1. Chapter 8 Part 2
Meiosis

2. Cancer is uncontrolled cell division
Cell cycle control is lacking in cancer cells
• The cell cycle control system ensures that the
stages occur in order and only when the
previous stage has been successfully
completed.

3. • G1 checkpoint – cell enters G0 or, if DNA is
damaged and cannot be repaired, apoptosis
occurs.
• G2 checkpoint – mitosis will occur if DNA has
replicated properly. Apoptosis will occur if DNA
is damaged and cannot be repaired.
• M checkpoint – mitosis will not continue if
chromosomes are not properly aligned
• Apoptosis – programmed cell death. Cell pulls
away from other cells, starts to break apart, and
the pieces are engulfed by white blood cells or
neighboring cells. This allows organisms to take
shape – tadpoles losing their tail, fingers and
toes in humans losing webbing as an embryo.

4. Development of cancer (carcinogenesis)
• Mutations due to environmental assaults can
result in abnormal growth
• Tissues with a high rate of division are more
susceptible
• If a cell with a mutation is allowed to divide, it
becomes more abnormal with each generation
• Cancers are classified according to tissue of
origin
– Carcinomas – tissues that line organs
– Sarcomas – muscle, bone, cartilage
– Leukemias - blood

5. Cancer cell characteristics
• Lack differentiation – nonspecialized, do
not contribute to the functioning of a body
part
• Have abnormal nuclei – enlarged and may
have abnormal number of chromosomes
• Form tumors
• Undergo angiogenesis and metastasis
– Angiogenesis – formation of new blood
vessels, these supply nutrients and oxygen to
the cells
– Metastasis – cancer cells begin new tumors
far from the primary tumor

6. Meiosis reduces the chromosome
number
Homologous chromosomes separate during meiosis
• During meiosis I, homologous chromosomes line up side
by side (synapse)
• After cell division, the daughter cells are haploid
• Interkinesis – time between meiosis I and meiosis II
• During meiosis II, sister chromatids are separated
resulting in 4 haploid daughter cells
• Daughter cells mature into gametes (sperm and egg)
• Fertilization – bringing together of sperm and egg,
resulting in diploid zygote

8. Synapsis and crossing over occur
during meiosis I
• Synapsis – homologous chromosomes
line up side by side
• Crossing over – homologous
chromosomes (homologues) exchange
genetic material. Increases genetic
variability of the daughter cells

9. Sexual reproduction increases
genetic variation
• Homologues line up
independently at
equator
• At the end of meiosis
any short
chromosome can end
up with any long
chromosome

10. • Fertilization – gametes carry different
genetic information due to independent
assortment and crossing over. The same
couple can have offspring that are very
different genetically.
• Advantages of genetic variation
– Some offspring have a better chance of
survival that others
– In warmer environments, dogs with short hair
may have an advantage over dogs with long
hair

11. Meiosis requires meiosis I and
meiosis II
• Prophase I – chromosomes have
duplicated, homologues pair
during synapsis and crossing
over occurs
• Metaphase I – homologues align
independently at the equator
• Anaphase I – homologues
separate and are pulled toward
the poles
• Telophase I – nuclei reform
• Interkinesis – between meiosis I
and meiosis II – chromosomes
still have sister chromatids

12. • Prophase II – cells have
one chromosome from
each pair of homologues
• Metaphase II –
chromosomes align at the
equator
• Anaphase II – sister
chromatids separate and
become daughter
chromosomes
• Telophase II – nuclei
reform, cytokinesis takes
place
• Daughter cells – 4 haploid
daughter cells

13. Life cycles are varies
• Asexual reproduction
– Prokaryotes
– Offspring are genetically identical to parent
• Sexual reproduction
– Eukaryotes
– Two parents, involves meiosis and mitosis,
offspring are genetically different from parent

14. 3 possible life cycles
• Haploid life cycle
– Algae
– Adult is haploid
– Asexual reproduction if environment is stable
– Sexual reproduction occurs when environment is unstable,
produces zygote that can survive bad weather
• Alternation of generations life cycle
– Plants
– Meiosis produces haploid gametes
– Fertilization results in diploid cells
• Diploid life cycle
– Animals
– Haploid egg and sperm produced
– Fertilizes to produce diploid zygote

15. Meiosis can be compared to
mitosis
Meiosis
• 2 nuclear divisions
• 4 daughter cells
• Haploid
• Genetically different
Mitosis
• 1 nuclear division
• 2 daughter cells
• Diploid
• Genetically identical

16. Chromosome anomalies can be
inherited
Nondisjunction causes chromosome number
anomalies
• Polyploid – 3 or more complete sets of
chromosomes. This is common in many crops
and fruits.
• Aneuploid – different number of a particular
chromosome.
– Monosomy – one of a particular chromosome (2n – 1)
– Trisomy – three of a particular chromosome (2n + 1)

17. • Nondisjunction
– During meiosis I –
homologues do not
separate and both go to the
same daughter cell
– During meiosis II – sister
chromatids do not separate
and both go to the same
daughter cell
– Occurs in plants and
animals. Lethal most of the
time in animals, but those
with trisomy are more likely
to survive that monosomy.
Sex chromosome
aneuploids have a better
chance of surviving that do
autosomal aneuploids.

18. Chromosome number anomalies
can be observed
Trisomy 21 (Down syndrome)
• Autosomal chromosome
• Easily recognizable physical and
mental characteristics
• Chances of a woman having a
child with Down syndrome
increases with age.
• Most children with Down
syndrome are born to mothers
younger than 40, because that
age group is having the most
babies.

20. • Turner syndrome
(XO) female with one
X
• Before and after
surgery to remove
neck webbing.

21. • Trisomy (XXX) female with 3 X chromosomes.
Lack symptoms.
• Klinefelter syndrome (XXY) male. Lack some
male characteristics, very long arms and legs.
• (XYY) males appear normal

22. Chromosome structure anomalies
can also be observed
• Can lead to various
syndromes
• Deletion – loss of part of a
chromosome
• Duplication – a particular
chromosome segment
appears more than once in
the same chromosome
• Inversion – reversed
sequence in part of a
chromosome
• Translocation – movement of
a chromosome segment
from one chromosome to
another

23. Syndrome examples
• Williams syndrome – deletion
• Cat’s cry syndrome – deletion
• Down syndrome – 5% of the time due to
translocation
• Certain types of cancer - translocation

24. http://media.pearsoncmg.com/bc/bc_0media_bio