VCE Biology Unit 2: Inheritance, Genetics, and Genomes

Comprehensive vocabulary flashcards covering key definitions, chromosomal structures, dominance mechanisms, epigenetics, and inheritance models for VCE Biology Unit 2 Area of Study 1.

Gene

A specific sequence of DNA that encodes for a functional product (such as a protein) through its nucleotide base sequence, determining a particular trait and passed from parent to offspring.

Allele

An alternative or different form of a particular gene that occupies the same gene locus on a chromosome (e.g., brown versus blue eye colour).

Gene Locus

The specific physical position or location of a particular gene on a chromosome (plural: loci).

Genotype

The specific combination of alleles that an individual possesses for a particular gene, represented using letters (such as $AA$, $Aa$, or $aa$).

Phenotype

The observable physical characteristics or features of an organism, resulting from the interaction between its genotype and environmental influences.

Homozygous

Having two identical alleles for a particular gene locus (e.g., homozygous dominant $AA$ or homozygous recessive $aa$).

Heterozygous

Having two different alleles for a particular gene locus (e.g., $Aa$).

Genome

The complete set of genetic information in an organism or population, measured in the number of base pairs contained in a haploid set of chromosomes.

Genomics

The study of the structure, function, evolution, mapping, and editing of genomes, used to study genetic diseases and compare relatedness between species.

Human Genome Project

An international scientific research project from 1990 to 2003 that successfully determined the sequence of the approximately three billion base pairs that make up the human genome.

Complete Dominance

A pattern of inheritance in which the dominant allele completely masks the phenotypic expression of the recessive allele in heterozygous individuals.

Incomplete Dominance

A pattern of inheritance where neither allele is completely dominant over the other, causing heterozygous individuals to display a blended, intermediate third phenotype (such as pink flowers $C^R C^W$ resulting from red $C^R C^R$ and white $C^W C^W$ parents).

Codominance

A pattern of inheritance where both alleles are simultaneously and separately expressed in the heterozygote to produce a distinct third phenotype (such as roan calves $C^W C^R$ showing both red and white hairs).

ABO Blood Groups

A human blood group system determined by multiple alleles ($I^A$, $I^B$, and $i$) that control the presence of surface antigens on red blood cells, wherein $I^A$ and $I^B$ are codominant to each other and dominant over recessive $i$.

Multiple Alleles

A situation where three or more alternative forms of a gene exist within a population (such as the alleles determining ABO blood type in humans or coat colour in rabbits and cats).

Monogenic Trait

A characteristic or trait that is controlled primarily by a single gene locus, typically displaying discontinuous variation (distinct categories).

Polygenic Trait

A characteristic or trait that is determined by the cumulative action of multiple genes, resulting in continuous variation across a spectrum (such as human height or skin pigmentation).

Chromosome

An organised package of DNA condensed around histone proteins, located within the cell nucleus and carrying specific genetic instructions.

Histones

Proteins that DNA wraps tightly around in coils to condense and organise into chromatin.

Centromere

The specialised chromosomal structure that holds two sister chromatids together and serves as the attachment site for spindle fibres during cell division.

Telomeres

Protective caps of repeating DNA sequences located at the ends of chromosomes that safeguard genetic data; discovered by Australian scientist Elizabeth Blackburn.

Homologous Chromosomes

A pair of matching chromosomes of the same length and banding pattern that carry the same gene loci, with one copy inherited from each parent.

Autosomes

Any chromosome that exists as a homologous pair in sexually reproducing organisms and is not directly involved in determining biological sex (chromosomes 1 through 22 in humans).

Sex Chromosomes

The 23rd pair of human chromosomes ($X$ and $Y$) that carry the genes responsible for determining the biological sex of an individual.

X-linked Trait

A trait or condition governed by a gene located exclusively on the $X$ chromosome, capable of being expressed in both biological males and females.

Y-linked Trait

A trait or condition governed by a gene located exclusively on the $Y$ chromosome, which can only be inherited and expressed by biological males.

Carrier

An individual who has inherited a recessive allele for a genetic trait or disease without phenotypically displaying it, because it is masked by a dominant allele.

Diploid ($2n$)

Describing cells (such as somatic cells) containing two complete sets of chromosomes: one paternal copy and one maternal copy ($2n = 46$ in humans).

Haploid ($n$)

Describing specialised reproductive cells (gametes) containing only one single set of chromosomes with no homologous pairs ($n = 23$ in humans).

Gamete

A specialised haploid sex cell (sperm in males or ovum in females) produced through meiosis that combines during fertilisation to form a diploid zygote.

Epigenetics

The study of heritable and chemical changes that regulate gene expression (turning genes on or off) without altering the underlying nucleotide base sequence of DNA.

DNA Methylation and Histone Acetylation

Key epigenetic mechanisms where adding methyl groups ($-\text{CH}_3$) to DNA condenses it to silence genes, whereas adding acetyl groups ($-\text{COCH}_3$) to histones relaxes DNA coils to activate gene transcription.

Gene Imprinting

An epigenetic phenomenon whereby only one inherited parental copy of a gene (either maternal or paternal) is actively expressed, while the other copy is suppressed via mechanisms such as DNA methylation.

Linked Genes

Genes located close together on the same chromosome that tend to be inherited together as a unit into the same gamete rather than assorting independently.

Unlinked Genes

Genes located on completely different chromosomes or positioned far apart on the same chromosome, allowing them to assort independently during meiosis.

Crossing Over

The reciprocal exchange of genetic segments between non-sister chromatids of homologous chromosomes during Prophase I of meiosis, creating new allele combinations (recombinants).

Independent Assortment

The random orientation and segregation of homologous chromosome pairs at the cell equator during Metaphase I of meiosis, producing genetic diversity in the resulting gametes.

Map Unit

A unit used to measure the relative genetic distance between linked genes on a chromosome, where $1\text{ map unit}$ represents a $1\%$ recombination frequency.

Monohybrid Cross

A genetic mating experiment used to analyse the inheritance patterns and offspring ratios of a single gene locus.

Dihybrid Cross

A genetic mating experiment used to predict the phenotypic and genotypic ratios of offspring for two different genes simultaneously.

Test Cross

A genetic cross between an organism showing a dominant phenotype (with an unknown genotype) and a homozygous recessive individual, performed to determine if the unknown is homozygous dominant or heterozygous.

Pedigree Chart

A standardized family tree diagram displaying the occurrence and inheritance of a specific phenotype or genetic disorder across multiple generations.

Aneuploidy

A chromosomal condition characterised by an atypical number of chromosomes, caused by the gain or loss of specific individual chromosomes.

Trisomy

A type of aneuploidy in which a diploid cell or organism gains an extra copy of a chromosome, possessing three copies instead of the typical homologous pair (e.g., Trisomy 21).