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somatic cells

cells of the body, other than those of the ovaries and testes

sex cells

gametes; egg and sperm


division of the nucleus


division of the cytoplasm


programmed cell death


phase of cell cycle composed of G1, S and G2

growth factors

hormones that act as external signals binding at the plasma membrane


protein molecules which act as internal signals for the phases of the cell cycle

p53 protein

a protein coded for by the p53 gene that stops the cell cycle at the G1 checkpoint if DNA is damaged

p53 gene

a gene on a chromosome which codes for the p53 protein


enzymes that cause apoptosis


DNA in a non-dividing cell which takes the form of long threads not visible under a light microscope


DNA which condenses into distinct structures seen during mitosis and meiosis

S phase

phase of interphase during which DNA replication takes place

G1 phase

phase of interphase during which doubling of organelles takes place

G2 phase

phase of interphase; synthesis of proteins needed for cell division occurs.


2n; the total number of chromosomes in somatic cells


n; the number of chromosomes in an egg or sperm


phase of mitosis; nuclear envelope disappears, chromosomes become visible, spindle fibers form


phase of mitosis; chromosomes line along equator of cell


phase of mitosis; centromeres replicate, sister chromosomes move into opposite poles of cell


phase of mitosis; nuclear envelope reassembles, cytokinesis begins

cleavage furrow

pinching of animal cells that occurs during cytokinesis

cell plate

forms in plant cells during cytokinesis


cell division in which the chromosome number is reduced by half

duplicated chromosome

chromosome which has two sister chromatids joined by a centromere


a structure which joins two sister chromatids


the pairing of homologous chromosomes that occurs during prophase I

reduction division

meiosis I (chromosoe number goes from diploid to haploid)


joining of egg and sperm; forms the zygote


the diploid cell that results from the fusion of egg and sperm at fertilization

crossing over

the exchange of genetic information which occurs during synapsis, during prophase I

independent assortment

the random movement of maternal and paternal chromosomes along the metaphase plate during Metaphase I; causes genetic variability


the period of time between meiosis I and II


the failure of homologous chromosomes to separate during Anaphase I or failure of sister chromatids to separate in Anaphase II

Down syndrome

trisomy 21; a result of nondisjunction

Turner's syndrome

a female with only one X chromosome; caused by nondisjunction. Egg of mother or sperm of father was missing an X Chromosome


meiosis in males


meiosis in females

primary spermatocyte

a diploid cell; divides during Meiosis I into 2 secondary spermatocytes

secondary spermatocyte

a haploid cell; divides during meiosis II forming spermatids


mature sperm cells

primary oocyte

a diploid cell; divides during meiosis I into a secondary oocyte and the first polar body

secondary oocyte

haploid cell; divides during meiosis II into an ovum and another polar body


mature eff produced by female

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