Grade 8 Life Science - Genetics & Heredity Unit Master Study Guide

Vocabulary practice flashcards covering cell hierarchy, DNA structure, protein synthesis, gene mutations, reproductive modes, Mendelian and non-Mendelian genetics, and inheritance mechanisms.

Cellular Hierarchy

The structural levels of genetic organization within an organism: $\text{Cell} \rightarrow \text{Nucleus} \rightarrow \text{Chromosome} \rightarrow \text{DNA} \rightarrow \text{Gene} \rightarrow \text{Protein}$.

Nucleus

The control center of eukaryotic cells that houses all genetic blueprints (DNA).

DNA (Deoxyribonucleic Acid)

A long, double-stranded molecule shaped like a twisted ladder (Double Helix).

Rungs ("Steps of Ladder")

The internal steps of the DNA double helix formed by paired nitrogenous bases.

Complementary Base Pairing Rule

The biological rule stating that Adenine pairs strictly with Thymine ($A - T$) and Cytosine pairs strictly with Guanine ($C - G$).

Replication

The cellular process occurring in the nucleus that copies the complete DNA genome ($\text{DNA} \rightarrow \text{DNA}$) before a cell divides during cell division.

Transcription

The process occurring in the nucleus where the DNA gene sequence is unzipped and copied into single-stranded messenger RNA ($\text{DNA} \rightarrow \text{mRNA}$).

Translation

The process occurring at the ribosome in the cytoplasm where the ribosome reads the mRNA base sequence to assemble amino acids into functional proteins ($\text{mRNA} \rightarrow \text{Protein}$).

Gene Expression

The cellular mechanism of turning specific genes "ON" or "OFF," allowing specialized cells (e.g., skin, muscle, or brain cells) with identical DNA to carry out distinct functions.

Mutagens

Physical or chemical agents that directly alter DNA sequences, such as X-rays, UV radiation/high heat, harmful chemicals, and certain viruses.

Gene Mutation

A permanent change in the nucleotide base sequence of DNA or chromosome structure.

Harmful Mutations

Mutations that cause defective proteins, leading to genetic disorders such as Cystic Fibrosis or Progeria.

Beneficial Mutations

Mutations that provide useful adaptations enhancing survival, such as the Apolipoprotein AI-Milano mutation that lowers cholesterol.

Neutral / Silent Mutations

Mutations that cause no functional change in phenotype, occurring at an average rate of approximately $60$ new point mutations inherited by humans.

Homologous Chromosomes

Matching pairs of chromosomes carrying genes for the exact same physical traits at identical locations (loci).

Human Chromosome Inventory

The standard set of $46$ total chromosomes in human body cells organized into $23$ homologous pairs ($23$ inherited from the maternal egg and $23$ from the paternal sperm).

Asexual Reproduction

A mode of reproduction involving $1$ parent and no gametes that produces uniform ($100\%$ identical) offspring through simple cellular copying.

Sexual Reproduction

A mode of reproduction involving $2$ parents (male and female) whose gametes (egg and sperm) each carry half the DNA to produce offspring with high genetic variation.

Binary Fission

A form of asexual reproduction in single-celled organisms, such as bacteria and amoeba, where the cell splits in half.

Budding

A form of asexual reproduction in organisms such as Hydra and sponges where clone offspring sprout directly from the parent.

Zygote

A fertilized cell with $2$ copies of each chromosome resulting from the fusion of a sperm ($1$ copy) and an egg ($1$ copy).

Allele

A specific variant or version of a gene, represented by letters such as $T$ or $t$.

Dominant Allele

An allele that masks recessive traits, represented by a capital letter (such as $T$).

Recessive Allele

An allele masked by dominant alleles that is only physically expressed when two copies are present ($tt$), represented by a lowercase letter (such as $t$).

Homozygous Dominant

A genotype consisting of two identical dominant alleles inherited for a trait (e.g., $TT$, also known as purebred dominant).

Homozygous Recessive

A genotype consisting of two identical recessive alleles inherited for a trait (e.g., $tt$, also known as purebred recessive).

Heterozygous

A genotype consisting of one dominant allele and one recessive allele inherited for a trait (e.g., $Tt$, also known as a hybrid or carrier).

Genotype

The specific allele combination or genetic code of an organism for a particular trait (e.g., $Tt$).

Phenotype

The observable physical expression or appearance of a trait resulting from an organism's genotype (e.g., tall plant).

Complete Dominance

An inheritance pattern in which the dominant allele completely hides the effect of the recessive allele in heterozygous individuals (e.g., $Bb = \text{Black Dog}$).

Incomplete Dominance

A non-Mendelian inheritance pattern where neither allele is dominant, resulting in a heterozygous genotype that produces an intermediate, blended phenotype (e.g., $RR \times WW \rightarrow RW = \text{Pink}$).

Codominance

A non-Mendelian inheritance pattern where both alleles are fully expressed simultaneously without blending (e.g., Erminette speckled chickens, Roan cattle, or human AB blood type).

Sex Chromosomes

The chromosomes responsible for biological sex determination, where human females carry two X chromosomes ($XX$) and males carry one X and one Y chromosome ($XY$).

X-Linked Recessive Diseases

Disorders caused by mutated genes located strictly on the X chromosome (e.g., Hemophilia), affecting males far more frequently because they have only one X chromosome and lack a second copy to mask the mutation.

Carrier

An individual who possesses one copy of a recessive mutated allele (e.g., female $X^h X$ or heterozygous $Aa$) without exhibiting symptoms of the genetic disorder.

Autosomal Recessive Inheritance

A pattern of inheritance where two unaffected carrier parents ($Aa \times Aa$) each transmit a recessive disease allele, giving offspring a $25\%$ chance of inheriting genotype $aa$ and expressing the disorder.