Chapter 9: Producing Gametes

Autosome

A chromosome that is the same in both males and females of a species; autosomes do not include sex chromosomes

Sex chromosome

A chromosome that affects sexual traits; are different in male and female individuals of the same species

Meiosis

A special type of cell division in sexually reproducing organisms that reduces the chromosome number by half

Diploid

Describes a cell or organism that has a genome comprising two copies of each chromosome, represented by 2n

Haploid

Describes a cell or organism that has a genome that contains one copy of each chromosome, represented by n

Interphase

The stage of the cell cycle between active divisions

Prophase

The first stage of meiosis where chromosomes condense and centrioles form

Synapsis

The physical pairing of homologous chromosomes

Metaphase

The second stage of meiosis where chromosomes line up at the equator of the cell

Metaphase plate

The equator of the cell where chromosomes line up during metaphase

Anaphase

The third stage of meiosis where chromosomes separate to opposite poles of the cell

Disjunction

The segregation of chromosomes to separate poles of the cell during anaphase

Telophase

The fourth stage of meiosis where membranes form around the two new nuclei

Cytokinesis

The division of the cytoplasm and formation of new cell membranes

Germ cell

A cell that produces gametes

Bivalent

Visible chromosomes in a cell during prophase I of meiosis, which are made up of two homologous chromosomes joined together

Chiasma

The point of contact between homologous chromosomes during prophase I of meiosis

Crossing over

An event during meiosis in which homologous chromosomes exchange segments with one another

Independent assortment

The process by which the paternal and maternal chromosomes of each homologous pair behave independently of the other homologous pairs as they separate in meiosis I

Ovum

The female haploid reproductive cell; also called an egg

Oogenesis

The process in the ovary that produces female gametes (ovum/egg)

Oogonia

The stem cells responsible for producing cells that can create eggs

Primary oocyte

A cell that enters meiosis I in oogenesis

Secondary oocyte

A cell produced by meiosis I that enters meiosis II in oogenesis

Polar body

A small structure containing a nucleus and very little cytoplasm that is produced, dies and is absorbed by the ovary during oogenesis

Spermatogenesis

The continuous production of sperm cells in the testis

Spermatogonia

The stem cells responsible for producing cells that can create sperm

Primary spermatocyte

A cell that enters meiosis I in spermatogenesis

Secondary spermatocyte

A cell produced by meiosis I that enters meiosis II in spermatogenesis

Spermatid

A haploid daughter cell of spermatogenesis

Deletions

A section of DNA is lost from a chromosome, causing genes to be missing and potentially leading to serious disorders, developmental problems or non-viable offspring

Inversions

A section of DNA breaks off and reattaches in reverse order, usually causing mild or no effects because the genes are still present

Duplications

A section of DNA is copied twice, creating extra copies of genes that can cause overactive genes and developmental or health problems

Translocations

A section of DNA breaks off and attaches to a different chromosome, which can have mild or serious effects depending on the genes involved

Aneuploidy

When a cell contains an abnormal number of chromosomes for its species, either more or fewer chromosomes than normal

Non-disjunction

A pair of chromosomes fails to separate during anaphase, with both members of the pair moving to the same pole of the cell

Euploid

A cell that contains the normal number of chromosomes for its species, either n haploid or 2n diploid