Cell Division, Meiosis, and Principles of Genetic Variation Flashcards

Comprehensive practice flashcards covering cellular division, the mechanics of mitosis and meiosis, genetic variation principles (Independent Assortment, Law of Segregation), and chromosomal nondisjunction errors.

S Phase

A period in the cell cycle known for DNA replication, ensuring every cell in the human body contains the exact same DNA.

Cell Differentiation

The process by which genetically identical cells become different (e.g., brain cells vs. blood cells) through the production of specific proteins.

Diploid ($2n$)

A state where a cell contains two full sets of chromosomes; in humans, mitosis begins and ends with cells in this state.

Metaphase Plate (Mitosis)

A single file of individual replicated chromosomes with sister chromatids attached during the middle stage of mitosis.

Spindle Fibers

Structures composed of microtubules that pull sister chromatids apart during anaphase.

Homologous Chromosomes

Pairs of chromosomes that share the same genes in the same sequence but possess different versions (alleles) of those genes.

Alleles

Different versions of a gene, often differing by only a few base pairs and amino acids.

Synapsis

The process in meiosis I where homologous chromosomes pair up to form a tetrad.

Tetrad

A structure formed during synapsis consisting of four strands of DNA: $2$ sister chromatids from the paternal chromosome and $2$ from the maternal chromosome.

Crossing Over (Homologous Recombination)

An exchange of chromosomal parts occurring at points called chiasma, creating new gene combinations not present in the parents.

Chiasma

The specific point (plural: chiasmata) where DNA strands intertwine and exchange parts during crossing over.

Independent Assortment

The principle that the orientation of each tetrad on the metaphase I plate is random and independent of other tetrads.

Anaphase I

The stage of meiosis I where homologous chromosomes separate, resulting in haploid ($1n$) cells.

Anaphase II

The stage of meiosis II where sister chromatids finally separate.

Law of Segregation

The genetic principle stating that diploid parents produce haploid gametes carrying only one allele per gene.

Genotype

The specific combination of alleles for a gene, such as $Aa$.

Locus

The specific location of a gene on a chromosome.

Nondisjunction

An error where chromosomes fail to segregate properly during meiosis I (homologs) or meiosis II (sister chromatids).

Monosomy

A condition of having one missing chromosome; autosomal types and Monosomy Y are embryonic lethal.

Turner Syndrome

A survivable phenotype resulting from Monosomy X (a missing sex chromosome).

Trisomy

A condition of having one extra chromosome ($n + 1$); most autosomal types are embryonic lethal except for Trisomy $21$.

Down Syndrome (Trisomy $21$)

A survivable trisomy because chromosome $21$ is the smallest chromosome with the fewest genes.

Klinefelter Syndrome

A sex chromosome abnormality characterized by an $XXY$ genotype.

XXX Syndrome

A sex chromosome variance characterized by a low impact phenotype and an $XXX$ genotype.

XYY Syndrome

A sex chromosome variance characterized by a low impact phenotype and an $XYY$ genotype.