Mitosis and Meiosis Flashcards
contain their genetic information
in pairs of homologous chromosomes, with one
member of each pair being derived from the maternal
parent and one from the paternal parent.
diploid eukaryotic cells
s provides a mechanism by which chromosomes,
having been duplicated, are distributed into progeny
cells during cell reproduction.
mitosis
converts a diploid cell into two diploid daughter
cells.
mitosis
The process of ___distributes one member of each
homologous pair of chromosomes into each gamete or
spore, thus reducing the diploid chromosome number
to the haploid chromosome number.
meiosis
generates genetic variability by distributing
various combinations of maternal and paternal members
of each homologous pair of chromosomes into gametes
or spores
meiosis
During the stages of mitosis and meiosis, the genetic
material is condensed into discrete structures called
chromosomes
DNA has an
underlying linear structure possessing segments called
genes
An organism’s DNA, with its arrays of genes, is organized into
structures called
chromosomes
vehicles
for transmitting genetic information.
chromosomes
Two major processes are involved in the genetic continuity of nucleated cells
mitosis
meiosis
leads to the production of two cells, each with the same number of chromosomes
as the parent cell. I
mitosis
reduces the genetic content and the number of chromosomes by precisely half.
meiosis
This
reduction is essential if sexual reproduction is to occur without
doubling the amount of genetic material in each new generation
meiosis
is that portion of the cell cycle
during which the hereditary components are equally partitioned into daughter cells.
mitosis
is part of a special type of
cell division that leads to the production of sex cells
meiosis
Meiosis is part of a special type of
cell division that leads to the production of sex cells
gametes
spores
Normally, chromosomes are visible only
mitosi and meiosis
When cells are not undergoing division, the
genetic material making up chromosomes unfolds and uncoils
into a diffuse network within the nucleus, generally referred to
as
chromatin
Under the ___ microscope, cells were seen
as highly varied, highly organized structures whose form
and function are dependent on specific genetic expression by
each cell type
electron
organelles that contain their own unique genetic information.
chloroplast
mitochondria
All cells are surrounded by a
plasma membrane
an
outer covering that defines the cell boundary and delimits the cell from its immediate external environment
plasma membrane
In addition to this membrane, plant cells have an outer
covering called the
cell wall
cell wall whose major component is a
polysaccharide called
cellulose
Many, if not most, animal cells have a covering over the
plasma membrane, referred to as the
glycocalyx
glycocalyx is also known as
cell coat
Consisting of glycoproteins and polysaccharides, this
covering has a chemical composition that differs from comparable structures in either plants or bacteria.
glycocalyx
provides biochemical identity at the
surface of cells, and the components of the coat that establish
cellular identity are under genetic control. F
glycocalyx
are also found on the surfaces of cells.
These molecules act as recognition sites that transfer specific
chemical signals across the cell membrane into the cell.
receptor molecules
The presence of a nucleus and other membranous
organelles is the defining characteristic of
eukaryotic organisms
in eukaryotic cells is a membranebound structure that houses the genetic material, DNA,
which is complexed with an array of acidic and basic proteins into thin fibers.
nucleus
During nondivisional phases of the cell
cycle, the fibers are
uncoiled and dispersed into chromatin
During mitosis and meiosis, chromatin fibers coil and condense into
chromosomes
an amorphous component
where ribosomal RNA (rRNA) is synthesized and where the
initial stages of ribosomal assembly occur
nucleolus
The portions of
DNA that encode rRNA are collectively referred to as the
nucleolus organizer region (NOR)
of which there are two major
groups, lack a nuclear envelope and membranous organelles.
prokaryotic organisms
In eubacteria, such
as Escherichia coli, the genetic material is present as a
long circular DNA molecule
In eubacteria, such
as Escherichia coli, the genetic material is present as a long,
circular DNA molecule that is compacted into an unenclosed region called the
nucleoid
do not have a
distinct nucleolus but do contain genes that specify rRNA
molecules.
prokaryotic cells
The remainder of the eukaryotic cell within the plasma
membrane, excluding the nucleus, is referred to as
cytoplasm
In
the cytoplasm, a nonparticulate, colloidal material referred
to as the ___ surrounds and encompasses the cellular
organelles.
cytosol
he cytoplasm also includes an extensive system
of tubules and filaments, comprising the
cytoskeleton
which
provides a lattice of support structures within the cell.
cytoskeleton
cytoskeleton is comprised mainly of
microtubules
microtubules are made of the protein
tubulin
microfilaments
microfilaments are derived from what protein
actin
compartmentalizes the cytoplasm, greatly
increasing the surface area available for biochemical synthesis.
endoplasmic reticulum
The ER appears smooth in places where it serves as the
site for
synthesizing fatty acid and phospholipids
appears rough because it is studded with ribosomes
RER
s serve as sites where genetic information contained in messenger RNA (mRNA) is translated into proteins.
ribosomes
are found in
most eukaryotes, including both animal and plant cells,
and are the sites of the oxidative phases of cell respiration. These chemical reactions generate large amounts of
the energy-rich molecule adenosine triphosphate (ATP).
mitochondria
which are found in plants, algae, and some
protozoans, are associated with photosynthesis, the major
energy-trapping process on Earth
chloroplast
Animal cells and some plant cells also contain a pair
of complex structures called
centrioles
These cytoplasmic bodies, each located in a specialized region called
the
centrosome
are associated with the organization
of spindle fibers that function in mitosis and meiosis.
centrosome
In some organisms, the centriole is derived from another
structure
basal body
In some organisms, the centriole is derived from another
structure, the basal body, which is associated with the formation of
cilia and flagella
hair-liek structures
cilia
whip-like structures
flagella
The organization of ___ ___by the centrioles
occurs during the early phases of mitosis and meiosis.
spindle fibers
are most
easily visualized during mitosis.
chromosomes
Each chromosome contains a constricted region called the
centromere
whose location establishes the general appearance of
each chromosome
centromere
The shorter arm,
by convention, is shown above the
centromere and is called the
p arm
longer arm
q arm
First, all ___cells derived
from members of the same species contain an identical
number of chromosomes.
somatic
With the exception of sex chromosomes, they exist in
pairs with regard to these two properties, and the members of each pair are called
homologous chromosomes
So, for each chromosome exhibiting a specific length and
centromere placement, another exists with identical
features.
what are exceptions?
bacteria and viruses (1 chromosome)
yeasts and molds
bryophytes
plants that spend their predominant phase of their life cycle in
the haploid stage
bryophytes
centromere location in the middle
metacentric
centromere location between middle and end
submetacentric
centromere location close to end
acrocentric
centromere location at end
telocentric
There, the
human mitotic chromosomes have been photographed, cut
out of the print, and matched up, creating a display called a
karyotype
Note also that each
of the 46 chromosomes in this karyotype is clearly a double
structure consisting of t
two parallel sister chromatids
is equal to
one-half the diploid number. C
haploid
r. Collectively, the genetic information contained in a haploid set of chromosomes constitutes the
genome
Homologous chromosomes have important genetic
similarities. They contain identical gene sites along their
lengths; each site is called a l
locus
). Therefore, each diploid
organism contains two copies of each gene as a consequence
of
biparental inheritance
inheritance from two parents.
biparental inheritance
. In a population of members of the same species,
many different alternative forms of the same gene, called
allele
s. During the formation of gametes or
spores, meiosis converts the ___number of chromosomes
to the ___number
diploid
haploid
As a result, haploid gametes or spores
contain precisely ___ member of each homologous pair of
chromosomes—that is, one complete haploid set.
one
. Following
fusion of two ___at fertilization, the diploid number is
reestablished; that is, the zygote contains two complete haploid sets of chromosomes.
gametes
In many species, one pair,
consisting of the ___-____ chromosomes, is often
not homologous in size, centromere placement, arm ratio,
or genetic content.
sex determining chromosomes
is considerably smaller and lacks most of the gene loci
contained
what sex chromosome
Y
organisms that have mitosis as basis for asexual reproduction
fungi
algae
protozoans
Multicellular diploid organisms begin life as single-celled fertilized eggs called
zygotes
The ___ activity of the zygote and the subsequent daughter cells is the foundation for the development
and growth of the organism
mitotic
In adult organisms, mitotic
activity is the basis for
wound healing
cell replacement in tissues
eventually
shed their nuclei and replenish the supply of red blood cells
in vertebrates
reticulocytes
In abnormal situations, somatic cells may lose
control of cell division, and form a
tumor
The genetic material is partitioned into daughter cells
during nuclear division, or
karyokinesis
Karyokinesis is followed by cytoplasmic division called
cytokinesis
nondividing phase
G0
requires a mechanism that partitions the volume into two parts and
then encloses each new cell in a distinct plasma membrane.
cytokinesis
Following cell division, the initial size of each new
daughter cell is approximately what size of the
parent cell
one-half
does the nucleus of the new cell be half in size with the old nucleus
no
The events that occur from the completion of
one division until the completion of the next division constitute the
cell cycle
the initial stage of the cell cycle, as the interval between divisions
interphase
interphase also is a biochemical step critical to the ensuing mitosis because it
replicates DNA of each chromosome
This
period, during which DNA is synthesized, occurs before the
cell enters mitosis and is called the
s phase
The initiation
and completion of synthesis can be detected by monitoring the
incorporation of radioactive precursors into DNA
how long is G1
5 hours
how long is S phase
7 hours
how long is G2
3 hours
how long is M
1 hour
how long is prophase
36 minutes
how long is metaphase
3 minutes
how long is anaphase
3 minutes
how long is telophase
18 minutes
By
the end of __ , the volume of the cell has roughly doubled,
S phase
When grown in culture, many cell
types in different organisms traverse the complete cycle in
about __ hours
16 hours
Most variation is seen in
the length of time spent in the
G1 stage
stage of mitosis that is of great interest in the study of cell proliferation
and its control.
G1
At a point during G1, all cells follow one of
two paths
(1) withdraw from the cycle and become quiescent and enter G0 stage
(2) committed to proceed through G1, initiating DNA synthesis and completing the cycle
Cells that enter ___
remain viable and metabolically active but are not proliferative.
G0
cells that apparently avoid entering G0 or pass
through it very quickly.
cancer cells
is characterized by the absence
of visible chromosomes.
interphase
Cytologically, interphase is characterized by the absence
of visible chromosomes. Instead, the nucleus is filled with
chromatin fibers
s is a
dynamic period of vigorous and continual activity
mitosis
Often, over half of mitosis is spent in
prophase
One of the early events in prophase of all animal cells is the
migration of two pairs of centrioles to the opposite ends of the cell
These structures are found just outside the nuclear envelope in an area of differentiated cytoplasm called the centrosome
centrioles
area of differentiated cytoplasm outside the nuclear envelop
centrosome
It
is believed that each pair of centrioles consists
one mature unit
smaller newly formed daughter centriole
The centrioles migrate and establish __at opposite
ends of the cell
poles
After migration, the centrosomes, in which
the ___ are localized, are responsible for organizing
cytoplasmic microtubules into the spindle fibers
centrioles
After migration, the centrosomes, in which
the centrioles are localized, are responsible for organizing
___ ____ into the spindle fiber
cytoplasmic microtubules
After migration, the centrosomes, in which
the centrioles are localized, are responsible for organizing
cytoplasmic microtubules into the ___ ___
spindle fiber
Interestingly, the cells of most
plants (there are a few exceptions), fungi, and certain algae
seem to lack ___
centrioles
As the centrioles migrate, the ___ ___begins to
break down and gradually disappears
nuclear envelope
In a similar fashion,
the ___ disintegrates within the nucleus.
nucleolus
While these
events are taking place, the diffuse chromatin fibers have
begun to condense, until distinct thread-like structures, the
___, become visible
chromosome
. It becomes apparent near the
end of prophase that each chromosome is actually a double
structure split longitudinally except at a single point of constriction called the
centromere
The two parts of each chromosome
are called
sister chromatids
Sister chromatids are held together
by a multi-subunit protein complex called
cohesin
This
molecular complex is originally formed between them during the S phase of the cell cycle when the DNA of each chromosome is replicated
cohesin
cohesin is originally formed between them during the ___ phase of the cell cycle when the DNA of each chromosome is replicated
S
Thus, even though we cannot see
chromatids in interphase because the chromatin is uncoiled
and dispersed in the nucleus, the chromosomes are already
double structures, which becomes apparent in what stage
late prophase
In humans, with a diploid number of __, a cytological preparation of late prophase reveals 46 chromosomes randomly
distributed in the area formerly occupied by the nucleus.
46
The distinguishing event of the two ensuing stages is the
migration of every chromosome, led by its centromeric region,
to the equatorial plane
prometaphase and metaphase
, is the midline region of the cell, a plane
that lies perpendicular to the axis established by the spindle
fibers
equatorial plane (metaphase plate)
refers
to the period of chromosome movement
prometaphase
is applied strictly to the chromosome
configuration following migration
metaphase
Migration is made possible by the binding of spindle
fibers to the chromosome’s
kinetochore
an assembly of
multilayered plates of proteins associated with the centromere.
kinetochore
This structure forms on opposite sides of each paired
centromere, in intimate association with the two sister chromatids
kinetochore
Chromosomes are
extended and uncoiled,
forming chromatin
what stage
interphase
Chromosomes coil up
and condense; centrioles
divide and move apart
what stage
prophase
Chromosomes are clearly
double structures; centrioles
reach the opposite poles;
spindle fibers form
what phase
prometaphase
Centromeres align
on metaphase plate
what phase
metaphase
Centromeres split and daughter
chromosomes migrate to opposite poles
what phase
anaphase
Daughter chromosomes arrive at
the poles; cytokinesis commences
what phase
telophase
Once properly attached to the spindle fibers,
cohesin is degraded by an enzyme, appropriately named
separase
Once properly attached to the spindle fibers,
cohesin is degraded by an enzyme, appropriately named
separase, and the sister chromatid arms disjoin, except
at the
centromere region
A unique protein family called ___ protects cohesin from being degraded by separase at the
centromeric regions
shugoshin
shugoshin means
guardian spirit
Altered kinetechore function potentially leads to errors during
chromosome migration
consist of microtubules, which themselves consist of molecular subunits of the protein tubulin
spindle fibers
Spindle fibers consist of ___, which themselves consist of molecular subunits of the protein tubulin
microtubule
Spindle fibers consist of microtubules, which themselves consist of molecular subunits of the protein ___
tubulin
Microtubules seem to originate and “grow” out of the two
___regions at opposite poles of the cell
centrosome
They are
dynamic structures that lengthen and shorten as a result of
the addition or loss of polarized tubulin subunits
spindle fibers
most directly responsible for chromosome migration make contact with, and adhere to, kinetochores as they
grow from the centrosome region are referred to as
kinetochore microtubules
have one end near the centrosome region (at one of the poles of the cell) and the other
end anchored to the kinetochore.
kinetochore microtubule
has only a single microtubule bound to each plate-like structure of the kinetochore.
yeast (saccharomyces cerevisiae)
Mitotic cells of mammals, at the other extreme, reveal __ to
__ microtubules bound to each portion of the kinetochore
30 to 40
At the completion of ___, each centromere is
aligned at the metaphase plate with the chromosome arms
extending outward in a random array
metaphase
Events critical to chromosome distribution during mitosis
occur during ____, the shortest stage of mitosis
anaphase
During this phase, sister chromatids of each chromosome, held
together only at their centromere regions, disjoin (separate)
from one another
anaphase
During this phase, sister chromatids of each chromosome, held
together only at their centromere regions, disjoin (separate)
from one another—an event described as
disjunction
for complete disjunction to occur in anaphase, 3 conditions must happen
(1) shugoshin must be degraded
(2) cohesin complex holding the centromere region at each sister chromosome is cleaved by separate
(3) sister chromatids of each chromosome are pulled towards the opposite poles of the ecell
As these events proceed, each migrating chromatid is now
referred to as a
daughter chromosome
Movement of daughter chromosomes to the opposite
poles of the cell is dependent on the
kinetochore-spindle fiber attachment
Recent investigations reveal that chromosome migration results from the activity of a series
of specific molecules called
motor proteins
found at several locations within the dividing cell that enables chromosome migration
motor proteins
proteins that use the energy generated by the hydrolysis of ATP
molecular motors
Their effect on the activity
of microtubules serves ultimately to shorten the spindle
fibers, drawing the chromosomes to opposite ends of the
cell
molecular motors
The ___of each chromosome appear to lead
the way during migration, with the chromosome arms
trailing behind.
centromeres
The location of the centromere determines the ____
of the chromosome during separation
shape
In human cells, there would now be ___
chromosomes at each pole, one from each original sister
pair after anaphase
46
is the final stage of mitosis
mitosis
the division or partitioning of the cytoplasm.
cytokinesis
in plant cells, cytokinesis creates a ___ laid down across
the region of the metaphase plate
cell plate
what happens in cytokinesis if animal cell
constriction of cytoplasm
Plant cells, which are more regularly shaped and structurally rigid, require a mechanism
for depositing new cell wall material around the plasma
membrane. The cell plate laid down during telophase
becomes a structure called the
middle lamella
In animals,
complete constriction of the cell membrane produces the
cell furrow
Other events necessary for the transition from mitosis to interphase are initiated during
late telophase
They
generally constitute a reversal of events that occurred during prophase.
late telophase
At
the completion of telophase, the cell enters
interphase
A mammoth research effort over the past 20 years has
paid high dividends, and we now have knowledge of many
genes involved in the control of the cell cycle. This work was
recognized by the awarding of the 2001 Nobel Prize in Medicine or Physiology to (3)
Lee Hartwell
Paul Nurse
Tim Hunt
. First discovered in
yeast, but now evident in all organisms, including humans,
such mutations were originally designated as
cell division cycle (CDC) mutations
what organisms were first discovered to have CDC mutations
yeast
The normal products of many of
the mutated genes are enzymes called
kinases
that can
add phosphates to other proteins
kinases
They serve as “master control” molecules functioning in conjunction with proteins
called cyclins
kinases
bind to these kinases (creating cyclindependent kinases), activating them at appropriate times
during the cell cycle.
cyclin
cyclin binding to kinases creates
cyclin dependent kinases
Activated kinases then undergo what process
other target proteins that regulate the progress of the cell
cycle.
phosphorylate
The study of cdc mutations has established that the
cell cycle contains at least three
cell cycle checkpoint
where the processes culminating in normal mitosis are
monitored, or “checked,” by these master control molecules
before the next stage of the cycle is allowed to commence
cell cycle checkpoint
If allowed to proceed
through the cell cycle, this genetically altered cell would divide
uncontrollably—a key step in the development of a
cancer cell
If an organism has a diploid number of 16, how many
chromatids are visible at the end of mitotic prophase?
32 chromatids
How many chromosomes are moving to each pole
during anaphase of mitosis?
16 chromosomes
produces
gametes or spores that are characterized by only one haploid
set of chromosomes
meiosis
During sexual reproduction, haploid
gametes then combine at ___to reconstitute theiploid complement found in parental cells
fertilization
must be highly specific since, by definition, haploid gametes or spores must contain precisely one
member of each homologous pair of chromosomes
meiosis
Another major accomplishment of meiosis is to ensure
that during sexual reproduction an enormous amount of
___ ___is produced among members of a species.
genetic variation
The second source of variation is created by the
meiotic event referred to as
crossing over
which results in
genetic exchange between members of each homologous pair
of chromosomes prior to one or the other finding its way into
a haploid gamete or spore
crossing over
he meiotic achievements, as
described above, are largely dependent on the behavior of
chromosomes during the initial stage of the first division,
called
prophase I
Each
chromosome is duplicated, creating genetically identical sister chromatids, and subsequently, one chromatid of each pair
is distributed to each new cell
prophase I
The major difference in meiosis
is that once the chromatin characterizing interphase has condensed into visible structures, the homologous chromosomes
are not autonomous but are instead seen to be paired up, having undergone the process called
synapsis
Each synapsed pair of homologs is initially called a
bivalent
and the number of bivalents is equal to the ___ number
haploid
r. In
Figure 2.10, we have depicted two homologous pairs of chromosomes and thus two bivalents. As the homologs condense
and shorten, each bivalent gives rise to a unit called a
tetrad
consisting of two pairs of sister chromatids, each of which is joined at a common centromere
tetrad
An organism has a diploid number of 16 in a primary
oocyte.
(a) How many tetrads are present in the first
meiotic prophase?
8 tetrads
An organism has a diploid number of 16 in a primary
oocyte.
(b) How many dyads are present in the
second meiotic prophase?
8 dyads
An organism has a diploid number of 16 in a primary
oocyte.
(c) How many monads migrate
to each pole during the second meiotic anaphase?
8 monads
However, one or more areas remain in contact where chromatids are intertwined. Each such area, called
a
chiasma
, is thought to represent a point
where nonsister chromatids (one paternal and one maternal chromatid) have undergone genetic exchange through
the process of crossing over
chiasma
first division after prophase I, the chromosomes have maximally shortened and thickened.
metaphase I
f each tetrad are visible and
appear to be the major factor holding the nonsister chromatids together
terminal chiasmata
During the stages of ___ , a single centromeric
region holds each pair of sister chromatids together.
meiosis I
At anaphase I, ___is degraded between sister chromatids, except at the centromere region, which, as in mitosis,
is protected by a shugoshin complex
cohesin
At ___, cohesin is degraded between sister chromatids, except at the centromere region, which, as in mitosis,
is protected by a shugoshin complex
anaphase I
Then, one-half of eachtetrad (a dyad) is pulled toward each pole of the dividing
cell.
what phase
anaphase I
Because this process effectively reduces the number
of centromeres by half, it is referred to as a
reductional division
r. Occasionally, errors in meiosis occur and separation
is not achieved. The term ___describes such an
error
non disjunction
At the completion of the normal___, a series of
dyads equal to the haploid number is present at each pole
anaphase I
At the completion of the normal anaphase I, a series of
dyads equal to the ___number is present at each pole
haploid
In many organisms, ___ I reveals a nuclear membrane forming around the dyads. In this case, the nucleus next enters into a short interphase period
telophase I
If ___ occurs, the
chromosomes do not replicate because they already consist of
two chromatids
interphase
In other organisms, the cells go directly from
anaphase I to meiosis II
. In general, meiotic ___is much
shorter than the corresponding stage in mitosis.
telophase
is essential if each
gamete or spore is to receive only one chromatid from each
original tetrad
meiosis II
each
dyad is composed of one pair of sister chromatids attached
by the common centromeric region.
prophase
the centromeres are positioned on the equatorial plate. When
the shugoshin complex is degraded, the centromeres separate
what stage in meiosis II
metaphase II
I is initiated, and the sister chromatids of
each dyad are pulled to opposite poles. Because the number
of dyads is equal to the haploid number
anaphase II
reveals
one member of each pair of homologous chromosomes present at each pole
telophase II
Each chromosome is now a ___ at telophase II
monad
Because
the number of centromeres is not reduced in number in the
two resulting cells, the process is referred to as an
equational division
Following cytokinesis in telophase II, ___haploid gametes may result from a single meiotic event
four
production of a male gamete
spermatogenesis
production of female
gamete
oogenesis
___takes place in the testes, the male
reproductive organs. T
spermatogenesis
Spermatogenesis takes place in the ___, the male
reproductive organs.
testes
The process begins with the enlargement of an undifferentiated diploid germ cell called a
spermatogonium
The process begins with the enlargement of an undifferentiated diploid germ cell called a
spermatogonium. This cell grows to become a
primary spermatocyte
which undergoes the first meiotic division in spermatogenesis
primary spermatocyte
This cell grows to become a primary
spermatocyte, which undergoes the first meiotic division. The products of this division, called
secondary spermatocytes
contain a haploid number of dyads
secondary spermatocytes
The
secondary spermatocytes then undergo ____, and
each of these cells produces two haploid spermatids
meiosis II
The
secondary spermatocytes then undergo meiosis II, and
each of these cells produces two haploid ___
spermatids
Spermatids go through a series of developmental changes called
spermiogenesis
Spermatids go through a series of developmental changes,
spermiogenesis, to become highly specialized, motile
spermatozoa or sperm
All sperm cells produced during
spermatogenesis contain the ____ number of chromosomes and ___ amounts of cytoplasm
haploid
equal
s may be continuous or may occur periodically in mature male animals;
spermatogenesis
the formation of ova (sing.
ovum), or eggs, occurs in the ovaries, the female reproductive organs. T
oogenesis
In animal oogenesis, the formation of ova (sing.
ovum), or eggs, occurs in the
ovaries
The daughter cells resulting from the two
meiotic divisions of this process receive equal amounts of
___ ___, but they do not receive equal amounts
of ____
genetic material
cytoplasm
Instead, during each division, almost all the
cytoplasm of the primary ___, itself derived from the
oogonium
oocyte
why is the concentration of cytoplasm needed in oogenesis
The concentration of cytoplasm is necessary because
a major function of the mature ovum is to nourish the
developing embryo following fertilization.
During ____ in oogenesis, the tetrads of the
primary oocyte separate, and the dyads move toward
opposite poles.
anaphase I
During telophase I, the dyads at one pole
are pinched off with very little surrounding cytoplasm
to form the
first polar body
The ____ may or
may not divide again to produce two small haploid cells
first polar body
The other daughter cell produced by this first meiotic
division contains most of the cytoplasm and is called the
secondary oocyte
During this division, the cytoplasm of the secondary oocyte again divides unequally, producing an ___ and a
___ polar body. The ootid then differentiates into the
mature ovum
ootid
second
In others, including __, the first division of all
oocytes begins in the embryonic ovary but arrests in prophase I
humans
In others, including humans, the first division of all
oocytes begins in the embryonic ovary but arrests in ___ I
prophase
. Many years later, meiosis resumes in each oocyte
just prior to its __.
ovulation
is completed
only after fertilization in oogenesis
meiosis II
Will the genotype of the second polar body
(derived from meiosis II) always be identical to that of the
ootid? Why or why not?
uring meiosis I, homologous chromosomes undergo recombination (crossing over), leading to the exchange of genetic material between chromatids. This process creates genetic diversity, so the chromatids in the resulting daughter cells are not identical.
. In animals, meiosis leads to the formation
of ___
gametes
in plants, meiosis leads to formation of
spores
In
many fungi, the predominant stage of the life cycle consists of
haploid vegetative cells
haploid vegetative fungal cells arise through ___ and proliferate by ___ cell division
meiosis
mitotic
In multicellular plants, the
life cycle alternates between what stages
sporophyte stages
gametophyte
sporophyte stage is diploid/haploid
diploid (2n)
gametophyte stage is (haploid/diploid)
haploid
meiosis and mitosis constitute as ___ between the alternation of generations in plants
bridges
chromatin,
which consist of DNA and associated proteins, particularly
proteins called
histones
lectron microscopic observations of metaphase
chromosomes in varying degrees of coiling led Ernest
DuPraw to postulate the
folded-fiber model
Electron microscopic observations of metaphase
chromosomes in varying degrees of coiling led Ernest
DuPraw to postulate the folded-fiber model,
Ernest DuPraw
