GENETICS

Genetics Overview

Basic Concepts

• Genes: Hereditary units passed from one generation to the next.

• Chromosomes: Found on chromosomes located in the nucleus of the cell; humans have 46 chromosomes.

  • Female: XX from mother

  • Male: XY from father

  • DNA: Contains genetic information.

Chromosome Structure

• Autosomes: Non-sex chromosomes; identical in males and females.

• Sex Chromosomes: Determine sex; XX (female), XY (male).

DNA Functionality

• Has the ability to duplicate itself, creating exact copies through cell division.

Cell Division Processes

Mitosis

• A normal form of cellular division to create identical cells.

• Stages of Mitosis:

  1. Prophase: Chromosomes condense and line up.

  2. Metaphase: Chromosomes align in the center.

  3. Anaphase: Chromatids separate.

  4. Telophase: Two nuclei form and the cell divides.

Meiosis

• A special type of cell division for germ cells.

• First Meiosis: Chromosomes line up and can exchange segments (crossing-over).

• Second Meiosis: Each chromosome splits, resulting in 23 chromosomes for each cell, essential for embryo development.

Chromosome Abnormalities

Types of Chromosomal Abnormalities

1. Molecular (mutations at the DNA level)

2. Gross (alterations in chromosome number or structure)

Euploid and Aneuploid Conditions

• Euploid: Normal number of chromosomes (46 in humans).

• Aneuploid: Abnormal number of chromosomes, e.g., Trisomy (extra chromosome).

Clinical Syndromes from Gross Abnormalities

• Trisomy 21 (Down Syndrome): Characterized by physical and intellectual disabilities.

• Trisomy 13: Severe abnormalities, often leading to infant mortality.

• Turner Syndrome: Female with a single X chromosome, causing various physical traits.

• Klinefelter Syndrome: Males with an extra X chromosome, leading to distinct characteristics such as taller stature and potential breast development.

• Cri du Chat Syndrome: Characterized by a high-pitched cry in infants due to a deletion on chromosome 5, leading to severe developmental issues.

• Wolf-Hirschhorn Syndrome: Resulting from a loss of genetic material on chromosome 4; it includes severe developmental delays and physical abnormalities.

Patterns of Inheritance

• Autosomal Dominant: Affected individuals have a 50% chance of passing the gene to offspring.

• Autosomal Recessive: Both parents must carry the gene; each child has a 25% chance of being affected.

• X-linked Dominant/Recessive: Traits linked to the X chromosome with different patterns of inheritance for males and females.

Molecular Chromosomal Abnormalities Affecting Oral Health

• Cyclic Neutropenia: Affects neutrophil counts, leading to severe dental issues.

• Papillon-Lefevre Syndrome: Causes severe periodontal disease and loss of teeth in children due to genetic factors.

• Gingival Fibromatosis: Characterized by excessive gum growth, leading to dental complications.

Inherited Disorders Affecting the Jaw and Oral Structures

• Cherubism: Causes bilateral facial swelling and dental anomalies in children.

• Ellis-Van Creveld Syndrome: Results in skeletal and dental abnormalities; fusion of gums to lips.

• Cleidocranial Dysplasia: Leads to multiple dental and skeletal abnormalities including under-developed clavicles.

• Gardner Syndrome: Characterized by osteomas in bones and tooth abnormalities.

• Nevoid Basal Cell Carcinoma Syndrome: Development of skin cancers and jaw cysts.