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Site of male gamete formation= spermatogenesis. Produces testosterone. Testes (testis sing. ... has 4 chromosomes = 2N and creates 4 different possible gametes. ... – PowerPoint PPT presentation

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1
Lets Talk About Sex-ual Reproduction
  • Parts, their functions and Meiosis

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
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9
Test Yourself.so to speak! Name that part!
7
3
10
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9
2
4
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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
10
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.

11
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

12
Meiosis in Detail (contd)
  • Metaphase I
  • Homologous chromosomes line up at the equator of
    the cell
  • Spindle fibers attach to the chromosomes

13
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

14
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

15
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

16
Meiosis in Detail (contd)
  • Metaphase II
  • Chromosomes line up at the equator of the cell

17
Meiosis in Detail (contd)
  • Anaphase II
  • The sister chromatids separate and move to
    opposite sides of the cell

18
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!

19
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?

20
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

21
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

22
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

23
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

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
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