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Definition
| Alternative form of a gene—alleles occur at the same locus on homologous chromosomes. |
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Term
| Alteration of generations |
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Definition
| Life cycle, typical of land plants, in which a diploid sporophyte alternates with a haploid gametophyte. |
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Definition
| Individual whose chromosome number is not an exact multiple of the haploid number for the species. |
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Definition
| Dark-staining body (discovered by M. Barr) in the nuclei of female mammals that contains a condensed, inactive X chromosome. |
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Definition
| Homologous chromosomes, each having sister chromatids that are joined by a nucleoprotein lattice during meiosis; also called a tetrad. |
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Definition
| Exchange of segments between nonsister chromatids of a bivalent during meiosis. |
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Term
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Definition
| Change in chromosome structure in which the end of a chromosome breaks off or two simultaneous breaks lead to the loss of an internal segment; often causes abnormalities—e.g., cri du chat syndrome. |
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Term
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Definition
| Cell condition in which two of each type of chromosome are present. |
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Definition
| Change in chromosome structure in which a particular segment is present more than once in the same chromosome. |
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Term
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Definition
| Cells containing only complete sets of chromosomes. |
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Definition
| Fusion of sperm and egg nuclei, producing a zygote that develops into a new individual. |
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Term
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Definition
| Haploid sex cell; e.g., egg and sperm. |
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Term
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Definition
| Development of the male and female sex gametes. |
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Term
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Definition
| Haploid generation of the alternation of generations life cycle of a plant; produces gametes that unite to form a diploid zygote. |
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Term
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Definition
| Process in which chromosomes are broken and rejoined to form novel combinations; in this way offspring receive alleles in combinations different from their parents. |
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Definition
| Member of a pair of chromosomes that are alike and come together in synapsis during prophase of the first meiotic division; a homologue. |
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Term
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Definition
| Alleles of unlinked genes segregate independently of each other during meiosis so that the gametes contain all possible combinations of alleles. |
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Term
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Definition
| Period of time between meiosis I and meiosis II during which no DNA replication takes place. |
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Term
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Definition
| Change in chromosome structure in which a segment of a chromosome is turned around 180°; this reversed sequence of genes can lead to altered gene activity and abnormalities. |
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Term
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Definition
| Chromosomes arranged by pairs according to their size, shape, and general appearance in mitotic metaphase. |
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Term
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Definition
| Type of nuclear division that occurs as part of sexual reproduction, in which the daughter cells receive the haploid number of chromosomes in varied combinations. |
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Term
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Definition
| One less chromosome than usual. |
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Term
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Definition
| Production of eggs in females by the process of meiosis and maturation. |
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Term
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Definition
| In oogenesis, a nonfunctional product; two to three meiotic products are of this type. |
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Term
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Definition
| In oogenesis, the functional product of meiosis I; becomes the egg. |
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Term
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Definition
| Reproduction involving meiosis, gamete formation, and fertilization; produces offspring with chromosomes inherited from each parent with a unique combination of genes. |
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Term
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Definition
| Production of sperm in males by the process of meiosis and maturation. |
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Term
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Definition
| Asexual reproductive or resting cell capable of developing into a new organism without fusion with another cell, in contrast to a gamete. |
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Term
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Definition
| Diploid generation of the alternation of generations life cycle of a plant; produces haploid spores that develop into the haploid generation. |
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Term
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Definition
| Pairing of homologous chromosomes during meiosis I. |
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Term
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Definition
| Movement of a chromosomal segment from one chromosome to another nonhomologous chromosome, leading to abnormalities—e.g., Down syndrome. |
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Term
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Definition
| Having three of a particular type of chromosome (2n _ 1). |
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Term
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Definition
| Diploid cell formed by the union of two gametes; the product of fertilization. |
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