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Question 1: Define the terms below:
a)

Leading DNA strand
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b)

Lagging DNA strand
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Since
the two strands run parallel to each
other, the lagging strand proceeds in
a 5’-3’ direction
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How behavioural and physical
characteristics, including medical
conditions, are transmitted down
from a parent to their offspring by
genes in the chromosomes
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One chromosome from each parent
representing a pair based on physical
similarities

A membrane bound organelle active
during DNA replication consisting of
two centrioles
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Cells that contain half the number of
chromosomes (one set)
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They are only found in sex
cells
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They contain all pairs of homologues
chromosomes (total of 46) and they
are being produced via mitosis
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f)

Gametogenesis
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g)

Apoptosis
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Centrosome
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Mitosis functions to replace grow and
repair in cellular organisms
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b)

Type of reproduction
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Meiosis is sexual reproduction and
includes two cell divisions and produces
germ cells which are the cells giving rise
to the gametes
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Mitosis: Two identical daughter cells

cytokinesis
Meiosis have two main stages and that is
meiosis I and II
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These
daughter cells are not identical
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In mitosis exact genetic duplicates are
being made with two sets of
chromosomes, one being maternal and on
being paternal
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Metaphase II
Anaphase II

e)

Stages (phases)
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(Encyclopaedia Britannica, 2014)
Anaphase
(Encyclopaedia Britannica,2015)
Telophase

Question: Explain the following sentence: “Alterations that occur in the somatic cells
rather than the germline cells will not be passed on to offspring
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They are being replicated via mitosis
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These cells exist only in the ovaries (females) and testes (male)
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This occurs in a single cell developing somatic tissue
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(Guttman, Griffiths, Suzuki, Cullis, 2015, p
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If that gamete fuses with another
in fertilisation it will be passed down to the offspring and that organism will have the mutation in all
their cells since cells differentiate from the first two gametes
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However, this does not indicate the mutation will be expressed in the organism
that contains it
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Question 4: Read the Text extract 1 and address Q4
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Even two
siblings who come from the same parents have different genetic make-ups
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Q4
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The law of independent assortment refers to the alleles of two genes, and how they assort
independently when forming gametes
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Fertilization creates the genetic diversity when the paternal and maternal contributes with a unique
set of genes that have been randomly selected to the zygote
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The new combination can
determine new traits in the parent’s offspring
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66)
When the homologues pairs of chromosomes get oriented at random along the equator in
metaphase I it can be either one of the paternal or the maternal homologue that gets orientated
towards either pole of the cell
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(IB Guides, 2012)
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1): Analyse the Diagram 1 and then address Q5
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3

Q5
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In your answer, you
are expected to briefly explain what theses stages are and why they cannot be
skipped or changed in order for cell division to occur in an adult cell
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The cell is growing by
increasing its volume in cytoplasm and increases its number of organelles
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G0 which is associated with G1 and it doesn’t always occur but it is
when the cell will stop dividing and leave the cell cycle either temporary or permanent
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Before the restriction point’s cells are able to leave the
division and enter G0
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Then the cycle moves to G2 (gap 2) where metabolic changes occur and assembles the
materials that will be needed for mitosis and cytokinesis
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In the M phase nuclear division takes place in the form of mitosis and after that the cell divides in
cytokinesis
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(Thompson, 2015)
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This is why the stages occur in a specific order, if
there is an error in the cell cycle it may result in cancer
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Question 6: The graph below illustrates changes in the DNA content of the nucleus
during the process of meiosis
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Q6
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The germ cell contains 2 copies of chromosomes before it is being replicated, one copy being
maternal and the other being paternal
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“S” shows the DNA in each chromosome is being replicated before mitosis begins and the DNA
content doubles
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It is important that the replication
is precise otherwise genetic abnormalities can occur
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In M2 the DNA content is once again divided by half when the chromatids get
separated
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The chromosomes must be halved in order maintain the number in following
generations
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(Nature education,
2014)

Question 7 Carefully read and analyse the Text extract 2, and then address Q7
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Amazingly, DNA replication is
accomplished with an average of only 1 error per billion (10 9) nucleotides”
(EHD, 2015)
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Briefly discuss the information above, highlighting the importance of checkpoints
in the cell cycle to prevent mistakes that occurred during the interphase or in mitosis
from being passed forward to every new cell produced
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Towards the end of the G1 phase it will be evaluated if the DNA is damaged in any way, if the
conditions looks promising the cell will commit to the cell cycle
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g
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The cell can then proceed to DNA
replication and enter the S phase
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After
the restriction point the extracellular growth factors will no longer be required since it has now been
replicated
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If the cell’s condition is proven
sufficient it will continue into the M phase
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In the M phase it checks to determine that all the sister chromatids are attached to the spindle
microtubules in the correct way, then the cell proceeds to anaphase
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If this happens that mutation can be passed to every new cell the abnormal cell
produces
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This is referred to as the G0 phase
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It delays anaphase until the microtubules have caught all kinetochores
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Text extract 3:
“The duration of the cell cycle phases varies considerably in different kinds
of cells
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Shorter cell cycles (30
minutes or less) occur in early embryo cells shortly after fertilisation of the
egg
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Diagram 2: Comparison of early embryonic cell cycle with somatic cell cycle (Nature
Education, 2000)
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After considering the information above, compare and contrast the biological
importance of mitosis in the early human embryo and in the adult human
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The first mitotic divisions start after an ovum and spermatozoon forms a zygote by fusing together
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The blastocysts inner
cell mass consists of embryotic stem cells
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The mitosis in the early
embryo takes place at such rapid pace because the zygote differentiates to a fully functional
organism in approximately 40 weeks
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Because gap and intervening phases doesn’t occur here, it intensifies the quantity of cells and DNA
content
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In contrast to the early embryo where the primary purpose
is to allow for a rapid growth in the organism in order to develop into an adult; this is at frequent
bases
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(Libal, 2015)
...
(2014)
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Available:
http://www
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com/science/mitosis
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2
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(2015)
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Available:
http://www
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com/science/meiosis-cytology
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1
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B
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Griffiths, DD
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Cullis (2015)
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London:
Oneworld
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IB Guides
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Meiosis
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com/biology/notes/meiosis-
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Noelle Thompson
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When Happens When Mitosis Goes Wrong and in Which
Phase Will It Go Wrong?
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synonym
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html
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6
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(2014)
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Available: http://www
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com/scitable/topicpage/replication-anddistribution-of-dna-during-meiosis-6524853
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7
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Foster, Paige Yellen, Limei Xu, Mahesh Saqcena
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Regulation of
G1 Cell Cycle Progression
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ncbi
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nih
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Last accessed Jan 6th
2016
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Sandra E
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(2005)
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Available: http://www
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nlm
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gov/pmc/articles/PMC551473/
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9
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(2015)
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Available: http://classroom
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com/stage-life-mitosis-occurrapidly-17281
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Last accessed 6th Jan 2015
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