1
Lets Talk About Sex-ual Reproduction

• Parts, their functions and Meiosis

?Genome British Columbia, 2004
www.genomicseducation.ca
2
The Human Life CycleWhy do we reproduce?
http//www.biosci.uga.edu/almanac/bio_103/notes/ap
r_4.html
3
Sexual Reproduction

• 2 parents are required and can produce 1 or more
  offspring that are genetically different from
  either parent
• Benefits creates genetic variation in a
  population which allows for evolution and
  adaptation as well as being able to battle
  parasites, viruses and bacterial pathogens some
  species find it an enjoyable past-time! It also
  ensures your genes are passed on, like leaving
  something of yourself behind when you are gone!
• Drawbacks requires more time and energy,
  produces smaller numbers of offspring generally,
  requires both parents be in the same place at the
  same time (must find a mate!)
• How does it happen?? You must learn a bit about
  the human structures first..

4
Male Reproductive Organs
5
Male Reproductive Structures and their Functions
Structure Function
Testes (testis sing.) Site of male gamete formation spermatogenesis Produces testosterone
Scrotum Holds the testes outside the body
Epidydimus Where sperm is stored
Vas deferens Sperm travels through here
Seminal Vesicle Creates seminal fluid which adds nutrients to semen
Cowpers Gland Creates alkaline fluid to counteract acidity in vagina
Prostate Gland Creates secretions for semen
Urethra Semen and urine travel through this to the outside
6
Female Reproductive Organs
7
Female Reproductive Structures and their Functions
Structure Function
Ovary Site of oogenesis and estrogen and progesterone production
OviductsFallopian Tubes Site of egg fertilization, egg travels through to uterus if not fertilized
Uterus Zygote implants here, embryo grows via placenta
Cervix Creates mucin strands for sperm to travel up into uterus
Vagina Receives sperm, birth canal for fetus
Clitoris Sensory organ similar to glans penis
8
Test Yourself.so to speak! Name that part!
7
3
10
6
9
2
4
5
8
1
1. Testis 2. Cowpers Gland 3.Vas Deferens 4.
Urethra 5. Epididymus 6. Oviduct 7. Ovary
8. Vagina 9. Uterus 10. Prostate Gland
9
Meiosis- The Process of making Gametes

• OVERVIEW
• 1st Division is very important as it reduces the
  numbers of chromosomes by half .
• Prophase I has the homologous chromosomes
  (chromosomes that appear identical to one another
  because they carry the same genes, one comes from
  our mom, and the other comes from our dad.)
  crossing over to exchange material
• Metaphase I have the homologous pairs line up at
  the equator of the cell and in Anaphase I, the
  homologous chromosomes separate and thus reducing
  the chromosome number in each cell.
• 2nd Division of Meiosis is exactly like mitosis,
  except that 2 cells start off in prophase 2 and
  you end up with 4 daughter cells that are
  completely different from each other.

10
Meiosis in Detail

• Prophase I
• Homologous chromosomes thicken and attach to each
  other in a chiasma (chiasmata- plural)
• Crossing Over occurs between homologs
• The nuclear envelops disintegrates
• The spindle fibers form from centrioles that move
  to the poles of the cell

11
Meiosis in Detail (contd)

• Metaphase I
• Homologous chromosomes line up at the equator of
  the cell
• Spindle fibers attach to the chromosomes

12
Meiosis in Detail (contd)

• Anaphase I
• Homologous chromosomes separate from each other
  and go to opposite poles of the cell
• Sister chromatids do not separate

13
Meiosis in Detail (contd)

• Telophase I
• Spindle fibers disappear
• Nuclear envelope may reappear
• Cytokinesis occurs to create 2 cells having half
  the number of chromosomes of the parent cell

14
Meiosis in Detail (contd)

• Meiosis II
• Prophase II
• Same as mitosis nuclear envelop
  disintegrates
• Spindle fibers form and attach to each
  chromatid and the centromere of the chromosome

15
Meiosis in Detail (contd)

• Metaphase II
• Chromosomes line up at the equator of the cell

16
Meiosis in Detail (contd)

• Anaphase II
• The sister chromatids separate and move to
  opposite sides of the cell

17
Meiosis in Detail (contd)

• Telophase II
• Nuclear envelopes reform and the spindle fibers
  disappear
• Chromosomes relax into fine threads
• Cytokinesis occurs
• BOTTOM LINE
• 4 different haploid cells have been formed!

18
Meiosis Genetic Variability?

• This cell has 4 chromosomes 2N and creates 4
  different possible gametes.
• What happens when there are 6 chromosomes? How
  many possible different gametes can arise?
• Does it matter if there is crossing over, or not?

19
Meiosis Spermatogenesis Making Sperm

• Notice that the outcome of this meiosis shows no
  crossing over, only a shuffling of chromosomes
  and the maturation of sperm (crossing over occurs
  more often than not occurring at all)
• There are 4 different cells that arise from
  meiosis each having only ½ the original amount
  of DNA

20
Meiosis Oogenesis Making Eggs

• There are still 4 different cells created,
  however, only 1 of them is used for fertilization
• note the first meiotic division starts at
  ovulation, while the second meiotic division is
  not complete until fertilization occurs!
• females are born with a preset number of
  potential gametes prior to birth

21
Comparing Mitosis and Meiosis

• Mitosis
• 1. begins with one cell
• 2. creates 2 identical diploid cells
• 3. has only 1 stage of division
• 4. DNA replicates before mitosis begins
• 5. Occurs in all body cells at some point of
  life
• 6. Crossing over is a rare event

• Meiosis
• 1. begins with one cell
• 2. creates 4 different haploid cells
• 3. has 2 stages of division
• 4. DNA replicates before meiosis begins
• 5. Occurs only in sex cells
• 6. Involves crossing over as a normal event

22
Sexual vs Asexual Reproduction

• Sexual
• 1. Requires two parents
• 2. Creates offspring that are different than the
  parents
• 3. Process occurs by meiosis, fertilization and
  then birth
• 4. Harmful pathogens cannot wipe out entire
  populations as there is a variety in genetic
  make-up
• 5. Increases the organisms chance of survival
  and evolution
• 6. Usually occurs in organisms that are more
  complex
• 7. Requires more energy and time in raising the
  offspring

• Asexual
• 1. Requires only one parent
• 2. Creates offspring that are identical to the
  parent
• 3. Process may be by mitosis, spore formation,
  budding etc.
• 4. Harmful pathogens can wipe out entire
  colonies of organisms due to the same genetic
  make-up e.g bananas!
• 5. May decrease the organisms evolutionary
  capacity
• 6. Usually occurs in organisms that are less
  complex
• 7. Requires less energy and time in raising the
  offspring

23
When Meiosis goes wrong?

• What could possibly go wrong in meiosis?
• Often mistakes occur Where?
• -in the first division, but can occur in the
  second division as well, usually in egg formation
• -

24
Bibliography and Credits

• http//www.biosci.uga.edu/almanac/bio_103/notes/ap
  r_4.html
• Audesirk et al. Biology Life on Earth. Sixth
  Edition. Prentice Hall. 2002.
• http//www.accessexcellence.org/RC/VL/GG/index.htm
  l
• http//www.grad.ttuhsc.edu/courses/histo/notes/fem
  ale.html
• http//www.biosci.uga.edu/almanac/bio_103/notes/ap
  r_8.html
• http//www4.ncsu.edu/unity/users/b/bnchorle/www/in
  dex.htm