Chapters 7–10: Genetics, Molecular Biology, Cell Reproduction, and Patterns of Inheritance

Comprehensive practice flashcards testing key vocabulary across DNA structure, replication, gene expression, transcription, translation, cell division (mitosis and meiosis), and Mendelian and human genetics.

Bacteriophage

A virus that infects bacteria, consisting of a DNA genome encased in a protein coat with a hollow sheath and tail fibers; used by Hershey and Chase to confirm DNA as hereditary material.

DNA Nucleotide

A monomer unit of DNA consisting of a five-carbon sugar (deoxyribose), three phosphate groups, and one nitrogen-containing base (adenine, thymine, guanine, or cytosine).

Chargaff's Rules

The principle that the bases of the two DNA strands in a double helix pair in a consistent way: adenine pairs with thymine ($\text{A}-\text{T}$) and cytosine pairs with guanine ($\text{C}-\text{G}$), while relative proportions of $\text{A}$ and $\text{G}$ vary among species.

Histone

A protein spool around which DNA wraps at regular intervals inside a eukaryotic chromosome.

Diploid

Having two of each type of chromosome characteristic of a species ($2n$); for example, a normal human body cell contains 46 chromosomes.

Karyotype

An image showing an individual's complement of chromosomes arranged by size, length, shape, and centromere location.

Sister Chromatid

One of two attached, identical DNA molecules of a duplicated eukaryotic chromosome.

Centromere

The constricted region of a eukaryotic chromosome where sister chromatids are attached.

Autosomes

Paired chromosomes that share the same length, shape, centromere location, and genes, consisting of all chromosomes in a cell other than the sex chromosomes (22 pairs in humans).

Sex Chromosomes

Members of a pair of chromosomes that differ between males and females ($XY$ and $XX$ in humans; $ZW$ in birds).

Semiconservative Replication

The mechanism of DNA replication in which each newly formed double helix consists of one conserved parental strand and one newly assembled strand.

DNA Polymerase

A replication enzyme that uses an existing DNA strand as a template to assemble a new, complementary strand of DNA from free nucleotides.

Primer

A short, single strand of DNA that base-pairs with a targeted DNA sequence to initiate DNA synthesis by DNA polymerase.

DNA Ligase

An enzyme that seals breaks and nicks in the sugar-phosphate backbone of double-stranded DNA to produce a continuous strand.

Mutation

A permanent change in the nucleotide sequence of an organism's DNA.

Gene

A distinct DNA sequence that encodes an RNA or protein product through its specific sequence of nucleotide bases ($\text{A}$, $\text{T}$, $\text{G}$, $\text{C}$).

Transcription

The enzymatic process in which RNA polymerase uses a gene's DNA sequence as a template to synthesize a complementary strand of RNA.

Translation

The cytoplasmic process in which the base sequence of an mRNA molecule is decoded into a polypeptide chain of amino acids.

Gene Expression

The multi-step process by which the genetic information encoded within a gene is converted into a functional structural or catalytic product (an RNA or protein).

Promoter

A specific DNA sequence situated near the start of a gene that serves as the binding site for RNA polymerase to initiate transcription.

Exons

Nucleotide sequences in eukaryotic pre-mRNA that are retained and spliced together during RNA processing to form the mature mRNA.

Introns

Intervening nucleotide sequences in pre-mRNA that are excised and removed during RNA processing before translation.

Codon

A set of three consecutive nucleotide bases in mRNA that specifies a particular amino acid or serves as a translational start or stop signal.

Genetic Code

The set of 64 triplet mRNA codons that specify the 20 naturally occurring amino acids as well as translational start and stop signals.

Transfer RNA (tRNA)

An RNA molecule that delivers specified amino acids to the ribosome during translation; contains an anticodon triplet and an amino acid attachment site.

Base-Pair Substitution

A type of gene mutation in which a single base pair is replaced with a different base pair; an example is the sickle-cell anemia mutation altering the beta globin gene.

Differentiation

The process by which cells become specialized in form and function as cell lineages begin to transcribe different subsets of their genes.

Transcription Factor

A regulatory protein that binds directly to DNA to enhance or suppress the rate of transcription.

Master Gene

A gene that produces a product directing the expression of numerous other genes to coordinate an intricate developmental task, such as eye development.

Homeotic Gene

A type of master gene that governs the structural formation and anatomical positioning of specific body parts during embryonic development.

Gene Knockout

A research method used to study gene function by experimentally inactivating or deleting a gene entirely.

Barr Body

A tightly condensed, transcriptionally inactive X chromosome visible within the somatic cells of mammalian females.

Dosage Compensation

The theoretical mechanism by which X chromosome inactivation equalizes the expression of X-linked genes between mammalian females ($XX$) and males ($XY$).

SRY Gene

The master gene located on the human Y chromosome that triggers the formation of testes and male sex determination.

Epigenetics

Heritable changes in gene expression and cellular phenotype that do not involve alterations to the underlying DNA sequence.

Mitosis

A nuclear division mechanism that allocates a complete, identical set of chromosomes to two new nuclei, maintaining the chromosome number in daughter cells.

Cell Cycle

The recurring sequence of events spanning the formation of a eukaryotic cell through interphase, mitosis, and cytoplasmic division.

Interphase

The interval of the eukaryotic cell cycle between mitotic divisions when a cell grows, doubles cytoplasmic components, and copies its DNA ($G_1$, $S$, and $G_2$ stages).

Homologous Chromosomes

A pair of chromosomes that possess the same length, shape, centromere location, and genes, with one chromosome inherited from the maternal parent and one from the paternal parent.

Cleavage Furrow

A groove produced during animal cell cytoplasmic division as an ATP-energized contractile ring of microfilaments deepens and pinches the cell in two.

Cell Plate

A disk-shaped partition formed by the fusion of Golgi-derived vesicles along the division plane that matures into dividing cross-walls in plant cells.

Tumor Suppressors

Checkpoint gene products (such as BRCA1, BRCA2, and p53) that halt the cell cycle or inhibit mitosis when DNA is damaged or replication is incomplete.

Neoplasm

An abnormal accumulation of dividing cells that have escaped normal cell cycle controls.

Oncogene

A mutated gene that actively helps transform a normal cell into a tumor cell; typically converted from a normal proto-oncogene.

Metastasis

The process by which malignant cells break free from a primary tumor, travel through blood or lymph vessels, and establish new tumor sites in other tissues.

Telomeres

Repetitive, noncoding DNA sequences capping the terminal ends of eukaryotic chromosomes that protect coding DNA from degradation during successive replication cycles.

Alleles

Alternative forms of the same gene that differ slightly in nucleotide sequence and encode slightly different versions of the gene product.

Meiosis

A two-stage nuclear division process that shuffles alleles and halves the chromosome number from diploid ($2n$) to haploid ($n$) to produce four gamete nuclei.

Crossing Over

The exchange of corresponding DNA segments between nonsister chromatids of homologous chromosomes during prophase I of meiosis, creating new allele combinations.

Zygote

The diploid ($2n$) cell produced by the fusion of two haploid ($n$) gametes at fertilization, representing the first cell of a new sexually reproducing individual.

Homozygous

Having identical alleles of a gene on both homologous chromosomes (such as $PP$ or $pp$).

Heterozygous

Carrying two different alleles of a gene on homologous chromosomes (such as $Pp$).

Genotype

The particular set of alleles carried in the genome of an individual.

Phenotype

An individual's observable physical, biochemical, or behavioral traits resulting from genotype and environmental interaction.

Testcross

A breeding cross between an individual with a dominant phenotype (and unknown genotype) and an individual known to be homozygous recessive to identify the unknown genotype.

Monohybrid Cross

A cross between individuals with different alleles of a single gene, typically resulting in a $3:1$ phenotypic ratio among $F_2$ offspring under complete dominance.

Dihybrid Cross

An experimental cross between individuals with different alleles of two distinct genes, yielding a classic $9:3:3:1$ phenotypic ratio among $F_2$ offspring.

Independent Assortment

Mendel's principle stating that alleles of genes on nonhomologous chromosomes are distributed into gametes independently of one another during meiosis.

Incomplete Dominance

A pattern of inheritance in which one allele is not fully dominant over another, resulting in a heterozygous phenotype that is an intermediate blend between the two homozygous phenotypes.

Codominance

An inheritance pattern in which two nonidentical alleles are both fully expressed in heterozygous individuals, as observed in human $AB$ blood type.

Pleiotropy

The genetic effect in which a single gene influences multiple, distinct phenotypic traits (e.g., mutations involved in sickle-cell anemia or Marfan syndrome).

Polygenic Inheritance

The pattern of inheritance in which a single trait is governed by the additive or combined products of multiple genes (e.g., coat color in Labrador retrievers or human skin color).

Pedigree

A standardized family chart illustrating the phenotypes and relationships of family members across multiple generations to study human inheritance patterns.

Genetic Abnormality

An uncommon variant of an inherited trait that does not cause harm or mild/severe medical problems (e.g., polydactyly).

Genetic Disorder

A heritable condition that produces a recognizable syndrome of mild or severe medical complications (e.g., cystic fibrosis or achondroplasia).

Nondisjunction

The failure of homologous chromosome pairs or sister chromatids to separate normally during mitotic or meiotic division.

Down Syndrome (Trisomy 21)

The only human autosomal trisomy that allows individuals to survive into adulthood, caused by having three copies of chromosome 21.