MEIOSIS I : PROPHASE I
Events occurring in the nucleus:
• Chromosomes coil and become individual
chromosomes, nucleolus and nuclear
• Homologous chromosomes come together
as pairs by synapsis forming a tetrad (Each
pair, with four chromatids)
• Non-sister chromatids exchange genetic
material through the process of crossing over
to ensure genetic variation.
• Centrioli move to opposite poles with spindle
fibers between them.
MEIOSIS II: TELOPHASE II
• Daughter chromosomes
has reached the poles.
• Two cells invaginate and
form 4 daughter
haploid cells (gametes)
• They uncoil and form
• Nuclear envelope and
nucleolus for around
• Centrioli for
SUMMERY OF MEIOSIS II
4. SIMILARITIES AND
MITOSIS AND MEIOSIS
Mitosis and meiosis both
• begin with diploid parent cells that
• have chromosomes duplicated during
the previous interphase.
However the end products differ.
• Mitosis produces two genetically
identical diploid somatic daughter
• Meiosis produces four genetically
unique haploid gametes.
Trisomy 21 produces a
characteristic set of symptoms,
characteristic facial features,
susceptibility to respiratory infections,
leukemia, and Alzheimer’s disease, and
• shortened life span.
The incidence increases with the age of the
B. ACCIDENTS DURING MEIOSIS
CAN ALTER CHROMOSOME
Nondisjunction is the failure of
chromosomes or chromatids to separate
normally during meiosis. This can happen
• meiosis I, if both members of a homologous
pair go to one pole or
• meiosis II if both sister chromatids go to
Fertilization after nondisjunction yields
zygotes with altered numbers of chromosomes.
THESE REARRANGEMENTS MAY
• a deletion, the loss of a chromosome
• a duplication, the repeat of a
• an inversion, the reversal of a
chromosome segment, or
• a translocation, the attachment of a
segment to a non-homologous
chromosome that can be reciprocal.
LIST OF SOURCES USED
• Mrs J.Williamsons 2014 sildes 3A FET MEIOSIS