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50 Cards in this Set

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What are chromosomes?
Major carriers of genetic information
What are chromosomes made up of?
Chromatin-consists of Dna & proteins
Describe chromosomes & chromatin when a cell is not dividing.
Extended partially unraveled form. Long thin threads, granular appearence.
Chromosome packaging is facilitated by these proteins
"beads on a string" 8 histone molecules wrapped with DNA.
What is a karyotype?
chromosomal constitution of an individual
What does the cell cycle consist of?
M phase & interphase
M Phase?
Mitosis & Cytokinesis
Division of the nucleus with its associated chromosomes
Division of the cytoplasm.
Stage of growth between succesive cell divisions
Interphases' 3 stages?
S, G1, G2
S phase?
Dna is replicated. DNA systhesis occurs.
G1 phase?
When cell is making preparations for DNA sythesis. Precedes S phase.
G2 phase
Follwing the S phase. Cell makes preparations to divide.
Sister chromatids?
identical, double-stranded DNA sequences.
Formed from proteins, to which microtubules can bind.
Mitotic spindle?
When microtubules radiate from each pole, these fibers elongate towards chromosomes. Seperates chromosomes during anaphase.
Microtubule organizing center. In animal cells-centrioles. where micrutubeles connect to chromosomes.
Centrioles in interphase
are duplicated to form 2 pairs.
The microtubules that radiate from the centrioles.
Aster movement
Move towards opposite ends of the nucleus-> poles of mitotic spindle.
Aster movement. Nucleolus shrinks/disappears. Nuclear envelope breaks. Spindle forms.
Cell's chromosomes align at the cell's midplane (METAPHASE PLATE)
Mitotic spindles: Microtubules
Polar and Kinetochore
Polar Microtubules
extend from each pole to the equilateral region, where they overlap.
Kinetochore Microtubles
extend from each pole and attatch to kinetochores.
Sister chromatids separate. Chromosomes move to opposite poles. Ends when all chromosomes have reached the poles.
Chromosomes arrive at poles, return to interphase:
1- chromosomes condense
2- Nuclear envelope forms
3- nucleoli reorganize
4-Spindle microtubules disappear
Division of the cytoplasm to yield 2 daughter cells, overlaps mitosis, beginning during telophase.
Cytokinesis: animal
Ring of actin microfilaments encircle the cell in the equilateral region. The ring contracts producing a CLEAVAGE FURROW, that seperates the cytoplasm into to 2 daughter cells. outside->inward
Cytokinesis: plant
Forming a cell plate, partition constructed in the equilateral region of the spindle and growing laterally toward the cell wall. center->outward
Asexual reproduction
Single parent splits, buds, fragments to produce 2 or more individuals. All cells are result of mitotic divisions.
Sexual reproduction
2 sex cells (gametes) form a zygote. Results in genetic variation. (genetically different from parents).
Homologous chromosomes
Similiar in size, shape, and position of their centromeres
"Set" of chromosomes
One of each kind of chromosome. 1 member of each homologous pair. 2 sets-dipoloid. 1 set- haploid. 3 or more-polyploid
chromosome number n
Haploid chromosome # is n. Diploid is 2n. Humans: n=23
Division that reduces the chromosome number by half. A diploid cell undergoes 2 cell divisions potentially yielding 4 haploid cells.
Prophase I
Homologous chromosome pairs synapse to make tetrads (4 chromatids).
Synaptonemal complex
structure that holds homologous chromosomes together when they synapse. Plays role in crossing over.
Paired homologous chromosomes exchange genetic material (DNA). Produces new combinations of genes.
Prophase & Prophase I
Similar-xcept- the homologous chromosomes are held by "Chiasmata".
Site at which homologous chromatids exchange genetic material.
Metaphase I
Tetrads line up on cell's midplane
Anaphase I
Homologous chromosomes seperate and move to opposite poles.
Telophase I
Chromatids recondense, nuclear envelope may reorganize, cytokinesis may take place. Each nucleus contains the haploid number of chromosomes.
Stage following Telophase I, that has interphse like stages without the S-phase.
Telophase II
Nuclear envelopes reform, chromosomes elongate to form chromatin fibers, cytokinesis occurs.
Sources of genetic variation
1- maternal and paternal chromosomes of homologous pairs seperate independently. The chromosomes are shuffled.
2- DNA segments are exchanged between maternal and paternal homologues during cross over.
Parent cell is 2n, what is the chromosome number of daughter cells?