DNA & Genetics - Vocabulary Flashcards

Key terms and definitions spanning DNA structure, transcription/translation, inheritance patterns, and cell division.

DNA

Double-stranded, helical molecule that stores genetic information; polymer of nucleotides.

Nucleotide

Monomer of DNA composed of a deoxyribose sugar, a phosphate group, and a nitrogenous base.

Deoxyribose

Five-carbon sugar used in DNA nucleotides.

Phosphate group

Phosphate component of a nucleotide linking sugar to form DNA backbone.

Adenine (A)

Nitrogenous base that pairs with Thymine in DNA (2 hydrogen bonds).

Thymine (T)

Nitrogenous base that pairs with Adenine in DNA (2 hydrogen bonds).

Guanine (G)

Nitrogenous base that pairs with Cytosine in DNA (3 hydrogen bonds).

Cytosine (C)

Nitrogenous base that pairs with Guanine in DNA (3 hydrogen bonds).

Complementary base pairing

Rule that A pairs with T and C pairs with G through hydrogen bonds.

Chromosome

Thread-like DNA-protein structure; tightly wound DNA; visible during cell division; humans have 46 in somatic cells.

Chromatin

DNA wrapped around histones; condenses into chromosomes.

Histone

Protein around which DNA winds to form chromatin.

Telomere

Protective repetitive DNA caps at the ends of chromosomes.

Centromere

Region where sister chromatids are held together and where spindle fibers attach during cell division.

Sister chromatids

Two identical copies of a chromosome that are held together at the centromere after DNA replication.

Gene

DNA segment that codes for the synthesis of a protein.

Homologous chromosome

Pair of chromosomes with the same genes at the same loci, one from each parent.

Karyotype

Image of an organism’s chromosomes arranged by size and banding patterns.

Autosomes

Non-sex chromosomes (chromosomes 1–22 in humans).

Heterosomes / Sex chromosomes

Chromosomes that determine sex (X and Y in humans).

Diploid (2n)

Cell with two sets of chromosomes; somatic cells in humans.

Haploid (n)

Cell with one set of chromosomes; gametes in humans.

Gamete

Sex cell (sperm or egg) that carries half the genetic information.

Somatic cell

Body cell; typically diploid.

Allele

Different form of a particular gene.

Dominant allele

Allele expressed in the phenotype whenever present.

Recessive allele

Allele expressed only when homozygous recessive.

Genotype

Genetic makeup; the combination of alleles for a gene.

Phenotype

Observable trait resulting from genotype and environment.

Homozygous

Two identical alleles for a gene.

Heterozygous

Two different alleles for a gene.

Autosomal dominant

A trait where a dominant allele on an autosome expresses in the phenotype; affected individuals may have affected parents.

Autosomal recessive

A trait expressed only when two recessive alleles are present on autosomes.

Codominance

Both alleles are expressed equally in the phenotype.

Sex-linked (X-linked) inheritance

Genes on the X chromosome; males are often hemizygous for these genes.

Hemizygous dominant

Male has only one X chromosome carrying the dominant allele, determining phenotype.

Hemizygous recessive

Male has only one X chromosome carrying the recessive allele, determining phenotype.

Pedigree

Diagram showing family relationships and how traits are inherited across generations.

Punnett square

Tool to predict possible genotypes and phenotypes of offspring from parental alleles.

Start codon (AUG)

Codon that signals the start of translation and codes for Methionine.

Stop codons

UAA, UAG, UGA; terminate translation and do not code for amino acids.

Codon

Triplet of mRNA bases that specifies an amino acid.

mRNA

Messenger RNA; transcribes DNA and carries codons to the ribosome.

tRNA

Transfer RNA; brings specific amino acids to the ribosome during translation.

rRNA

Ribosomal RNA; structural and catalytic component of the ribosome.

Transcription

First stage of protein synthesis; synthesis of mRNA from DNA; occurs in the nucleus; RNA polymerase unzips DNA and copies a gene into mRNA.

Translation

Second stage of protein synthesis; mRNA is read by the ribosome in the cytoplasm to assemble amino acids into a polypeptide; tRNA brings amino acids.

Protein synthesis

Process of building proteins via transcription and translation.

Amino acid

Building blocks of proteins; 20 standard amino acids encoded by codons.

Ribosome

Molecular machine where translation occurs; reads mRNA codons and assembles amino acids.

DNA replication

Before cell division, DNA is copied; semi-conservative process where each new DNA molecule contains one old and one new strand.

DNA helicase

Enzyme that unwinds and separates the DNA strands.

DNA polymerase

Enzyme that adds new nucleotides to form a new DNA strand.

Semi-conservative replication

Each new DNA molecule contains one original strand and one newly synthesized strand.

Mitosis

Cell division of somatic (body) cells producing two genetically identical diploid daughter cells.

Meiosis

Cell division that produces four haploid gametes with genetic variation.

Interphase

Phase where cells grow and DNA is replicated before division.

Prophase

Chromosomes condense and become visible; spindle forms.

Metaphase

Chromosomes align at the cell equator.

Anaphase

Chromatids separate and move to opposite poles.

Telophase

Nuclei reform around separated chromosomes.

Cytokinesis

Division of the cytoplasm, yielding two separate cells.

Down syndrome (Trisomy 21)

Chromosomal abnormality where there are three copies of chromosome 21.

X chromosome count and female/male gender

Females: XX; Males: XY; X carries many genes; Y carries few.

Sex determination ratio (pedigree context)

Genotypic/phenotypic outcomes for offspring based on parental sex-linked genes.

X-linked inheritance example: colour blindness

Recessive X-linked trait; males can be affected with a single recessive allele on their single X.