Meiosis

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somatic cell

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a body cell that refers to all cells in the body except the sex cells

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gamete

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reproductive cell in an organism

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homologous

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describing "matched" chromosomes that are the two copies of the same chromosome (one from each parent) that carries the same genes

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crossing over

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The exchange of segments of non-sister chromatids between a pair of homologous chromosomes that occurs during meiosis I.

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chiasma

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In early prophase I, when the process of crossing over between non-sister chromatids in a pair of homologus chromosomes form an X-shaped structure.

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cytokinesis

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Division of the cytoplasm to form two daughter cells. Typically occurs immediately after division of the nucleus by mitosis or meiosis.

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prophase I

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Early prophase I:
Chromosomes condense, nuclear envelope breaks up, spindle apparatus forms. Synapsis of homologus chromosomes.

Late prophase I:
Crossing over of non-sister chromatids (often multiple crossovers between the same chromatids).

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metaphase I

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Migration of tetrads to metaphase plate is complete. Prepared to separate.

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anaphase I

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Homologs separate and begin moving to opposite sides of the cell.

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telophase I

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Chromosomes move to opposite sides of the cell, then the cell divides.

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prophase II

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Spindle apparatus forms

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metaphase II

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Chromosomes line up at middle of cell

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anaphase II

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Sister chromatids separate, begin moving to opposite side of cell.

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telophase II

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Chromosomes move to opposite sides of cell, then cell devides

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asexual reproduction

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Any form of reproduction resulting in offspring that are genetically identical to the parent

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sexual reproduction

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Any form of reproduction in which genes from two parents are combined via fusion of gametes, producing offspring that are genetically distinct from both parents.

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clones

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A lineage of genetically individuals or cells

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Diploid

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a cell containing two sets of chromosomes.

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haploid

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a cell with only one set of chromosomes.

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polyploid

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a cell containing two or more paired sets of chromosomes.

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synapsis

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pairing of homologous chromosomes in prophase I

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tetrad

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A four-part structure that forms during the prophase of meiosis and consists of two homologous chromosomes, each composed of two sister chromatids

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sister chromatid

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are generated when a single chromosome is replicated into two copies of itself

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non-sister chromatid

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These chromatids are located on different chromosomes within the same DNA

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Genetic Recombination

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The process by which two strands of genetic material are spliced together, creating new strands with sections of material from each original strand. In meiosis, genetic recombination occurs between homologous chromosomes.

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Self-Fertilization

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The process by which an organism may recombine its own genetic material through meiosis, resulting in an offspring with only one parent.

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Outcrossing

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The process of bringing new genetic material into a population by introducing _relatively_ unrelated parent. This can be by means of introducing any different individual when opposed to self-fertilization, or, more generally, by introducing a member of a different subspecies or breed.

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Trisomy

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The state of an organism having three copies of a chromosome (two from one parent and one from another). In meiosis, trisomy occurs if two homologous chromosomes fail to separate after crossover. In humans, trisomy of various chromosomes can lead to miscarriages or genetic disorders.

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Monosomy

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The state of an organism having only one copy of a chromosome (missing the copy from one parent). In meiosis, monosomy occurs if two homologous chromosomes fail to separate after crossover. It is the complement of trisomy.

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Deleterious

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Describes a genetic trait that is harmful to an individual's or a population's success. Such traits are eventually either removed from a population by evolution, or result in the species extinction.

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Aneuploidy

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The state of having the wrong number of chromosomes. Includes both mono- and trisomy. Caused by non-disjunction between homologous chromosomes.