TETRAD: A four-part structure that forms during the prophase of meiosis and consists of two
homologous chromosomes, each composed of two sister chromatids.
A homologous chromosome is a set of one maternal chromosome and one paternal chromosome
that pair up with each other inside a cell during meiosis.
Synapsis (also called syndesis) is the pairing of two homologous chromosomes that occurs
during meiosis.
Chromosomal crossover (or crossing over) is the exchange of genetic material between homologous chromosomes that results in
recombinant chromosomes. It is one of the final phases of genetic recombination, which occurs duringprophase I of meiosis (pachytene) during
a process calledsynapsis.
Nondisjunction ("not coming apart") is the failure of chromosome pairs to separate properly
during meiosis stage 1 or stage 2, specifically in the anaphase.
Genetic recombination:
the process or act of exchanges of genes between chromosomes, resulting in a different genetic
combination and ultimately to the formation of unique gametes with chromosomesthat are different from
those in parents.
 MEIOSIS RESULTS IN RECOMBINATION (mitosis does NOT)
3 ways recombination can occur:
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1.) Independent assortment of Chromosomes: Chromosomes line up randomly on the metaphase plate during meiosis.
2.) Crossing Over: Segments of DNA on the chromatids can switch with that of other chromatids, usually when the chromosomes are
in tetrads during meiosis.
3.) Random Fertilization: A random egg matches with a random sperm.
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