Biology Chapter 2: The Genetic Code - Cancer

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Genetic Code

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A string of mRNA nucleotides that translates the DNA nucleotide sequence into an amion acid sequence and ultimately into a protein.

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Degenerative

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An adjective describing the genetic code, explaining the fact that there is more than one series of three nucleotides that may code for a single amino acid.

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Unambiguous

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An adjective describing the genetic code, explaining that any single series of three nucleotides will code for one and only one amino acid.

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Almost Universal

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An adjective describing the genetic code, explaining that nearly every living organism uses the same code.

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AUG

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Start codon in the genetic code.

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UAA, UAG, UGA

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Stop codons in the genetic code; signal to end the synthesis of proteins.

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20

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Number of common amino acids.

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Codon

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Three consecutive nucleotides on a strand of mRNA.

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Translation

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The process of protein synthesis directed by mRNA.

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Anticodon

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A set of nucleotides complementary to the codon, carried by tRNA.

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Ribosome

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The site of translation; made up of rRNA and protein.

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Small and Large Subunits

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Comoponents of ribosomes (30S and 50S in prokaryotes, 40S and 60S in eukaryotes).

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Nucleolus

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A specialized organelle in eukaryotes where ribosomes are manufactured.

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Initiation

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The stage of translation when the tRNA possessing a complement to the start codon settles in at the P Site, signaling the large subunit to join and form the initiation complex.

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Elongation

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The stage of translation when tRNA attaches to the A site and the polypeptide begins to grow.

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Translocation

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An elongation step where the ribosome shifts three nucleotides along the mRNA toward the 3' end.

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E Site

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The location where the tRNA moves to exit the ribosome.

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Termination

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The end of translation, when a stop codon reaches the A site.

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Post-translational modifications

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A process where adjustments are made to a newly created protein (adding sugars, lipids, or phosphate groups, cleaving, joining other polypeptides, etc.)

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Signal Peptide

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A twenty amino acid sequence located near the front of a polypeptide that is recognized in order to move the polypeptide to the ER.

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Signal-Recognition Particle (SRP)

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A particle that carries an entire ribosome complex to the ER when it recognizes a signal peptide on the newly forming protein.

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Mutation

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Any alteration in the genome that is not genetic recombination.

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Gene Mutation

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The alteration of the sequence of DNA nucleotides of a single gene.

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Chromosomal Mutation

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The alteration of the structure of a chromosome.

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Mutagens

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Physical or chemical agents that induce mutations (increase the frequency of mutations about the frequency of spontaneous mutations).

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Point Mutation

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A type of mutation that changes a single base-pair of nucleotides in a double strand of DNA.

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Base-Pair Substitution Mutation

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A type of point mutation where one base-pair is replaced by another.

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Missense Mutation

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A type of point mutation that occurs in the amino acid coding sequence of a gene.

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Insertion

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A type of mutation where a base-pair is inserted into the nucleotide sequence.

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Deletion

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A type of mutation where a base-pair is removed from the nucleotide sequence.

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Frameshift Mutation

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A type of mutation resulting from a base-pair insertion or deletion (when the insertions or deletions occur in multiples other than 3).

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Nonsense Mutation

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A type of mutation when an insertion or deletiono creates a stop codon.

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Chromosomal Deletion

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A structural change to the chromosome when a part of it breaks off or is lost during homologous recombination and/or crossing over.

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Chromosomal Duplication

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A structural change to a chromosome when a fragment breaks free of one chromosome and is incorporated into a homologous chromosome.

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Reciprocal Translocation

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A type of chromosomal mutation when a segment of DNA on one chromosome is exchanged for a segment of DNA on another chromosome.

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Inversion

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A type of chromosomal mutation when the orientation of a section of DNA is reversed on a chromosome.

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Transposons/Transposable Elements

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DNA segments that can excise themselves from a chromosome and reinsert themselves at another location.

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Forward Mutation

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A term referring to a mutation in an already mutated organism that changes the organism even more from its original state.

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Backward Mutation

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A term referring to a mutation in an already mutated organism that changes the organism back to its original state.

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Wild Type

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The original state of an organism.

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Oncogens

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Genes that cause cancer.

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Carcinogens

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Mutagens that can cause cancer (eg: UV radiation, chemicals).

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Histones

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Globular proteins around which DNA wraps; eight of these from a nucleosome.

(Have a net positive charge due to their basicity.)

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Nucleosome

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Eight histones tightly wrapped in DNA.

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Chromatin

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The entire DNA/protein complex (histones, nucleosomes, etc.).

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Chromosomes

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46 double-stranded DNA molecules found within the nucleus of a human somatic cell.

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Homologous Chromosomes/Homologues

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Two chromosomes that code for the same traits. Humans possess 23 pairs of these.

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Diploid

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An adjective describing any cell that contains homologous pairs of chromosomes.

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Haploid

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An adjective describing any cell that does not contain homologues.

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Interphase

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The collective name for G1, S, and G2 stages of a cell's life cycle.

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The First Growth Phase (G1)

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The stage of a cell's life cycle where the cell has just split, is growing, producing organelles and proteins, and is undergoing active transcription and translation.

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G1 Checkpoint

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A point during the cell life cycle when the cell growth is assessed to see whether or not it is prepared for division.

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G0 Phase

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A nongrowing state in a cell's life cycle distinct from interphase. This phase allows for differences in the length of a cell cycle depending on a cell's function in the body.

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S Phase (Synthesis)

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The stage in a cell's life cycle that occurs after the first growth phase. The cell devotes most of its energy to replicating DNA.

Chromosomes --> Sister Chromatids

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Chromatids

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Two identical sisters of the original chromosome, produced during S Phase of a cell's life cycle.

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G2 (Second Growth Phase)

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The phase that occurs after synthesis of chromatids in a cell's life cycle.

The cell is preparing to divide with active synthesis of proteins (esp. microtubules) and RNA.

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G2 Checkpoint

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A point during the second growth phase where the level of mitosis promoting factor (MTF) is assessed.

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M Checkpoint

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A point during mitosis that triggers the start of the first growth phase.

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Mitosis

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Nuclear division without genetic change.

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Prophase

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The first step in mitosis, characterized by the condensation of chromatin into chromosomes.

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Metaphase

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The second step in mitosis, where chromosomes align along the equator of the cell.

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Anaphase

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The third step of mitosis where sister chromatids split at their attaching centromers and move toward opposite ends of the cell (disjunction).

Cytokinesis begins at the end of this phase.

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Cytokinesis

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A term for the separation of cellular cytoplasm during the end of anaphase and beginning of telophase in mitosis.

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Telophase

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The fourth and final step of mitosis during which the nuclear membrane and nucleolus reforms. Chromosomes decondense. Cytokinesis continues.

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Centrosomes

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An organelle that serves as the main microtubule organizer of the cell.

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Centrioles

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A cylindrical cell structure composed of tubulin, located within a centrosome.

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Spindle Apparatus & Microtubules

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A cell structure that segregates chromosomes between daughter cells during cell division.

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Aster

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A star-shaped cellular structure formed around each centrosome during mitosis.

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Kinetochore

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A structure of protein and DNA located at the centromere of the joined chromatids of each chromosome.

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Centromeres

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The part of the chromosome that links sister chromatids.

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Meiosis

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A double nuclear division that produces four haploid gametes (germ cells).

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Spermatogonium

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An undifferentiated germ cell that gives rise to sperm cells. One of the only two cells that undergoes meiosis in humans.

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Oogonium

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An undifferentiated germ cell that gives rise to oocytes. One of the only two cells that undergoes meiosis in humans.

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Primary Oocyte

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A germ cell in females that has undergone replication during S phase, waiting to undergo the first round of meiosis.

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Primary Spermatocyte

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A germ cell in males that has undergone replication during S phase, waiting to undergo the first round of meiosis.

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Prophase I

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The first stage of Meosis I. Homologous chromosomes match up their DNA. Crossing over occurs during this stage.

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Prophase II

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The first stage of Meiosis II/last stage of Meiosis I.

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Metaphase I

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The second stage of the Meiosis I. Tetrads align during this stage.

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Metaphase II

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The second stage of Meiosis II.

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Anaphase I

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The third stage of Meiosis I. Homologous chromosome are separated from their partners.

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Anaphase II

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The third stage of Meiosis II.

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Telophase I

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The fourth stage of Meiosis I.

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Telophase II

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The final stage of Meiosis II, before the gametes enter interphase.

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Crossing Over

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The process by which homologous chromoosome exchange sequences of DNA. Occurs during Prophase I of meiosis. Genetic recombination occurs due to this process.

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Tetrads

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A name for the four chromatids lined up in Prophase I of Meiosis I.

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Chiasma

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A name for the x-shape that is seen under the microscope when looking at a pair of chromosomes during Prophase I of meiosis.

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Nondisjunction

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When the centromere of a chromosome does not split during anaphase I or II in meiosis.

(Down Syndrome, chromosome 21)

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Secondary Spermatocytes or Oocytes

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The name for cells produced in humans through meiosis I.

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Polar Body

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One of the oocytes in the female that is smaller and degenerates following Meiosis I (and potentially meiosis II...)