Biology CH 9
Terms
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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.
- Histones?
- Chromosome packaging is facilitated by these proteins
- Nucleosomes?
- "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
- Mitosis?
- Division of the nucleus with its associated chromosomes
- Cytokinesis?
- Division of the cytoplasm.
- Interphase?
- 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.
- kinetochore?
- 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.
- MTOC?
- Microtubule organizing center. In animal cells-centrioles. where micrutubeles connect to chromosomes.
- Centrioles in interphase
- are duplicated to form 2 pairs.
- Asters?
- The microtubules that radiate from the centrioles.
- Aster movement
- Move towards opposite ends of the nucleus-> poles of mitotic spindle.
- Prophase?
- Aster movement. Nucleolus shrinks/disappears. Nuclear envelope breaks. Spindle forms.
- Metaphase
- 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.
- Anaphase
- Sister chromatids separate. Chromosomes move to opposite poles. Ends when all chromosomes have reached the poles.
- Telophase
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Chromosomes arrive at poles, return to interphase:
1- chromosomes condense
2- Nuclear envelope forms
3- nucleoli reorganize
4-Spindle microtubules disappear - Cytokinesis
- 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
- Meiosis
- 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.
- 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".
- 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.
- Interkinesis
- 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
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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?
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Mitosis-2n
Meiosid-n