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Biology 2e

Key Terms

Biology 2eKey Terms
alternation of generations
life-cycle type in which the diploid and haploid stages alternate
chiasmata
(singular, chiasma) the structure that forms at the crossover points after genetic material is exchanged
cohesin
proteins that form a complex that seals sister chromatids together at their centromeres until anaphase II of meiosis
crossover
exchange of genetic material between nonsister chromatids resulting in chromosomes that incorporate genes from both parents of the organism
fertilization
union of two haploid cells from two individual organisms
gametophyte
a multicellular haploid life-cycle stage that produces gametes
germ cells
specialized cell line that produces gametes, such as eggs or sperm
interkinesis
(also, interphase II) brief period of rest between meiosis I and meiosis II
life cycle
the sequence of events in the development of an organism and the production of cells that produce offspring
meiosis
a nuclear division process that results in four haploid cells
meiosis I
first round of meiotic cell division; referred to as reduction division because the ploidy level is reduced from diploid to haploid
meiosis II
second round of meiotic cell division following meiosis I; sister chromatids are separated into individual chromosomes, and the result is four unique haploid cells
recombination nodules
protein assemblies formed on the synaptonemal complex that mark the points of crossover events and mediate the multistep process of genetic recombination between nonsister chromatids of a homologous pair
reduction division
nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division
somatic cell
all the cells of a multicellular organism except the gametes or reproductive cells
spore
haploid cell that can produce a haploid multicellular organism or can fuse with another spore to form a diploid cell
sporophyte
a multicellular diploid life-cycle stage that produces haploid spores by meiosis
synapsis
formation of a close association between homologous chromosomes during prophase I
synaptonemal complex
protein lattice that forms between homologous chromosomes during prophase I, supporting crossover
tetrad
two duplicated homologous chromosomes (four chromatids) bound together by chiasmata during prophase I
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