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34 Cards in this Set

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meiosis
Nuclear division that leads to a halving of the chromosome number.
chromatid
One of the daughter strands of a chromosome that has recently been copied (during mitosis or meiosis) and that is still connected to the other daughter strand.
centromere
The attachment structure joining two sister chromatids during mitosis and meiosis.
meiosis I
The first of two major cell-division events in meiosis, during which two genetically different haploid daughter cells are produced.
meiosis II
The second of two major cell-division events in meiosis, during which four genetically different haploid daughter cells are produced.
prophase I
The first stage of cell division in meiosis I, during which chromosomes begin to move to the middle of the cell.
homologous chromosomes (homologs)
Chromosomes of the same type, with the same genes in the same locations.
diploid
Having two sets of chromosomes. Diploid cells have two alleles of each gene--one on each of the homologous pairs of chromosomes.
tetrad
The structure that results from synapsis, consisting of two homologous chromosomes, each composed of two sister chromatids.
synapsis
The physical pairing of two homologs during prophase I of meiosis. Crossing over occurs during synapsis.
chiasma
The X-shaped structure formed during meiosis by crossing over between adjacent chromatids of a pair of homologous chromosomes.
metaphase I
The second stage of cell division in meiosis I, during which chromosomes line up in the middle of the cell.
anaphase I
The third stage of cell division in meiosis I, during which chromosomes move to opposite ends of the cell.
telophase I
The fourth and final stage of cell division in meiosis I, during which chromosomes finish moving and new nuclear envelopes begin to form around each set of daughter chromosomes.
haploid
Having a single set of chromosomes. Haploid cells have just one allele of each gene; they do not contain homologous chromosomes.
mitosis
Nuclear division in eukaryotes that produces two daughter nuclei that are genetically identical to the parent.
prophase II
The first stage of cell division in meiosis II, during which chromosomes begin to move to the middle of the cell.
metaphase II
The second stage of cell division in meiosis II, during which chromosomes line up in the middle of the cell.
diploid
Having two sets of chromosomes. Diploid cells have two alleles of each gene--one on each of the homologous pairs of chromosomes.
meiosis
Nuclear division that leads to a halving of the chromosome number.
haploid
Having a single set of chromosomes. Haploid cells have just one allele of each gene; they do not contain homologous chromosomes.
chromosome
A single long molecule of DNA and any associated proteins.
nondisjunction
An error that can occur during meiosis or mitosis in which both homologous chromosomes of a pair move to the same side of the dividing cell. One daughter cell receives two copies of this chromosome and the other daughter cell receives none.
homologous chromosomes (homologs)
Chromosomes of the same type, with the same genes in the same locations.
gamete
A haploid reproductive cell that can fuse with another haploid cell to form a zygote.
sister chromatids
The paired strands of a recently replicated chromosome that has not yet divided.
zygote
The diploid cell formed by the union of two haploid gametes. A zygote is capable of undergoing embryological development to form an adult organism.
trisomy
A condition in which a diploid cell or organism has an extra chromosome of one type, producing a chromosome number of 2n + 1.
Down syndrome
A chromosomal disorder resulting from trisomy of chromosome 21. The syndrome is characterized by mental retardation, a high risk for heart problems and leukemia, and a degenerative brain disorder similar to Alzheimerπs disease.
monosomy
A condition in which a diploid cell or organism lacks a chromosome of one type, producing a chromosome number of 2n ≠ 1.
Turner syndrome
A rare chromosomal disorder in females who have only one X chromosome. The syndrome is characterized by short stature, the lack of sexual development at puberty, and heart abnormalities.
triploid
Having three sets of chromosomes.
aneuploid
Having a chromosome number that is not an exact multiple of the normal diploid number, with either more or fewer than the normal number of chromosomes in the cell. Trisomy (having an extra chromosome) and monosomy (missing a chromosome) are examples.
polyploid
Having more than two sets of chromosomes. Triploidy, in which an organism has three complete sets of chromosomes, is an example.