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Anaphase
The fourth stage of M phase. As anaphase proceeds, half of the chromosomes move to one pole, and the other half move to the other pole.
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Asexual Reproduction
A form of reproductiopn that does not involve the union of gametes; at the cellular level, a preexisting cell divides to produce two new cells.
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Autosomes
Chromosomes that are not sex chromosomes.
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Binary Fission
The physical process whereby a bacterial cell divides into two daughter cells. During this event, the two daughter cells become divided by the formation of a septum.
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Bivalent
A structure in which two pairs of homologous sister chromatids have synapsed (aligned) with each other.
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Cell Cycle
In eukaryotic cells, a series of stages through which a cell progresses in order to divide. The phases are G for growth, S for synthesis (of the genetic material), and M for mitosis. There are two G phases, G1 and G2.
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Cell Plate
The structure that forms between two daughter plant cells that leads to the separation of the cells by the formation of an intervening cell wall.
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Centromere
A segment of eukaryotic chromosomal DNA that provides an attachment site for the kinetochore.
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Centrosomes
A cellular structure from which microtubules emanate.
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Chiasma
The site where crossing over occurs between two chromosomes. It resembles the Greek Letter chi, X
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Chromatid
Following chromosomal replication in eukaryotes, the two copies remain attached to each other in the form of sister chromatids.
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Sister Chromatids
Pairs of replicated chromosomes that are attached to each other at the centromere. Sister chromatids are genetically identical to each other.
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Chromosome Theory of Inheritance
A theory of Sutton and Boveri, which indicated that the inheritance patterns of traits can be explained by the transmission patterns of chromosomes during gametogenesis and fertilization.
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Chromosomes
The structures within living cells that contain the genetic material. Genes are pysically located within the structure of chromosomes. Biochemically, chromosomes contain a very long segment of DNA, which is the genetic material, and proteins, which are bound to the Dna and provide it with an organized structure.
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Cleavage Furrow
A constriction that causes the division of two animal cells during cytokinesis.
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Diakinesis
The fifth stage of prophase of meiosis I
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Diplotene
The fourth stage of prophase of meiosis I
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Embryo Sac
In flowering plants, the female gametophyte that contains an egg cell.
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Endosperm
In flowering plants, the material in the seed, which is 3n, that nourishes the developing embryo.
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Gametogenesis
The production of gametes.
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Gametophyte
the haploid generation of plants
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Hemizygous
Describes the single copy of an X-linked gene in the male. A male mammal is said to be hemizygous for X-linked genes.
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Heterogametic sex
In a species with two types of sex chromosomes, the heterogametic sex produces two types of gametes. For example, in mammals, the male is the heterogametic sex, because a sperm can contain either an X or a Y chromosome.
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Heterogamous
Describes a species that produces two morphologically different types of gametes.
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Holandric Genes
A gene on the Y chromosome
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Homogametic sex
In a species with two types of sex chromosomes, the homogametic sex produces only one type of gamete.
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Homologues
One of the chromosomes in a pair of homologous chromosomes.
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Karyotype
A photographic representation of all the chromosomes within a cell. It reveals how many chromosomes are found within an actively dividing somatic cell.
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Kinetochore
A group of cellular proteins that attach to the centromere during meiosis and mitosis.
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Interphase
The series of phases G1, S, and G2, during which a cell spends most of its life.
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Isogamous
Describes a species that makes morphologically similar gametes.
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Leptotene
The first stage of prophase of meiosis I.
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Locus
A physical location of a gene within a chromosome.
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Meiosis
A form of nuclear division in which the sorting process results in the production of haploid cells from a diploid cell.
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Metaphase
The third stage of M phase. The chromosomes align along the center of the spindle apparatus, and the formation of the spindle apparatus is complete.
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Metaphase plate
The plane at which chromosomes align during metaphase.
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Mitosis
A type of nuclear division into two nuclei, such that each daughter cell will receive the same complement of chromosomes.
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Mitotic spindle Apparatus
The structure that organizes and separates the chromosomes during M phase of the eukaryotic cell cycle.
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Nucleoid
A darkly staining region that contains the genetic material of mitochondria, chloroplasts, or bacteria.
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Oogenesis
the production of egg cells
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organelles
A large specialized structure within a cell, which is often surrounded by a single or double membrane.
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Pachytena
The third stage of prophase of meiosis I
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Pollen Grain
The male gametophyte of flowering plants.
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Prometaphase
The second phase of M phase. During this phase, the nuclear membrane vesiculates, and the mitotic spindle is completely formed.
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Prophase
The first stage of M phase. The chromosomes have already replicated and begin to condense. The mitotic spindle starts to form.
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Pseudoautosomal inheritance
The inheritance pattern of genes that are found on both the X and Y chromosomes. Even though such genes are located physically on the sex chromosomes, their pattern of inheritance is identical to that of autosomal genes.
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Reciprocal cross
A pari of crosses in which the traits of the two parents differ with regard to sex. For example, one cross could be a red-eyed female fly and a white-eyed male fly, and the reciprocal cross would be a red-eyed male fly and a white-eyed female fly.
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Restriction point
A point in the G1 phase of the cell cycle that causes a cell to progress to cell division.
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Sex chromosomes
A pair of chromosomes that determines sex in a species.
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Sex linkage
The phenomenon that certain genes are found on one of the two types of sex chromosomes but not both.
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sporophyte
The diploid generation of plants
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Synapsis
The event in which homologous chromosomes recognize each other and then align themselves along their entire lengths.
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Synaptonemal Complex
A complex of proteins that promote the interconnection between homolgous chromosomes during meiosis.
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Telophase
The fifth stage of M phase. The chromosomes have reached their respective poles and decondense.
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Testcross
An experimental cross between a recessive individual and an individual whose genotype the experimenter wishes to determine.
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Tetrad
1. The association among four sister chromatids during meiosis. 2. a group of four fungal spores contained within an ascus.
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X-Linked alleles
Genes that are physically located within the X chromosome.
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X-linked inheritance
An inheritance pattern in certain species that involves genes that are located only on the X chromosome.
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Zygotene
the second stage of prophase of meiosis I.
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