Meiosis and Genetic Variation

Vocabulary practice flashcards covering the stages of meiosis, chromosome numbers, haploid vs. diploid states, and sources of genetic variation.

Sexual reproduction

A form of reproduction that combines gametes from two parents.

Gametes

Reproductive cells, such as sperm and egg, that contain half the number of chromosomes found in normal body cells.

Zygote

A cell formed when two gametes unite at fertilization, containing genetic information from both parents and restoring the normal diploid chromosome count.

Meiosis

A specialized type of cell division containing two rounds of division without intervening DNA replication, reducing the chromosome count by half to produce four haploid cells from one diploid cell.

Homologous chromosomes

Pairs of matching chromosomes—one inherited from the mother and one from the father—that carry the same genes but may contain different alleles.

Alleles

Alternate forms of genes located on homologous chromosomes.

Diploid ($2n$)

A cell containing a full set of chromosomes, where $n$ is the number of sets; characteristic of most human body cells.

Haploid ($n$)

A cell containing only one set of chromosomes, such as a gamete (sperm or egg cell).

Sister chromatids

Two identical copies of a chromosome produced during DNA replication prior to the start of meiosis.

Meiosis I

The first division of meiosis, during which homologous chromosome pairs align, undergo crossing over, and separate into two haploid cells.

Meiosis II

The second division of meiosis, where sister chromatids are separated without prior DNA replication, yielding four haploid daughter cells.

Prophase I

The first phase of meiosis I in which homologous chromosomes pair up, crossing over occurs, the spindle forms, chromosomes condense, and the nuclear envelope dissolves.

Crossing over

A process unique to meiosis occurring during prophase I where segments of DNA are exchanged between non-sister chromatids of homologous chromosomes, creating new allele combinations.

Metaphase I

The phase of meiosis I where homologous chromosome pairs randomly align along the center of the cell and attach to the spindle fibers.

Anaphase I

The phase of meiosis I in which homologous chromosome pairs are separated and moved toward opposite poles of the cell.

Telophase I

The phase of meiosis I where spindle fibers dissolve, followed by cytokinesis to produce two haploid cells without reforming a complete nuclear envelope.

Cytokinesis

The division of the cell cytoplasm that follows telophase after each division round in meiosis.

$2^{23}$ (Over 8 million)

The total number of possible different chromosome combinations in a single human gamete due to the random separation of 23 chromosome pairs during meiosis I.