Genes and Genetic Diseases

Vocabulary flashcards covering key terms from the lecture notes on DNA, RNA, and genetic diseases.

DNA

Deoxyribonucleic acid; the genetic material in cells, a double-stranded helix composed of deoxyribose sugar, phosphate backbone, and four bases (A, T, C, G) with A–T and C–G base pairing.

RNA

Ribonucleic acid; usually single-stranded, contains ribose sugar, and bases A, U, C, G; functions in transcription and translation to synthesize proteins.

Deoxyribose

Five-carbon sugar used in DNA (lacks an oxygen at the 2' position compared with ribose in RNA).

Phosphate backbone

The repeating phosphate-sugar backbone of DNA and RNA that provides structural integrity to the nucleic acid strand.

Purines

Double-ring nitrogenous bases; in DNA: adenine (A) and guanine (G).

Pyrimidines

Single-ring nitrogenous bases; in DNA: cytosine (C) and thymine (T). (In RNA, thymine is replaced by uracil.)

Adenine

Purine base that pairs with thymine in DNA (A–T) and with uracil in RNA (A–U).

Thymine

Pyrimidine base in DNA that pairs with adenine (T–A).

Cytosine

Pyrimidine base that pairs with guanine (C–G).

Guanine

Purine base that pairs with cytosine (G–C).

Uracil

Pyrimidine base in RNA that pairs with adenine (U–A); replaces thymine in RNA.

Codon

A three-nucleotide sequence in mRNA that specifies a particular amino acid or a stop signal during translation.

Start codon

The codon (AUG) that signals the beginning of translation and codes for methionine.

Stop codon

Codons (UAA, UAG, UGA) that signal termination of translation.

Triplet

A group of three nucleotides in DNA or RNA that encodes a single amino acid (synonymous with codon in mRNA context).

Genetic code

The universal set of codon-to-amino-acid mappings used by almost all organisms to translate mRNA into a protein; includes start and stop signals.

DNA replication

Semi-conservative process by which DNA is copied prior to cell division, producing two identical DNA molecules.

DNA polymerase

Enzyme that synthesizes new DNA strands by adding nucleotides to a growing chain during replication.

Promoter

DNA sequence where RNA polymerase binds to start transcription.

RNA polymerase

Enzyme that synthesizes RNA from a DNA template during transcription.

Transcription

Process of synthesizing RNA from a DNA template, producing a pre-mRNA transcript.

mRNA

Messenger RNA; carries the encoded genetic information from DNA to the ribosome for protein synthesis.

Cap (5' cap)

A modified guanine nucleotide added to the 5' end of eukaryotic mRNA to protect it and aid ribosome binding.

Poly-A tail

A stretch of adenine nucleotides added to the 3' end of mRNA to stabilize the transcript and aid export from the nucleus.

Exon

Coding sequences in RNA that are retained after splicing to form the mature mRNA.

Intron

Non-coding sequences in RNA that are removed during splicing.

Gene splicing

Process of removing introns and joining exons to form a continuous, functional mRNA.

Translation

Process by which the ribosome reads mRNA codons to synthesize a polypeptide, using tRNA to bring amino acids.

tRNA

Transfer RNA; adaptor molecule that delivers specific amino acids to the ribosome during translation.

Anticodon

Three-nucleotide sequence on tRNA that is complementary to a corresponding mRNA codon.

Ribosome

Molecular machine where translation occurs; composed of large and small subunits and moves along mRNA.

Cap

See 5' cap; protective and ribosome-recognition feature added to mRNA.

Locus

The fixed position of a gene on a chromosome.

Allele

A different form of a gene at a given locus.

Genotype

The genetic constitution at a specific locus or across the genome; the set of alleles an organism carries.

Phenotype

The observable traits or characteristics of an organism, resulting from genotype and environment.

Homozygous

Having two identical alleles at a given locus.

Heterozygous

Having two different alleles at a given locus.

Dominant

Allele whose trait is observable in heterozygotes; mask recessive allele.

Recessive

Allele whose trait is masked in heterozygotes and only expressed in homozygous form.

Carrier

An individual who carries a disease allele but is phenotypically normal (often heterozygous for an autosomal recessive condition or X-linked carrier).

Autosomes

The first 22 pairs of chromosomes; homologous in both sexes.

Sex chromosomes

The 23rd chromosome pair; determines sex (XX in females, XY in males).

Haploid

Having one complete set of chromosomes (n).

Diploid

Having two complete sets of chromosomes (2n).

Euploid

Cells with a multiple of the normal haploid chromosome number (includes haploid and diploid; normal multiples).

Aneuploidy

Abnormal number of chromosomes not a multiple of 23; often due to nondisjunction.

Nondisjunction

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

Trisomy

Having three copies of a particular chromosome in a diploid cell.

Monosomy

Having only one copy of a particular chromosome in a diploid cell.

Down syndrome

Autosomal trisomy of chromosome 21; about 1 in 800 live births; risk increases with maternal age.

Trisomy X

Sex chromosome aneuploidy: female with three X chromosomes (47,XXX); often mild or no obvious symptoms.

Turner syndrome

Sex chromosome aneuploidy: female with a single X chromosome (45,XO); features include short stature and absent/underdeveloped ovaries.

Klinefelter syndrome

Sex chromosome aneuploidy: male with extra X chromosome (47,XXY); features include tall stature, reduced fertility.

Cri du Chat syndrome

Deletion of part of the short arm of chromosome 5; cat-like cry, microcephaly, distinctive features.

Deletion

Loss of a chromosome segment.

Duplication

Presence of a repeated segment or gene sequence on a chromosome.

Inversion

Chromosomal rearrangement where a segment is reversed end to end.

Translocation

Interchange of material between non-homologous chromosomes; includes reciprocal and Robertsonian forms.

Reciprocal translocation

Exchange of segments between two non-homologous chromosomes.

Robertsonian translocation

Fusion of the long arms of two acrocentric chromosomes with loss of the short arms.

Fragile sites

Chromosomal regions prone to gaps or breaks; many are not disease-related.

Fragile X syndrome

X-linked intellectual disability disorder; females may be carriers with variable expression; more severe in males.

Centromere

Region of a chromosome essential for movement during cell division; location types include metacentric, submetacentric, and acrocentric.

Chromatid

One of the two identical halves of a replicated chromosome.

Metacentric

Chromosome with centromere near the middle of the chromosome.

Submetacentric

Chromosome with centromere off-center, creating unequal arm lengths.

Acrocentric

Chromosome with centromere near one end.

Pedigree

Diagram showing family relationships and inheritance of a genetic trait or disease.

Proband

The first individual in a family diagnosed with a genetic disorder used to start a pedigree.

Penetrance

Proportion of individuals with a genotype who express the phenotype; incomplete penetrance means some do not express it.

Expressivity

Extent of phenotype variation among individuals with the same genotype.

Recurrence risk

Probability that the parents of an affected child will have another child with the same condition.

X-linked disorders

Genetic disorders on the X chromosome; more often affect males; affected males cannot pass to sons but can pass to daughters.