Med Gen Week1

Fall 2026

Monogenic (Mendelian) Diseases

Diseases caused by mutations in a single gene that lead to specific hereditary conditions. Examples include cystic fibrosis (autosomal recessive) and sickle cell anemia (autosomal recessive).

Multifactorial Diseases

Diseases caused by the combination of multiple genes, environmental factors, and lifestyle. Examples include diabetes and asthma.

Pharmacogenetic

The study of how your unique genes affect the way your body responds to medications.

Developmental Milestones Guidelines

CDC: Informal surveillance and parent-provider discussion; 2 mo to 5 years
Denver II: Standardized screening test; Birth to 6 years

Eugenics

Pseudoscience that claims complex human traits can be improved by selective breeding

Sources of Genetic Variation

Amount of DNA: Chromosomal (CNVs)

Genetic sequence itself: SNVs; repeat expansion disorders

Epigenetic methylation: Methylation conditions; UPD

Acrocentric chromosome

The centromere is located very close to one end, creating one long arm (q-arm) and one extremely short arm.

Chromosomes 13, 14, 15, 21, 22, and the Y chromosome are acrocentric.

Chromatin

Loose, uncoiled, combination of DNA wrapped around structural histone proteins. DNA is accessible and active for protein synthesis.

Chromossome

A tightly condensed, organized package of DNA and proteins. Visible during cell division (mitosis or meiosis).

Chromatid

One of two identical halves of a chromosome that has been replicated

Gain of Function Variant

Variants that increase the amount of the normal protein OR increase the normal function OR create a new function of a protein

Loss of Function Variant

Variants that result in decreased/absent amount of normal protein. Examples are: most autosomal recessive conditions, monosomies, and microdeletions.

Note: most common variant type

Dominant Negative Variant

Genetic variant that produces a faulty protein which actively blocks and disrupts the normal protein made by the healthy gene copy

Locus

Location of a gene on a chromosome

Allele

Alternate forms of the same gene/One of multiple versions of a gene.

Genotype

Refers to the specific information encoded at a given locus in the genome (the actual DNA sequence at a specific locus)

Key types:
Homozygous Dominant, Homozygous Recessive, Heterozygous

Phenotype

Set of observable characteristics or traits of an organism. Examples are height, eye color, behavior, and biochemical properties.

Locus Heterogeneity

Phenomenon where many genotypes (different genes) cause a specific/same phenotype.

Allelic Heterogeneity

Phenomenon where numerous variants in one gene cause the same phenotype. Example: Cystic Fibrosis, which is caused by 1000+ variants in CFTR.

Variable Expressivity

Phenomenon where the same genotype can cause different symptoms within a phenotype from one person to the next

Gene

Section of DNA that encodes for a functional product

Incomplete Penetrance

Phenomenon where symptoms may not always occur in a person with a pathogenic genetic variant

Pleiotropy

Phenomenon where a genetic variant causes numerous symptoms in unrelated body systems in an affected person