AP Biology Unit 5: Meiosis and Genetic Diversity

Meiosis

A specialized type of cell division that reduces the number of chromosomes by half and produces four gamete cells.

Gametes

Haploid reproductive cells (sperm and egg in animals) that carry one set of chromosomes (n).

Somatic Cells

Diploid body cells that carry two sets of chromosomes (2n).

Homologous Chromosomes

A pair of chromosomes, one from each parent, that carry genes for the same traits at the same loci.

Sister Chromatids

Identical copies of a chromosome attached at the centromere, formed during DNA replication.

Diploid (2n)

A cell containing two full sets of chromosomes.

Haploid (n)

A cell containing only one single set of chromosomes.

Prophase I

The first stage of Meiosis I where chromosomes condense and homologous chromosomes undergo synapsis.

Metaphase I

Stage in Meiosis I where homologous pairs align at the metaphase plate.

Anaphase I

Stage in Meiosis I where homologous chromosomes separate and move toward opposite poles.

Telophase I

Stage in Meiosis I where the cell divides into two daughter cells, each haploid but with sister chromatids still attached.

Meiosis II

The second round of meiosis where sister chromatids are separated, functioning mechanistically like mitosis.

Prophase II

The first stage of Meiosis II where the spindle apparatus forms and no DNA replication occurs.

Metaphase II

Stage in Meiosis II where individual chromosomes align at the metaphase plate.

Anaphase II

Stage in Meiosis II where sister chromatids are separated and pulled to opposite poles.

Telophase II

Final stage in Meiosis II where four genetically unique haploid daughter cells are produced.

Crossing Over

The exchange of DNA segments between nonsister chromatids during Prophase I, creating recombinant chromosomes.

Independent Assortment

The random orientation of homologous chromosome pairs at the metaphase plate during Metaphase I.

Random Fertilization

The process by which any sperm can fuse with any egg, increasing genetic variation.

PMAT

A mnemonic for the stages of cell division: Prophase, Metaphase, Anaphase, Telophase.

Interphase

The phase before meiosis begins, consisting of G1, S, and G2 stages where DNA is replicated.

Tetrad

A structure containing four chromatids formed during synapsis in Prophase I.

Chiasmata

Linkage points where crossing over occurs between homologous chromosomes.

Nuclear Envelope

The membrane that encloses the nucleus, which breaks down during Prophase I.

Equational Division

The type of division that occurs during Meiosis II, resembling mitosis.

Ploidy

The number of sets of chromosomes in a cell, diploid (2n) or haploid (n).

S Phase

The stage of Interphase where DNA is replicated to form sister chromatids.

Genetic Diversity

The variation in genes among individuals which is enhanced by meiosis through crossing over, independent assortment, and random fertilization.