DNA and inheritance

Comprehensive vocabulary flashcards covering Year 10 genetics topics: DNA structure, replication, mutations, gene expression (transcription & translation), cell division (mitosis & meiosis), Mendelian genetics, and sex-linked inheritance.

DNA (Deoxyribonucleic acid)

The genetic material of an organism classified as a nucleic acid, which contains the instructions coding for traits and is identical across all body cells of an individual.

Nucleotide

The monomer subunit of nucleic acids, consisting of a 5-carbon deoxyribose sugar, a negative phosphate group ($\text{PO}_4^{3-}$), and a variable cyclic nitrogenous base.

Polynucleotide

A polymer strand formed by joining nucleotide subunits together through strong sugar-phosphate bonds.

Sugar-Phosphate Backbone

The structural framework of a DNA strand created by strong covalent bonds connecting the deoxyribose sugars and phosphate groups of adjacent nucleotides.

Complementary Base Pairing

The specific pairing rule in DNA where adenine ($\text{A}$) always bonds to thymine ($\text{T}$) and guanine ($\text{G}$) always bonds to cytosine ($\text{C}$).

Chargaff's Rule

The principle stating that in a double-stranded DNA molecule, the amount of adenine equals thymine ($\text{A} = \text{T}$) and the amount of guanine equals cytosine ($\text{G} = \text{C}$).

Hydrogen Bond

A relatively weak chemical bond formed between complementary nitrogenous bases that holds the two antiparallel strands of a DNA double helix together.

Gene

A specific segment of DNA that codes for a functional protein or trait, functioning as a basic unit of heredity passed from parents to offspring.

Genome

The complete set of genetic material and genes present within an organism.

Chromosome

A condensed, organized structure located in the nucleus of eukaryotic cells, each composed of a single tightly coiled DNA molecule.

Chromatid

One of two identical longitudinal halves of a replicated chromosome, containing one molecule of DNA and connected to its sister chromatid at the centromere.

Centromere

The specialized DNA region of a duplicated chromosome where two sister chromatids are held together.

Karyotype

A visual profile or image of an individual's complete set of chromosomes, arranged and paired by size, centromere position, and banding pattern.

Linked Genes

Genes that are located on the same chromosome and tend to be inherited together.

Autosomes

Chromosomes that do not determine the biological sex of an organism; humans possess $44$ autosomes ($22$ pairs).

Sex Chromosomes

The pair of chromosomes responsible for determining the biological sex of an individual ($\text{XX}$ for females, $\text{XY}$ for males).

Homologous Chromosomes

A pair of matching chromosomes with similar genes and length, where one chromosome is inherited from the mother and one from the father.

Somatic Cell

Any typical body cell of an organism that is not involved in sexual reproduction and contains a full diploid set of chromosomes.

Gamete

A reproductive sex cell (sperm or ovum) containing a single haploid set of chromosomes ($n = 23$ in humans).

Diploid Cell ($2n$)

A cell containing two complete sets of homologous chromosomes ($46$ chromosomes in humans), with one set derived from each parent.

Haploid Cell ($n$)

A cell that possesses only one single set of unpaired chromosomes ($23$ chromosomes in humans), typical of gametes.

Down Syndrome (Trisomy 21)

A chromosomal condition resulting from an extra copy of chromosome $21$, giving individuals $47$ total chromosomes in somatic cells.

Gene Expression

The multi-step biological process by which information encoded in DNA is used to direct protein synthesis via transcription and translation.

RNA (Ribonucleic Acid)

A single-stranded nucleic acid composed of ribose sugar, a phosphate group, and nitrogenous bases with uracil ($\text{U}$) replacing thymine ($\text{T}$).

Transcription

The synthesis of an mRNA molecule from a DNA template strand, occurring within the nucleus of eukaryotic cells.

RNA Polymerase

The primary enzyme in transcription that unwinds DNA by breaking hydrogen bonds and synthesizes a complementary mRNA strand using RNA nucleotides.

Messenger RNA (mRNA)

A single-stranded RNA molecule transcribed from DNA that travels through nuclear pores to the cytoplasm to deliver protein assembly instructions to ribosomes.

Translation

The synthesis of a polypeptide protein chain at a ribosome by decoding the sequence of codons on an mRNA transcript.

Transfer RNA (tRNA)

An RNA molecule responsible for bringing specific amino acids to the ribosome, matching its anticodon to complementary codons on mRNA.

Codon

A sequence of three consecutive nucleotides on an mRNA molecule that corresponds to a single specific amino acid or a stop signal.

Anticodon

A triplet sequence of bases on a tRNA molecule that base-pairs complementarily with a specific codon on an mRNA strand.

Genetic Code Redundancy

The property of the genetic code where multiple distinct codon sequences can code for the exact same amino acid.

Start Codon

The specific triplet codon $\text{AUG}$ on mRNA that initiates translation and specifies the amino acid methionine.

Stop Codon

One of three mRNA codons ($\text{UAA}$, $\text{UAG}$, or $\text{UGA}$) that signals the termination of translation and triggers polypeptide release.

DNA Replication

The biological process occurring during interphase where a cell creates an exact duplicate copy of its entire DNA prior to cell division.

Semi-Conservative Replication

The mode of DNA replication where each newly formed double-stranded DNA molecule retains one original template strand and one newly synthesized strand.

DNA Helicase

The enzyme that unwinds the double helix and unzips DNA strands during replication by breaking the hydrogen bonds between base pairs.

DNA Polymerase

The enzyme that synthesizes new DNA strands by aligning and binding complementary free nucleotides to the exposed template strands.

Mutation

A permanent, heritable change in the base sequence or quantity of genetic material (DNA) in an organism.

Point Mutation

A genetic mutation involving an alteration, insertion, or deletion of a single nucleotide base in a DNA sequence.

Substitution Mutation

A type of point mutation where one nucleotide base in a DNA sequence is exchanged for a different base.

Insertion Mutation

A mutation characterized by the addition of one or more extra nucleotides into a DNA sequence, shifting the reading frame.

Deletion Mutation

A mutation involving the loss or removal of one or more nucleotides from a DNA sequence, altering the subsequent reading frame.

Silent Mutation

A point mutation that alters a codon but does not change the resulting amino acid sequence, leaving protein function unchanged.

Missense Mutation

A point mutation where a base substitution alters the codon so that it codes for a different amino acid, potentially changing protein structure and function.

Nonsense Mutation

A point mutation that prematurely substitutes a normal amino acid codon with a stop codon, producing a truncated, non-functional protein.

Frameshift Mutation

A mutation caused by insertion or deletion of nucleotides that shifts the translational reading frame of three-base codons down the entire gene.

Mutagen

An environmental agent (such as radiation, UV light, or chemicals) that increases the baseline frequency of genetic mutations.

Sickle Cell Disease

A genetic disorder caused by a single base substitution in the hemoglobin gene, replacing glutamic acid with valine and leading to rigid, crescent-shaped red blood cells.

Mitosis

A form of nuclear division in somatic cells that produces two genetically identical diploid ($2n$) daughter cells from one parent cell for growth and tissue repair.

Cytokinesis

The physical cleavage and division of a parent cell's cytoplasm into two distinct daughter cells following mitosis.

Meiosis

A specialized two-step cell division process occurring in germ-line cells that produces four genetically distinct haploid ($n$) gametes.

Independent Assortment

The random orientation and alignment of maternal and paternal homologous chromosome pairs along the cell equator during meiosis I, creating genetic variation in gametes.

Crossing Over

The reciprocal exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis I, generating recombinant chromatids.

Allele

An alternate form or variant of a particular gene occupying the same locus on homologous chromosomes.

Dominant Allele

An allele whose phenotypic trait is expressed whenever at least one copy is present, masking the effect of a recessive allele.

Recessive Allele

An allele whose phenotypic trait is only expressed when two copies are present ($\text{homozygous}$) and is masked by a dominant allele in heterozygous individuals.

Genotype

The specific combination of alleles an individual possesses for a particular gene (such as $\text{DD}$, $\text{Dd}$, or $\text{dd}$).

Phenotype

The observable physical or behavioural traits of an organism, determined by its genotype and environmental interactions.

Homozygous

Possessing two identical alleles for a specific gene locus (either homozygous dominant, e.g., $\text{DD}$, or homozygous recessive, e.g., $\text{dd}$).

Heterozygous

Possessing two different alleles for a specific gene locus (e.g., $\text{Dd}$), often acting as a carrier for a recessive trait.

Sex-Linked Inheritance

The transmission of genetic traits or disorders controlled by genes located on the sex chromosomes (most commonly the X chromosome).

X-Linked Recessive Trait

A condition governed by a recessive gene on the X chromosome that disproportionately affects biological males because they possess only one X chromosome and lack a masking dominant allele.

X-Linked Dominant Trait

A genetic condition caused by a dominant gene on the X chromosome that affects females more frequently than males because females inherit two X chromosomes.