Genetic Diseases - Basis for Genetic Disease and Inheritance

Vocabulary flashcards covering genetic mutations, allele concepts, inheritance patterns (autosomal dominant/recessive, X-linked), chromosome disorders, Down syndrome, and prenatal diagnostics.

Mutation

The permanent change in the sequence of nucleotides (C, T, A, or G) that underlies genetic diseases.

Base pair substitution

A mutation in which one nucleotide pair is replaced by another.

Frameshift mutation

A mutation caused by insertion or deletion of a nucleotide pair, shifting the reading frame.

Insertion

A mutation where one or more nucleotides are added into the DNA sequence.

Deletion

A mutation where one or more nucleotides are removed from the DNA sequence.

Allele

Different DNA sequences (versions) of the same gene.

Locus

The specific site on a chromosome where an allele is located.

Homozygote

An individual with matching alleles at the same locus on both chromosomes.

Heterozygote

An individual with different alleles at the same locus on paired chromosomes.

Dominant allele

An allele that is expressed when present in one or two copies; uppercase convention denotes dominance.

Recessive allele

An allele that is expressed only when present in two copies; lowercase convention denotes recessiveness.

Nomenclature (A/a)

Uppercase represents the dominant allele; lowercase represents the recessive allele.

Autosomal dominant inheritance

Inheritance where one copy of a mutated allele can cause disease; about half of offspring affected; no skipped generations (example: Achondroplasia).

Achondroplasia

An autosomal dominant disorder affecting skeletal development.

Marfan syndrome

An autosomal dominant disorder caused by a mutation in the collagen gene affecting connective tissue.

Huntington’s disease

An autosomal dominant, trinucleotide repeat (CAG) disorder causing adult-onset brain degeneration.

Autosomal recessive inheritance

Inheritance requiring two mutated copies; about 25% of offspring affected when both parents are carriers; skipped generations possible.

Cystic fibrosis

Autosomal recessive disease due to a chloride channel mutation leading to thick mucus in multiple organs.

Sickle cell anemia

Autosomal recessive disease from a point mutation in hemoglobin causing sickled red blood cells under certain conditions.

X-linked recessive inheritance

Males are more often affected; females usually carriers; fathers do not pass the disease to sons; skipped generations can occur in females.

Hemophilia A

X-linked recessive bleeding disorder caused by Factor VIII deficiency.

Duchenne muscular dystrophy

X-linked recessive disorder due to dystrophin mutation causing progressive muscle weakness.

Chromosome disorder

Abnormal number or structure of chromosomes; includes conditions like Down syndrome.

Karyotype

A full set of an individual's chromosomes used for diagnostic purposes.

Down syndrome (Trisomy 21)

A chromosome disorder caused by an extra copy of chromosome 21 due to nondisjunction; associated with maternal age effect.

Nondisjunction

Error in meiosis that leads to aneuploidy, such as trisomy or monosomy.

Aneuploidy

Abnormal number of chromosomes (e.g., monosomies or trisomies) with variable viability.

Monosomy

Having a single copy of a chromosome; autosomal monosomies are usually lethal.

Trisomy

Having three copies of a chromosome; some trisomies are viable (e.g., Trisomy 21) while others are not.

Turner syndrome

Sex chromosome aneuploidy: 45,X; typically a monosomy of the X chromosome.

Klinefelter syndrome

Sex chromosome aneuploidy: 47,XXY; male with an extra X chromosome.

XXX syndrome

Sex chromosome aneuploidy: 47,XXX; females with an extra X chromosome.

XYY syndrome

Sex chromosome aneuploidy: 47,XYY; males with an extra Y chromosome.

Prenatal diagnosis

Tests to diagnose chromosome disorders before birth (e.g., amniocentesis at ~16 weeks, chorionic villus sampling at ~9–10 weeks; Quad Screen).

Amniocentesis

Prenatal diagnostic procedure sampling amniotic fluid around 16 weeks.

Chorionic villus sampling

Prenatal diagnostic procedure sampling placental tissue around 9–10 weeks.

Down syndrome features

Developmental delays, distinct facial features, congenital heart defects, increased leukemia risk, premature aging.