Genetics and DNA Fundamentals

Vocabulary-style flashcards covering key concepts from the genetics and DNA notes.

Chargaff's rules

In DNA, adenine equals thymine and cytosine equals guanine (A=T and C=G); the amounts of A and T are the same, as are C and G.

Base pairing

A pairs with T and C pairs with G via hydrogen bonds.

DNA nucleotide composition

Percent composition of A, T, C, G in DNA; A=T and C=G; sums to 100%.

Watson and Crick

Researchers who proposed the double-helix model of DNA structure in 1953.

DNA double helix

Two antiparallel DNA strands wound into a helix, held together by base pairing.

Rosalind Franklin

Scientist whose X-ray diffraction data contributed to the discovery of DNA's structure.

X-ray crystallography

Technique used to determine the arrangement of atoms in a crystal; used to study DNA structure.

Hershey–Chase experiment

Experiment demonstrating that DNA, not protein, is the genetic material in viruses.

Bacteriophage

A virus that infects bacteria.

Sister chromatids

Identical copies of a chromosome connected at the centromere, formed during DNA replication.

Centromere

Region of a chromosome where sister chromatids are held together and spindle fibers attach during division.

Histones

Proteins around which DNA wraps to form nucleosomes; basic proteins involved in DNA packaging.

Nucleotide base

The four DNA bases: adenine (A), thymine (T), cytosine (C), guanine (G).

Hydrogen bonds

Weak bonds between complementary bases (A–T forms 2 bonds; C–G forms 3 bonds) linking the two DNA strands.

Autosomes

Chromosomes that are not sex chromosomes; in humans, chromosomes 1–22; appear the same in males and females.

Sex chromosomes

Chromosomes that determine sex; in humans, X and Y.

Chromosome number

Humans have 46 chromosomes (23 pairs).

Diploid cell

Cell containing two complete sets of chromosomes (2n).

Karyotype

A display of an organism's chromosomes arranged by size/shape; reveals sex and major chromosomal features.

Information inferred from a karyotype

Sex and large-scale chromosomal abnormalities; overall chromosome number and structure.

DNA polymerase

Enzyme that adds nucleotides to a growing DNA strand during replication; synthesizes 5' to 3' and has proofreading.

Primer

A short nucleic acid sequence that provides a starting point for DNA synthesis.

Semiconservative replication

Each new DNA molecule consists of one old strand and one newly synthesized strand.

DNA replication steps: helicase

Enzyme that unwinds/unzips the DNA double helix.

DNA replication steps: primase

Enzyme that lays down RNA primers to start DNA synthesis.

DNA replication steps: DNA polymerase

Enzyme that adds nucleotides to the growing DNA strand.

DNA replication steps: ligase

Enzyme that seals nicks/gaps in the DNA backbone, joining Okazaki fragments.

Mutation

A change in the DNA sequence.

Nucleotide dimers

Pyrimidine dimers (often thymine dimers) formed by UV light, causing DNA damage.

Gene

A DNA sequence that codes for an RNA or protein product and heritable trait.

Gene expression

Process by which information from a gene is used to synthesize a functional product (RNA or protein).

Transcription

Process of copying DNA into messenger RNA (mRNA).

Translation

Process by which ribosomes read mRNA and synthesize a protein using tRNA-delivered amino acids.

DNA vs RNA

DNA: double-stranded, deoxyribose, bases A, T, C, G. RNA: single-stranded, ribose, bases A, U, C, G.

Introns and exons

Introns are noncoding regions removed from RNA; exons are coding regions that remain to form the final mRNA.

mRNA

Messenger RNA; carries genetic information from DNA to ribosomes for protein synthesis.

tRNA

Transfer RNA; delivers amino acids to the ribosome and contains an anticodon.

Substitution

A point mutation where one base is replaced by another.

Insertion

Addition of one or more nucleotides into the DNA sequence; can cause a frameshift.

Deletion

Loss of one or more nucleotides from the DNA sequence; can cause a frameshift.

Frameshift mutation

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

Interphase

Phase of the cell cycle when the cell grows and DNA replicates (G1, S, G2).

Prophase

First stage of mitosis: chromosomes condense, nuclear envelope breaks, spindle forms.

Metaphase

Mitotic stage where chromosomes align at the cell equator; spindle fibers attach to kinetochores.

Anaphase

Mitotic stage where sister chromatids separate and move toward opposite poles.

Telophase

Mitotic stage where nuclei reform and chromosomes decondense; followed by cytokinesis.

Cytokinesis (animals)

Cytoplasmic division in animals; cleavage furrow forms and the membrane pinches inward.

Cytokinesis (plants)

Cytoplasmic division in plants; a cell plate forms to create a separating cell wall.

Crossing over

Exchange of genetic material between homologous chromosomes during meiosis I, increasing diversity.

Homologous chromosomes

Chromosome pairs that are similar in length, shape, and gene sequence; one from each parent.

Tumor / neoplasm

An abnormal mass of tissue resulting from uncontrolled cell growth.

Benign

A non-cancerous tumor that does not invade neighboring tissues.

Malignant

A cancerous tumor that can invade surrounding tissues and spread.

Oncogenes

Genes that promote cancer when mutated or overexpressed; act as the 'gas pedals' of cell division.

Homozygous

Having two identical alleles for a gene.

Heterozygous

Having two different alleles for a gene.

Dominant allele

An allele that masks the effect of the other allele in a heterozygote.

Recessive allele

An allele whose effects are masked in a heterozygote; expressed in homozygotes.

Genotype

An organism's genetic makeup for a trait (the alleles present).

Phenotype

An organism's observable traits or characteristics.

Monohybrid cross

Cross examining the inheritance of a single gene; often yields a 3:1 phenotypic ratio in heterozygotes.

Probability of recessive offspring (Aa x Aa)

25% expected recessive phenotype under complete dominance.

Polygenic inheritance

Traits controlled by multiple genes, often showing continuous variation (e.g., skin color, height).

Pedigree

A diagram showing the inheritance patterns of a trait through generations.

Autosomal dominant

Dominant allele on an autosome; affected individuals have at least one affected parent.

Autosomal recessive

Recessive allele on an autosome; carriers are typically unaffected but can produce affected offspring.

X-linked disorders

Disorders caused by genes on the X chromosome; more common in males due to having a single X.

Nondisjunction

Failure of chromosome pairs to separate properly during meiosis, producing aneuploidies.

Down syndrome

Trisomy 21; three copies of chromosome 21.

Turner syndrome

Monosomy X in females (45,X), resulting in a single X chromosome.