Topic 4: The Cell Cycle Flashcards
Gametes
23 different chromosomes = haploid (n)
includes ova (eggs) + sperm
- sex cells
Somatic Cells
includes all cells of body except cells undergoing/resulting from meiosis
eg: muscle cell, nerve cell, etc.
46 chromosomes = diploid (2n)
= 23 homologous pairs
soma= body
Homologous Chromosomes
a chromosome pair (1 from each parent) that are identical in length, centromere position, and have genes for the same trait (e.g. eye colour) in the same location (locus)
Gene
a unit of heredity
= a region of DNA which contains information for synthesis of proteins
*how we pass on genetic info from one person to the next
alleles
different versions (alleles) of that gene that code for different versions of that trait.
§ e.g. blue eyes (chromosome from Dad), brown eyes
(chromosome from Mom)
What does each somatic cell contain?
23 different chromosome pairs
23 chromosomes from mom (ovum) paired with 23 chromosomes from dad (sperm)
= 46 chromosomes (diploid/2n somatic cell)
autosomal chromosomes (autosomes)
1 to 22
¦ contain genes for somatic characteristics
¦ e.g. hair and eye colour, height, etc
¦ each autosomal chromosome pair is not identical, but
equivalent= homologous chromosomes
sex chromosome
23
¦ contain genes that determine sex, XX=F XY=M
¦ X or Y from Dad
¦ X from Mom
What is the purpose of mitosis?
for growth + repair of tissues
to produce somatic cells
What does mitosis result in?
2 genetically identical daughter cells
List the stages of the cell cycle:
1) Interphase
2) Mitotic (M)/Cell Division phase
List the stages within Interphase:
G1,
S,
G2 phases
Interphase
chromosomes present as chromatin
normal cellular metabolic activities occurring e.g. protein synthesis
G1 Phase
growth, metabolism
centrosome replication begins
Note: in some cells that do not divide again once mature, (i.e. remain
in G1) – in these cells it is termed G0 phase
¦ e.g. nerve + some muscle cells
S Phase
chromosomes replicate, but are still present as chromatin (not individually visible)
ALWAYS occurs before division (mitosis and meiosis)
kinetochore proteins are produced
sister chromatids
replicates formed during S phase
centromere
area of DNA where sister chromatids attach to one another
kinetochore proteins
(produced during S phase) attach to each centromere to form the kinetochore
kinetochore
protein + DNA complex,
1/chromatid meaning 1 on each side)
site of attachment of spindle microtubules
G2 Phase
growth, metabolism
production of enzymes & other proteins needed for cell division
centrosome replication completed
What does the Mitotic Phase involve?
a) mitosis
b) cytokinesis
mitosis
= division of nuclear material (chromosomes)
4 phases, but continuous cycle!
i. Prophase
ii. Metaphase
iii. Anaphase
iv. Telophase
cytokinesis
division of cytoplasm
when mitotic phase ends:
mitosis & cytokinesis complete
daughter cells go into interphase (G1)
cycle starts over
Prophase
chromosomes condense (thicken, coil) from chromatin form - become individually visible
nucleoli disappear and nuclear envelope breaks up
centrosomes move to either pole
microtubules form spindle apparatus (starting at centrosomes) + attach to kinetochore proteins (called kinetochore microtubules)
Spindle moves chromosomes toward cell equator
Metaphase
46 chromosomes line up on cell equator
Anaphase
as the spindle microtubules shorten, the kinetochores are pulled away from each other – causing separation of centromeres, which results in separation of the chromatids
46 chromatids migrate to each pole
cytokinesis (division of cytoplasm) begins
Telophase
chromosomes uncoil to chromatin
nucleoli, nuclear envelope reappear
spindle disassembles
cytokinesis completes (or may end after telophase ends)
Meiosis
reproductive nuclear division
meiosis produces
gametes (= ovum + sperm)
1 cell (diploid, 2n) produces
4 genetically dissimilar gametes (each haploid, n)
What are the stages of Meiosis
involves: interphase (G1, S, G2) followed by 2 cell divisions:
1) Meiosis I, immediately
followed by
2) Meiosis II
between meiosis I + II = interkinesis NOT interphase (no DNA replication)
Meiosis I
(reduction division = 2n to n)
events same as in mitosis
Prophase I
i. homologous chromosomes attach together = tetrads (4 chromatids in a
row)
ii. crossing over occurs
• piece of 1 chromatid exchanges with matching piece from a chromatid of the homologous chromosome i.e. non-sister chromatid
- acts to increase genetic diversity
- e.g. you pass on your dad’s black hair with your mom’s blue eyes
Metaphase I
23 tetrads line up along cell equator
Anaphase I
tetrads (homologous chromosome pairs) separate and migrate to opposite poles
i.e. 1 homologous chromosome (with 2 sister chromatids) goes to each
pole chromatids DON’T separate
Telophase I
same as mitosis telophase
spindle disassembles
nucleolus and nuclear envelope reappear
chromosomes uncoil to chromatin
After Meiosis I and cytokinesis:
each new cell has 23 different chromosomes (½ the number of Xms) = haploid (n)
these cells DO NOT have homologous chromosomes
chromosome 1 – 23 from Mom OR Dad (randomly segregated)
Meiosis II
same as mitosis except with 23 chromosomes instead of 46
a) prophase II
b) metaphase II - 23 chromosomes line up at equator
c) anaphase II - 23 chromatids migrate to each pole
d) telophase II
¦ cytokinesis – same for mitosis/meiosis (begins in anaphase/anaphase I/anaphase II,
and continues through telophase/telophase I/telophase II)
Where does meiosis take place in the body?
In the gonads
ovaries= female
testes= males
Why meiosis?
Need to turn diploid germ cells into haploid gametes
Fertilization
spermatozoon (n) contacts and penetrates 2o oocyte (n) = fertilization
triggers completion of meiosis II in 2o oocyte
– forms ovum (egg)
then ♂ + ♀ pronuclei unite
new cell = zygote (2n)
pronucleus
nucleus of sperm/egg post-fertilization but prior to fusion
