Physical Basis of Heredity - Handout Flashcards
Actively dividing eukaryote cells pass through a series of stages known collectively as the
cell cycle
cell double checks the duplicated chromosomes for error, making any needed repairs
G2
each of the 46 chromosomes is duplicated by the cell
s phase
cellular contents, excluding the chromosomes, are duplicate
G1
Metabolic changes prepare the cell for division. At a certain point - the restriction
point - the cell is committed to division and moves into the S phase
G1 phase
DNA synthesis replicates the genetic material. Each chromosome now consists of
two sister chromatids
s phase
. Metabolic changes assemble the cytoplasmic materials necessary for mitosis and
cytokinesis.
g2 phase
e. A nuclear division (mitosis) followed by a cell division (cytokinesis)
m phase
s is a form of eukaryotic cell division that produces two daughter cells with the same
genetic component as the parent cell
mitosis
Chromosomes replicated during the S phase are divided
in such a way as to ensure that each daughter cell receives a copy of every chromosome. In
actively dividing animal cells, the whole process takes about
one hour
The replicated chromosomes are attached to a
mitotic apparatus
’ that aligns them and then
separates the sister chromatids to produce an even partitioning of the genetic material
mitotic apparatus
separation of the genetic material in a mitotic nuclear division
karyokinesis
separation of the cell cytoplasm in a cellular division
cytokinesis
In some single-celled organisms mitosis forms the basis of a
asexual reproduction
In diploid
multicellular organisms sexual reproduction involves the fusion of two __ gametes to produce a diploid zygote
haploid
five stages of mitosis
prophase
prometaphase
metaphase
anaphase
telophase
occupies over half of mitosis. The nuclear membrane breaks down to form a
number of small vesicles and the nucleolus disintegrates
prophase
structure known as the
___ duplicates itself to form two daughter centrosomes that migrate to opposite ends
of the cell. T
centrosome
. The centrosomes organise the production of microtubules that form the spindle
fibres that constitute the
mitotic spindle
s. Each replicated chromosome can now be seen to consist of two identical
chromatids
Each replicated chromosome can now be seen to consist of two identical
chromatids (or sister chromatids) held together by a structure known as the
centromere
The chromosomes, led by their centromeres, migrate to the ___ plane in the midline of
cell - at right-angles to the axis formed by the centrosomes
equatorial plate
The chromosomes, led by their centromeres, migrate to the equatorial plane in the midline of
cell - at right-angles to the axis formed by the centrosomes. This region of the mitotic spindle
is known as the
metaphase plate
The spindle fibres bind to a structure associated with the
centromere of each chromosome called a
kinetochore
The chromosomes align themselves along the metaphase plate of the spindle apparatus.
metaphase
The shortest stage of mitosis.
anaphase
s. The centromeres divide, and the sister chromatids of each
chromosome are pulled apart - or ‘disjoin’ - and move to the opposite ends of the cell, pulled
by spindle fibres attached to the kinetochore regions. The separated sister chromatids are now
referred to as
daughter chromosomes
The final stage of mitosis, and a reversal of many of the processes observed during prophase.
telophase
The final cellular division to form two new cells
cytokinesis
in plants, this forms during cytokinesis
cell plate
in animals, this form along the line of metaphase plate in cytokinessi
constriction of cytoplasm
s is the form of eukaryotic cell division that produces haploid sex cells or gametes
meiosis
a special cell division reduces the cell from diploid to haploid.
meiosis I
The homologous chromosomes pair and exchange DNA to form recombinant chromosomes.
what stage in meiosis
prophase I
Prophase I is divided into five phases:
leptotene
zygotene
pachytene
diplotene
diakinesis
chromosomes start to condense
what stage of prophase I
leptotene
homologous chromosomes become closely associated (synapsis) to form pairs of
chromosomes (bivalents) consisting of four chromatids (tetrads).
what stage in prophase I
zygotene
pairs of
chromosomes in zygotene
bivalents
crossing over between pairs of homologous chromosomes to form chiasmata
(sing. chiasma).
what phase in prophase I
pachytene
homologous chromosomes start to separate but remain attached by chiasmata
diplotene
s: homologous chromosomes continue to separate, and chiasmata move to the ends
of the chromosomes.
diakinesis
Spindle apparatus formed, and chromosomes attached to spindle fibres by kinetochores.
stage of meiosis I
prometaphase I
Homologous pairs of chromosomes (bivalents) arranged as a double row along the metaphase
plate. The arrangement of the paired chromosomes with respect to the poles of the spindle
apparatus is random along the metaphase plate.
metaphase I
This is a source of genetic variation through
random assortment, as the paternal and maternal chromosomes in a homologous pair are
similar but not identical
metaphase I
The number of possible arrangements is 2n, where n is the number
of chromosomes in a haploid set. Human beings have 23 different chromosomes, so the
number of possible combinations is
223
The homologous chromosomes in each bivalent are separated and move to the opposite poles
of the cell.
anaphse I
The chromosomes become diffuse and the nuclear membrane reforms.
what phase in meiosis I
telophase
The final cellular division to form two new cells, followed by Meiosis II. M
cytokinesis
Meiosis generates genetic diversity through (3)
the exchange of genetic material between homologous chromosomes during Meiosis I (pachytene)
the random alignment of maternal and paternal chromosomes in Meiosis I (metaphase I)
the random alignment of the sister chromatids at Meiosis II
what stage of Meiosis I does the first polar body form
teloophase I
which stage of Meiosis II does the egg cell turn into polar body and mature egg cell
cytokinesis
