Biology 30 – Ch. 21 Meiosis and Sexual Reproduction Notes
Asexual Reproduction
• ________________________, no union of DNA
• Offspring are _____________________ and to the parent
Advantages:
• ____________________________________________.
• Identical “If well adapted, why change?”
Disadvantages:
• No ___________, therefore no _________, no evolution and
___________________.
Examples:
• Binary fission, budding, regeneration, spores and vegetative
propagation.
Sexual Reproduction
• Any ______________ of DNA from _______________.
• Offspring are __________________ each other and different from
________________
Advantages:
• Variety, therefore _______________________________.
Disadvantages:
• More ______________, more ______________, special circumstances
required.
Examples:
1. __________________ – union of DNA ____________ sex cells
(_________). Bacteria, paramecium, Rhizopus.
2. ________________ – gametes same size and shape but different DNA.
3. _____________ – gametes are ____________, ________ egg cell
stores food and __________motile sperm cell.
Eg. Flowering plants, all animals - people, elephants, bears, and puppy dogs
MEIOSIS
• Why is the process necessary?
1. To reduce the chromosome number to _______________
__________so that the proper number can be restored by ___________
to produce a ______________________.
• Body Cell Human – ____________________________.
• Sperm & Egg – _______________________________.
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Biology 30 – Ch. 21 Meiosis and Sexual Reproduction Notes
• One chromosome from each pair = ________________.
2. ________________________.
Where does it occur?
• Animals – __________________________
Plants
• Male – __________________ in the anther of the stamen
• Female – ______________ in the ovule in the ________.
Interphase I
• Similar to ___________________.
• ________________________ replicate.
• Each duplicated __________________ consist of two identical sister
______________ attached at their _________________.
• _______________________ pairs also replicate.
Meiosis I (four phases)
• Cell division that ____________the chromosome number by
___________________.
• Four phases:
a.
____________________
b. ____________________
c.
____________________
d. ____________________
Prophase I
• ____________________________phase (90%).
• Chromosomes __________________.
• __________________ chromosomes come together to form a
______________.
• __________________ is two chromosomes or four ________________
(sister and non sister chromatids).
• This process of homologues pairing up is called ______________
Crossing Over
• Crossing over (variation) may occur between non sister chromatids at
the ________________________.
• Crossing over: segments of non sister chromatids _____
____________________ to the other chromatid.
• ___________________ are the sites of ______________.
Metaphase I
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Biology 30 – Ch. 21 Meiosis and Sexual Reproduction Notes
Chromosomes line up at the metaphase plate.
Anaphase I
• Homologous chromosomes separate and move towards the poles.
• Sister chromatids ______________ at their centromeres.
Telophase I
• Each pole now has ______________________________.
• ____________________occurs and two haploid daughter cells are
formed.
Meiosis II
• ______________________________
(or very short - no more DNA replication)
Remember: Meiosis II is similar to mitosis
Prophase II
• same as prophase in mitosis
Metaphase II
 same as metaphase in mitosis
Anaphase II
• same as anaphase in mitosis
• _________________________________________.
Telophase II
• Same as telophase in mitosis.
• ____________________________________________.
• ________________________________________.
• Remember:
__________________________________.
• Gametes = __________________________________.
Gametogenesis
• Refers to the production of ______________________________________.
• In mammals the male process of gametogenesis is called ______________.
In female mammals the process is called ______________________.
• Both processes involve the meiotic division of ________________ cells to
form _______________________________.
Spermatogenesis
• Spermatogenesis is the process of __________________ development.
• This process occurs in the ________________ of the sexually mature male.
• The sites of spermatozoa production are the ________________________.
• The spermatozoa originate from precursor cells called ________________.
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Biology 30 – Ch. 21 Meiosis and Sexual Reproduction Notes
• Spermatogenesis is unique because it involves both ___________________
and ___________________________________.
• The spermatogonia divide by _______________________ several times
creating ______________ cells that eventually undergo ____________ to
create the _______________________ which eventually mature into sperm
cells.
• These repeating mitotic stages explain why several hundred million sperm
cells can be produced every day.
Oogenesis
• Egg formation takes place in the ___________________.
• In contrast to males, the initial steps in egg production occur prior to birth.
• Diploid stem cells called ______________ divide by mitosis to produce
more ______________ and ______________. By the time the fetus is 20
weeks old, the process reaches its peak and all the oocytes that she will
ever possess (6-7 million of them) have been formed.
• By the time she is born, 1-2 million of these remain. Each has begun the
first steps of the first meiotic division (meiosis I) and then stopped.
• No further development occurs until years later when the girl becomes
sexually mature.
• Then the ___________________ recommence their development, usually
one at a time and once a month.
• The primary oocyte grows much larger and completes the _____________,
forming a large ___________________ and a small _______________ that
receives little more than one set of chromosomes.
• Which chromosomes end up in the egg and which in the polar body is
entirely a matter of chance.
• In humans (and most vertebrates), the first polar body ________________
_________________, but the secondary oocyte does proceed as far as
metaphase of meiosis II and then stops.
• Only if ___________________ occurs will meiosis II ever be completed.
Entry of the sperm restarts the cell cycle.
External Fertilization
• External fertilization occurs mostly in __________________________ and
requires both the male and the female to ___________________________
____________________________________________________.
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Biology 30 – Ch. 21 Meiosis and Sexual Reproduction Notes
• An advantage of external fertilization is that it results in the production of a
____________________________________________.
• One disadvantage is that environmental hazards such as predators greatly
reduce the chance of surviving into adulthood.
• Amphibians and fish are examples of animals that reproduce this way.
• Very little parental care is taken to ensure survival. Because so many
offspring are produced parental protection is impossible.
• Another disadvantage of external fertilization is that reproduction is tied to
______________________. If an environment experiences __________
________________the gametes do not have the water required for egg
development.
Internal Fertilization
• Internal fertilization is a form of animal fertilization that occurs _________
the female body. This is distinct from external fertilization which occurs in
_______________________.
• The union of spermatozoa and ovum occurs inside of the female but the
embryo doesn't necessarily stay there.
• _______________organisms, like most insects, chickens, turtles, and most
snakes lay eggs that continue to develop after being laid, and hatch later.
• __________________ organisms, like garter snakes, and the Madagascar
Hissing Cockroach, have eggs (with shells) that hatch as they are laid,
making it look like live birth.
• ______________ organisms, like humans, whales, kangaroos and all other
mammals bear their young live.
• The developing young spend proportionately more time within the female's
reproductive tract.
• The young are later released to survive on their own, with varying amounts
of help from the parent(s) depending on the species.
The advantages of internal fertilization are:
• reproduction is not determined by the ______________________________
• embryos are ________________________, nesting mothers invest time
into raising of offspring
• _____________________________, due to the protection by parents
• ______________ are deposited precisely where _________________ takes
place.
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