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BIOL 1201 Study Guide - Midterm Guide: Spindle Apparatus, Homologous Chromosome, Sister Chromatids

Biological Sciences
Course Code
BIOL 1201
Study Guide

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Exam 4 Review
Cell cycle
o G1
o DNA synthesis (replication)
o G2
Chromosome structure
Eukaryotes chromosomes of eukaryotes are composed of DNA and histone proteins
that the DNA is wrapped on
o During interphase DNA is relaxed, extended
o During cell division DNA is condensed, supercoiled
o Chromosome can be un-replicated
1 molecule of DNA
o chromosome can be replicated
2 identical molecules of DNA held together
G1 chromosomes are un-replicated; they will stay that way throughout G1
S chromosomes replicate
G2 stay replicated through G2
Cell division go from replicated chromosomes to un-replicated chromosomes
Cell reproduction
Two steps
o Karyokinesis division of the nucleus
Mitosis, meiosis
o Cytokinesis division of the cytoplasm
Produces identical daughter cells (nuclei)
Identical to each other
Identical to parental cell (nucleus)
o Prophase
Nuclear envelope breaks down
Spindle apparatus forms
Chromosomes condense and are attached to the spindle
All chromosomes are replicated (four chromosomes, eight molecules of
o Metaphase
Chromosomes move to center of cell and are lined up on metaphase
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Four replicated chromosomes, eight molecules of DNA
o Anaphase
Replicated chromosomes separate (pulled apart)
Now each chromosome is un-replicated (eight un-replicated
chromosomes, eight molecules of DNA)
o Telophase
Chromosomes move to poles of each spindle; bunched on either side
(two groups)
Eight un-replicated chromosomes, eight molecules of DNA
o Cytokinesis
The poles divide into two cells
Division of the cytoplasm
Four un-replicated chromosomes and four molecules of DNA in each new
daughter cell
Daughter cells identical to each other and identical to parental cells
Roughly equal parts (generally)
Cleavage animal cells
Pinches the cell in two
Cell plate formation plant cell
Build cell plate from center moving out, deposit cell wall material
in the center, building until there are two parts
How many chromosomes are required to have one copy of each gene?
How many chromosomes are required to have one complete copy of all the DNA
needed to code for every protein in an organism
o Highly variable
Ploidy number of sets of chromosomes in a cell
o Haploid 1 set 1n
o Diploid 2 sets 2n
o Triploid 3 sets 3n
o Tetraploid 4 sets 4n
o Etc.
In one set of human chromosomes 23 chromosomes
o Haploid karyotype (1 chromosome for each set)
o Diploid karyotype (pair of chromosomes for each set
o Female a pair of X chromosomes for the 23rd pair
o Male an x and a y chromosome for the 23rd pair
Polyploid vs aneuploidy
o Polyploid more than two sets of chromosomes (triploid, tetraploid, hexaploid)
These individuals have extra copies for every gene that they have
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o Aneuploid change in the number of a single chromosome, not in the number of
sets do’s sdroe
Down’s syndrome the cells are diploid, but chromosome 21 has an
extra chromosome
24 chromosomes instead of the usual 23
problems including genetic machinery
homologous chromosomes
o same length
o same centromere
o same banding pattern
o all these chromosomes contain the same genes
produces non-identical daughter cells
not identical to each other or parental cell
each of the daughter cells have half the number of chromosomes of the original
parental cells
two important events
o segregation the homologous chromosomes separate into different daughter
o independent assortment the different pairs of chromosomes assort
independently from one another
process of meiosis
G1 un-replicated pair of chromosomes
S chromosomes replicate into a pair of replicated chromosomes
Meiosis I separate the homologous pair from one another (segregation)
into haploid cells with duplicated chromosomes
Meiosis II sister chromatids separate into two haploid cells with
unduplicated chromosomes
o Interphase
Chromosomes replicate
Centrosome duplicates
o Prophase I
Nuclear envelope breaks down
Spindle apparatus forms
Homologous chromosomes in synapsis touching each other but not in
the centromere region
Forms a tetrad formation four chromatids together in this pair of
replicated chromosomes
Chiasmata the place where they are touching each other
Crossing-over where one part of one chromosome switches
places with the same part of the other member of that pair
o Genetics
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