Genetics & Cell Biology Study Guide

Vocabulary flashcards covering cell cycle stages, mitosis, meiosis, Mendelian inheritance, chromosome theory, sex determination, and chromosomal mutations based on the Genetics & Cell Biology Study Guide.

$G_1$ (Gap 1) Phase

The stage of interphase characterized by cell growth, organelle replication, and active protein synthesis.

S (Synthesis) Phase

The stage of interphase during which exact semi-conservative DNA replication occurs and duplicate chromosomes are synthesized.

$G_2$ (Gap 2) Phase

The stage of interphase involving final preparation for mitosis and the synthesis of proteins required for cell division.

Checkpoints

Regulatory control mechanisms that ensure critical cellular steps are completed correctly before the cell proceeds to the next phase, such as the $G_1/S$, $G_2/M$, and Spindle Assembly (M) checkpoints.

Prophase (Mitosis)

The mitotic stage in which chromosomes condense, the mitotic spindle forms, and the nucleolus disappears.

Prometaphase (Mitosis)

The mitotic stage during which the nuclear envelope breaks down and spindle microtubules attach to kinetochores.

Metaphase (Mitosis)

The mitotic stage where individual chromosomes align along the metaphase plate.

Anaphase (Mitosis)

The mitotic stage where sister chromatids separate and move toward opposite spindle poles.

Telophase (Mitosis)

The mitotic stage where nuclear envelopes reform, chromosomes decondense, and the mitotic spindle dissolves.

Centromere

An essential structural element of a functional eukaryotic chromosome that serves as the attachment site for kinetochores and spindle fibers, necessary for proper chromosome segregation.

Telomeres

Repeated DNA sequences located at the ends of eukaryotic chromosomes that protect them against degradation and end-fusion.

Origins of Replication

Specific DNA sequences on a chromosome where DNA replication initiates.

Archaea

Prokaryotic organisms possessing a circular chromosome and lacking a nuclear membrane, distinguished from bacteria by having histone-like proteins complexed with their DNA.

Synapsis

The precise pairing of homologous chromosomes during Prophase I of meiosis.

Crossing Over (Recombination)

A process occurring during Prophase I of meiosis where homologous chromosomes exchange genetic segments, generating genetic variation.

Independent Assortment

A principle stating that alleles at different loci separate independently of one another during gamete formation, occurring during Metaphase I and Anaphase I of meiosis.

Spermatogenesis

The process in male animals where a diploid spermatogonium undergoes mitosis and differentiates into a primary spermatocyte, undergoing Meiosis I and II to continuously yield four equal, functional haploid sperm.

Oogenesis

The process in female animals where a diploid oogonium becomes a primary oocyte (arrested in Prophase I) and divides via meiosis to yield one large functional haploid ovum and non-functional polar bodies due to unequal cytoplasmic division.

Microsporogenesis

Male gamete formation in plants where diploid microsporocytes undergo meiosis to form four microspores, each dividing by mitosis to form pollen grains containing a tube cell and a generative cell.

Megasporogenesis

Female gamete formation in plants where a megasporocyte undergoes meiosis to produce four megaspores (three degenerate), and the surviving megaspore undergoes three rounds of mitosis to form an 8-nucleate embryo sac.

Preformationism

A historical theory proposing that a fully formed miniature human (homunculus) exists inside the egg or sperm, requiring only mitosis for growth without any role for meiosis in genetic shuffling.

Genotype

The specific set of alleles possessed by an organism (e.g., $RR$, $Rr$).

Phenotype

The observable physical or physiological characteristic or trait of an organism (e.g., orange fruit, cream fruit).

Principle of Segregation

Mendel's principle stating that diploid organisms possess two alleles for a trait, which separate during gamete formation so that each gamete carries only one allele.

Blending Inheritance

An early hypothesis proposing that parental traits mix irreversibly like paints, disproved by Mendel's demonstration of discrete, particulate inheritance.

Concept of Dominance

The principle that when two different alleles for a trait are present in a heterozygote, only the dominant allele is expressed in the phenotype, masking the recessive allele.

Multiplication Rule

A probability rule used to determine the probability of two or more independent events occurring together: $P(A \text{ and } B) = P(A) \times P(B)$.

Addition Rule

A probability rule used to calculate the probability of any one of two or more mutually exclusive events occurring: $P(A \text{ or } B) = P(A) + P(B)$.

Chromosome Theory of Heredity

The biological principle stating that genes are located at specific sites (loci) on physical chromosomes, grounding Mendelian inheritance in microscopic and cellular biology.

Chi-Square Goodness-of-Fit Test

A statistical test that evaluates whether observed offspring ratios significantly deviate from expected Mendelian ratios, where the P-value indicates the probability that differences arose by chance alone.

Barr Body

An inactivated, condensed X chromosome visible in the interphase nuclei of somatic cells of female or multi-X individuals.

Lyon Hypothesis

The hypothesis stating that X-chromosome inactivation occurs randomly early in embryonic development to achieve dosage compensation between males and females.

Chromosome Rearrangements

A category of chromosome mutations involving structural alterations in chromosomes, including duplications, deletions, inversions, and translocations.

Aneuploidy

A category of chromosome mutations involving alterations in the number of individual chromosomes within a set.

Polyploidy

A category of chromosome mutations involving changes in the number of complete sets of chromosomes (e.g., $3n$, $4n$).

Position Effect

The alteration of gene expression caused by relocating a gene sequence relative to regulatory sequences or heterochromatin via inversions or translocations.

Nullisomy

A type of aneuploidy characterized by the loss of both chromosomes of a homologous pair, represented as $2n - 2$.

Monosomy

A type of aneuploidy characterized by the loss of a single chromosome, represented as $2n - 1$.

Trisomy

A type of aneuploidy characterized by the gain of a single extra chromosome, represented as $2n + 1$.

Tetrasomy

A type of aneuploidy characterized by the gain of two homologous extra chromosomes, represented as $2n + 2$.