Genetic Diseases: Quick Reference

Vocabulary flashcards covering key terms and concepts from the lecture notes on genetic mutations, gene sequences, inheritance patterns, chromosome disorders, and Down syndrome.

Mutations

Permanent changes in the DNA sequence of nucleotides (A, C, G, T) that underlie genetic diseases.

Nucleotides

The building blocks of DNA; the bases are cytosine (C), thymine (T), adenine (A), and guanine (G).

Base pair substitution

A mutation where one base pair is replaced by a different base pair.

Frameshift mutation

Mutation caused by insertion or deletion of bases that shifts the reading frame of codons.

Alleles

Different DNA sequences (versions) of the same gene.

Locus

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

Homozygote

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

Heterozygote

An individual with two different alleles at the same locus.

Dominant allele

An allele that is expressed when present in at least one copy (in heterozygotes).

Recessive allele

An allele that is expressed only when present in two copies (homozygotes).

Nomenclature of alleles (A vs a)

Uppercase letters denote dominant alleles and lowercase letters denote recessive alleles, regardless of disease.

Autosomes

Chromosome pairs that are not sex chromosomes (humans have 22 autosome pairs).

Sex chromosomes

X and Y chromosomes; determine sex and carry other genes.

Pedigree

A diagram showing inheritance patterns across generations in a family.

Autosomal Dominant inheritance

One copy of the mutant allele is enough to cause disease; about half of offspring are affected; generations may not be skipped.

Achondroplasia

An autosomal dominant condition; mutation leads to changes in a protein important for skeletal development.

Marfan syndrome

An autosomal dominant connective tissue disorder caused by a mutation affecting elastic collagen.

Huntington’s disease

Autosomal dominant trinucleotide repeat disorder (CAG repeats) causing adult-onset brain degeneration.

Autosomal Recessive inheritance

Two mutant allele copies are required for disease; about 25% of children of carriers are affected; risk increases with consanguinity.

Cystic fibrosis

Autosomal recessive disease due to CFTR gene mutation; defective chloride transport leading to thick mucus.

Sickle cell anemia

Autosomal recessive disease from a single base pair mutation in hemoglobin causing misshapen red blood cells.

X-linked Recessive inheritance

Mutations on the X chromosome; males more often affected; females usually carriers; no father-to-son transmission.

Hemophilia A

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

Duchenne muscular dystrophy

X-linked recessive disorder due to dystrophin gene mutation; progressive muscle degeneration.

Karyotype

A full set of chromosomes used for diagnostic purposes.

Aneuploidy

Abnormal number of chromosomes; monosomies are generally lethal; some trisomies survive.

Down syndrome (Trisomy 21)

Presence of an extra chromosome 21; caused by nondisjunction; maternal age effect; prenatal diagnosis possible.

Nondisjunction

Failure of homologous chromosomes or sister chromatids to separate properly during meiosis.

Prenatal diagnosis

Procedures like amniocentesis (16 weeks) or chorionic villus sampling (9–10 weeks); Quad Screen may accompany testing.

Down syndrome characteristics

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

Monosomy

Loss of one chromosome; autosomal monosomies are lethal.

Trisomy

Presence of an extra chromosome; Down syndrome is Trisomy 21.

Klinefelter syndrome

Sex chromosome aneuploidy: 47,XXY in males.

Turner syndrome

Sex chromosome aneuploidy: 45, X; only monosomy that is not universally lethal.

XXX syndrome

Sex chromosome aneuploidy: 47,XXX.

XYY syndrome

Sex chromosome aneuploidy: 47,XYY.