D2.1 Cell & Nuclear Division Flashcards
what is the result of a single cell undergoing cycles of cell division
cells that make up a multicellular organism
parent cell
cell that divides to form daughter cells my mitosis or meiosis
daughter cell
cell produced when a parent cell undergoes cell division - mitosis or meiosis
what are the 2 types of cell division
mitosis and meiosis
cytokinesis
splitting of cytoplasm in a parent cell between daughters cells following division of nucleus
nuclear division
when the nucleus divides first during cell division
how does cytokinesis occur in animal cells
cleavage furrow is formed which separates daughter cells
where is a cleavage furrow formed
equator or centre of cell and pinches cell membrane together to split cytoplasm
when does a cleavage furrow form
when actin and myosin proteins form a contractile ring under plasma membrane
role of Golgi apparatus In cytokineses
forms vesicles of new cell wall materials which collect at equator or cell plate
how does cytokinesis occur in plant cells
when cell plate reaches cell wall of parent cell, new cell walls are produced
separates new daughter cells
what are cell plates formed off and what do they carry
formed of vesicles and carry carbohydrates
how is plasma membrane in daughter cell created
lipids and proteins fusing together
examples of unequal cytokinesis
oogenesis
spermatogenesis
budding in yeast
sizes of cytoplasm during cytokinesis
usually equal
with at least 1 mitochondria and 1 chloroplast
oogenisis definition
egg production in humans
one egg is formed as well as several small cells that don’t go forward with fertilisation
oocyte
immature egg cell - ovum
steps of oogenesis briefly
primary oocyte division to form one small polar body which is mainly just cytoplasm and a secondary oocyte which is the main one
division occurs again in both and total of 3 polar bodies and one ovum
polar bodies merge with ovum to form one big egg cell
why does ovum need a large cytoplasm
to provide nutrients and energy for the growing embryo
mitosis and meiosis purpose
division of nucleus of cell in eukaryotic cell
anucleate
cell without a nucleus
why is it important for nucleus of a cell to divide before cell division
to avoid production of anucleate cells
mitosis definition
daughter nuclei have the same number of chromosomes as the parent cell
what is mitosis used for
growth, repair of damaged tissues, replacement of cells and ASEXUAL reproduction
maintains chromosome number and genome of cells
diploid
cells with nuclei containing 2 sets of chromosomes
cells produced in mitosis will be —-
diploid
meiosis definition
daughter cell containing half the number of chromosomes of the parent cell
one chromosome of each parent present in nuclei
cells produced in meiosis will be —-
haploid
meiosis used
production of gametes - sperm and egg
generating genetic diversity
haploid notation
n
diploid notion
2n
interphase definition
the period between the nuclear divisions
replication of chromosomes takes place
phases in interphase
gap 1, gap 2, synthesis
chromatid
one of 2 copies of a chromosome after it has replicated, jointed together at centromere
centromere
constriction of chromosome, the region that becomes attached to the spindle fibres during nuclear division
condensation of chromosomes brief explanation
dna molecules are too long and need to fit in small nuclei
they become condensed by supercoiling to form chromosomes
how does condensation of DNA occur
through repeated coiling of dna molecule
histone protein role
packages dna into nucleosomes
how is supercoiling aided
is aided in eukaryotic cells by histone protiens and enzymes
histone definition
protiens that forms the structure of chromosomes and is used in chromosome condensation to form nucleosomes
nucleosomes definition
basic unit of eukaryotic chromosome structure, consisting of a ball of 8 histone protein molecules wrapped about by 2 coils of DNA
supercoiling
form of DNA in which the double helix is further twisted about itself within nucleosomes.
forming tightly coiled structure
how to chromosomes move during division
microtubules and microtubule motors move them
microtubules
tubular fibres that form part of the cytoskeleton of the cell
lengthen and shorten in order to make the chromosomal movement
4 main phases of mitosis (PMAT)
prophase
metaphase
anaphase
telophase
prophase simple
first stage where chromosomes condense
centrosomes move towards opposite poles
spindle fibres emerge from centrosomes
nuclear membrane breaking down into smaller vesicles
nucleolus dissapears
metaphase simple
centrosomes reach opposite poles
spindle continue to extend
chromosomes line at equator of spindle
spindle fibres reach chromosome and attach to centrosomes
- kinetochores
each sister chromatid is attached to a spindle fibre originating from opposite poles
anaphase simple
sister chromatids separate at centre
spindle fibres shorten
chromosomes pulled to opposite poles by spindle fibres
telophase simple
chromosomes at opposite poles and start decondensing
nuclear envelopes begin to reform around each set of chromosomes
spindle fibres break down
new nuclei form within each nucleus
meiosis phases
meiosis 1 and 2
what happens during m1
homologous pairs of chromosomes split to produce 2 haploid nucleus
how many chromatids in one chromosome
2
chromosome number in m1
halves from 2n to n in M1 -> reduction division
homologous chromosomes
pairs of chromosomes in a diploid organism that have similar genes, although not necessarily identical
bivalent
pair of homologous chromosomes held together by chiasma
chiasma
site of crossing over of segments of DNA between homologous chromosomes or non sister chromatids
crossing over
exchange of genetic material between bivalents
occurs between non-sister chromatids
results in a new combination of alleles on the 2 chromosomes
recombinant chromosomes
chromosomes which have been genetically changed due to crossing over
M2
between m1 and m2 no interphase
during m2 - chromatids separate to produce 4 haploid nuclei
each chromosome consists of a single chromatid
non disjunction occurs
occurs when chromosomes fail to separate correctly during meiosis
can occur in anaphase 1 or 2
non disjunction leading to
gametes being formed with an abnormal number of chromosomes
may end up with one extra copy of a particular chromosome or no copies of a particular chromosome
what happens if abnormal gametes are fertilised
chromosomes abnormality occurs as the diploid cell will have the incorrect numbers of chromosomes
example of non disjunction chromosome abnormality
Down syndrome or trisomy 21
what happens in Down syndrome
total of 47 chromosomes rather than 46
they have 3 copies of chromosome number 21
what is the impact of trisomy 21 or Down syndrome
varies between individuals
common features - physical growth delays
reduced intellectual ability
issues with sight or hearing
where else can trisomy 21 occur
in chromosomes 18 and 13
non disjunction definition
the failure of homologous chromosomes or sister chromatids to separate properly during meiosis
down syndrome definition
a congenital condition in which a person has an extra chromosome 21 as a result of non disjunction
karyotyping definition
a process which makes a diagram (karyotype) of chromosomes descending in size
karyotyping use
can be used to identify chromosomal abnormalities
how is genetically different offspring advantageous
for natural selection
increase in survival of species - evolving and adapting
genetic variation in populations of sexually reproducing species
what causes genetic differentiation
crossing over
mothers and fathers genes are exchanged into each others chromosomes
random orientation
orientation of bivalents when they line up at the cell equator (M1) determines which pole each chromosome gets attached to
combination formula
2^n
