Leaving Certificate Biology: Genetics, DNA, and Epigenetics

Comprehensive vocabulary review flashcards covering DNA structure, transcription, translation, mutations, epigenetics, and Mendelian/sex-linked genetics from the Leaving Certificate Biology Year Book.

DNA (Deoxyribonucleic Acid)

A double-stranded nucleic acid located inside the nucleus (as well as mitochondria and chloroplasts) that can coil and fold to fit into the cell.

Complimentary Base Pairs

Bases that match or correspond with each other in DNA; adenine pairs with thymine (joined by two weak hydrogen bonds), and guanine pairs with cytosine (joined by three hydrogen bonds).

Double Helix

The twisted ladder-like three-dimensional shape of a DNA molecule.

Gene

A section of DNA that contains the genetic code or instructions for the production of a protein.

Non-coding DNA

DNA sequences (also known as junk DNA) that do not contain the genetic instructions for the formation of a protein.

Genome

All the genetic material present in an organism.

Gene Expression

The process that occurs when the genetic information contained in a gene is actively used to make a protein.

Nucleotide

The basic sub-unit of DNA consisting of a phosphate group, a five-carbon deoxyribose sugar, and a nitrogenous base (adenine, thymine, guanine, or cytosine).

Polynucleotide

A polymer molecule formed from many nucleotides joined together in a chain.

Purines

Double-ringed nitrogen bases, specifically adenine (A) and guanine (G).

Pyrimidines

Single-ringed nitrogen bases, specifically thymine (T) and cytosine (C).

Frances Crick and James Watson

The scientists who discovered the shape and structure of DNA.

Chromosome Composition

Structures located in the nucleus consisting of $60\%$ protein and $40\%$ DNA, where the protein holds the DNA in place.

RNA (Ribonucleic Acid)

A single-stranded nucleic acid containing the sugar ribose and the nitrogenous base uracil instead of thymine, found in the nucleus, cytoplasm, and ribosome.

Non-nuclear DNA

DNA located outside the cell nucleus, consisting of mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA).

Maternal Inheritance of mtDNA

The biological rule stating that mitochondrial DNA is inherited solely from the mother because the mitochondria are located in the collar of the sperm, which does not enter the egg during fertilisation.

Characteristic

An inherited feature that varies among individuals of a species, such as eye colour or hair colour.

Trait

A specific variant of an inherited characteristic, such as green eyes or brown eyes.

Genetic Code

A sequence of three bases (codon or triplet) that represents a code for one of the $20$ common amino acids used in protein synthesis.

Codon (Triplet)

A sequence of three consecutive bases (nucleotides) in DNA or mRNA that codes for a specific amino acid, a start signal, or a stop signal.

Transcription

The anabolic process occurring in the nucleus where mRNA is synthesized from an unwound DNA template strand.

RNA Polymerase

The enzyme responsible for joining RNA bases together to form an mRNA strand during transcription.

Ribosomal RNA (rRNA)

The form of RNA that builds the structural framework of the ribosome and holds mRNA in place via weak bonds during translation.

Transfer RNA (tRNA)

Molecules found in the cytoplasm carrying an anticodon on one end and a corresponding amino acid on the other, responsible for delivering amino acids to the ribosome.

Anticodon

A sequence of three bases on a tRNA molecule that is complementary to a specific codon on an mRNA strand.

Translation

The stage of protein synthesis in the ribosome where the mRNA code is translated into a sequence of amino acids with the help of tRNA.

Globular Proteins

Fully functional proteins that have a heavily folded tertiary shape, such as enzymes.

Fibrous Proteins

Structural proteins that possess very few foldings, such as keratin.

Mutation

A change in the amount or structure of an organism's DNA, usually preventing the correct protein from being produced.

Mutagens

Agents that induce genetic mutations, including ionising radiation (X-rays, UV radiation), chemicals (tobacco smoke, pesticides), and viruses (HPV).

Point Mutation (Gene Mutation)

A change in the nucleotide sequence of a single gene due to incorrect base pairing (deletion, insertion, or substitution) during DNA replication, which is not visible under a light microscope.

Cystic Fibrosis

A human disorder caused by a recessive point mutation in a single gene (homozygous recessive), resulting in a missing protein that leads to thick, sticky mucus accumulation in the lungs and digestive system.

Chromosome Mutation

A significant change in the overall structure or number of chromosomes in a cell.

Chromosomal Inversion

A chromosomal mutation where a broken fragment of a chromosome rotates $180^\circ$ before reattaching to the same chromosome.

Chromosomal Translocation

A chromosomal mutation where a section of a chromosome detaches and attaches itself to a non-homologous chromosome.

Down's Syndrome

A chromosomal mutation caused by an extra copy of chromosome 21 ($2n = 47$), typically resulting from abnormal meiosis.

Turner Syndrome

A human sex chromosome abnormality where a female possesses only one X chromosome instead of two (XO).

Klinefelter Syndrome

A human sex chromosome abnormality where a male carries an additional X chromosome ($XXY$).

Histones

Specific nuclear proteins around which DNA strands wrap tightly to form chromosomal structures.

Chromatin

The elongated, thread-like form of chromosomes present in the nucleus during interphase when the cell is not actively dividing.

Epigenetics

The study of changes in gene expression that alter whether genes are turned 'on' or 'off' without changing the underlying DNA nucleotide sequence.

DNA Methylation

An epigenetic modification where a methyl group attaches directly to DNA to turn off or prevent gene expression.

Histone Modification

An epigenetic mechanism where chemical changes cause DNA to wind too tightly around histones, preventing activation and switching the gene off.

Dutch Hunger Winter (1944–1945)

A historical famine event that triggered epigenetic changes (DNA methylation) in the growth and metabolism genes of unborn children, increasing their adult risk of obesity, diabetes, and heart disease across generations.

Species

A group of similar organisms capable of naturally interbreeding with one another to produce fertile offspring.

Gametes

Haploid sex cells that are capable of fusing during fertilisation to create a diploid zygote.

Alleles

Different or alternative forms of the same gene located at the same locus on homologous chromosomes.

Locus

The precise physical position of a gene on a chromosome.

Dominant Allele

An allele that actively prevents the expression of the corresponding recessive allele in a heterozygote.

Recessive Allele

An allele whose phenotypic expression is blocked or masked whenever a dominant allele is present.

Genotype

The genetic makeup of an organism indicating the specific alleles that are present.

Phenotype

The observable physical characteristics of an organism, determined by its genotype interacting with its environment.

Monohybrid Cross

A genetic cross examining the inheritance patterns of a single characteristic.

Complete Dominance

A genetic condition where the dominant allele completely overrides and masks the recessive allele, ensuring only the dominant phenotype is expressed.

Somatic Cells

All regular diploid body cells of an organism, excluding sex cells or reproductive gametes.

Autosomes

The $44$ non-sex chromosomes found in humans that control traits unrelated to biological sex or gender.

Sex Linkage (X Linkage)

The phenotypic expression of an allele that is located specifically on the X chromosome.

Haemophilia

A sex-linked recessive bleeding disorder caused by the absence of a specific blood-clotting protein, occurring much more frequently in males than females.