ameloblasts become pyramid-shaped as they retreat, with their nuclei shifting lower, increasing surface area.
Cell Death: About 50% of ameloblasts die during this stage.
Tomes' Process Loss: Ameloblasts lose their Tomes' process after achieving full enamel thickness.

Tertiary (Reparative) Dentin

Production: In response to injury or decay, odontoblasts produce tertiary (reparative) dentin to protect the pulp from damage.

Aging and Degeneration

Reduced Activity: Odontoblast activity declines with age, slowing down the production of secondary dentin. Odontoblasts shrink or lose functionality over time.
Cell Death: Odontoblasts may eventually undergo apoptosis (programmed cell death) due to aging or substantial injury. Damaged odontoblasts can be replaced by new cells called odontoblast-like cells derived from the dental pulp to continue producing reparative dentin.

Human Development Weeks 1-3: Gametogenesis to Trilaminar Embryo

Week 1:
- Fertilized egg undergoes rapid divisions, forming a ball of cells called a morula.
- Fluid accumulates in the morula, causing cell realignment and forming a blastocyst.
Week 2:
- On day 8, the embryoblast (inner cell mass) differentiates into two layers: the ectoderm (dorsal) and endoderm (ventral).
- The ectodermal layer reorganizes to create the amniotic cavity.
- The endodermal layer forms the roof of the secondary yolk sac.
Week 3:
- The bilaminar embryo disc transitions into the trilaminar embryo disc.
- Gastrulation initiates with the formation of the primitive streak.
- Cell shapes, arrangement, and movement change as cells migrate.

Gastrulation

Cell Migration: Cells migrate through the primitive streak, altering shapes and moving laterally and cephalically.
Three Germ Layers Formation:
- Endoderm: Cells from the primitive pit displace the hypoblast, forming the endoderm.
- Mesoderm: Cells lie between the endoderm and ectoderm, forming the mesoderm.
- Ectoderm: Remaining epiblast cells at the primitive pit form the ectoderm.
Tissue Differentiation:
- Ectoderm: Forms epidermis of skin, cornea and lens of the eye, nervous system.
- Mesoderm: Forms notochord, musculoskeletal system, muscle layers of the stomach and intestines, circulatory and respiratory systems, and the outer lining of the gut.
- Endoderm: Forms liver, pancreas, lining of urethra, bladder, reproductive system, and epithelial lining of the digestive and respiratory tracts.

Embryological Development Defects

Defects can arise from meiosis malfunction, leading to abnormal numbers of chromosomes.
Down Syndrome (Trisomy 21):
- Caused by an extra chromosome on the 21st pair.
- Characterized by facial clefts, shortened palate, protruding tongue, fissured tongue, and delayed tooth eruption.
Turner Syndrome:
- Most common chromosomal disorder in females.
- Results from a partial or complete absence of an X chromosome.
- Characterized by dysmorphic stigmata (abnormal physical features), short stature, sexual infantilism, and renal, cardiac, skeletal, endocrine, and metabolic abnormalities.
Single Gene Malfunctions:
- Autosomal dominant: Achondroplasia, cleidocranial dysostosis, osteogenesis imperfecta, and dentinogenesis imperfecta.
- Autosomal recessive: Chondroecto dysplasia, cystic fibrosis.

Epigenetic Processes in Development

DNA Methylation:
- The addition of a methyl group to cytosines, influencing gene expression.
- Hypermethylation decreases gene transcription.
- Hypomethylation increases gene transcription.
Histone Modification:
- Modifications to positively charged nuclear proteins (histones) that DNA wraps around, affecting gene expression.
Non-coding RNA:
- RNA that does not code for proteins but regulates gene expression and chromosome structure.
Genetics and Epigenetics:
- Genetics determines the inherited traits and disorders.
- Epigenetics controls gene activation through chemical modifications to DNA and proteins, influencing when and where genes are active.