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Reproduction

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Seminiferous tubules are inside each testis, and are where sperm are produced. ... Once sperm form they move into the epididymis, where they mature and are stored. ... – PowerPoint PPT presentation

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Title: Reproduction


1
Reproduction
  • BSCS Ch 12
  • Dragonfly Ch 39.3-4

2
Reproduction
  • The ability to reproduce is one of the unifying
    characteristics of all living things.
  • Sexual reproduction produces offspring that are
    genetically different from their parents.
  • Asexual reproduction produces offspring
    genetically identical to their parent.

3
Asexual Reproduction
  • Fission, budding, and fragmentation are some of
    the mechanisms that allow organisms to reproduce
    asexually.
  • Asexual reproduction allows an organism to
    rapidly produce many offspring without the time
    and resources committed to courtship, finding a
    mate, and mating.

4
Sexual Reproduction
  • In sexual reproduction new individuals are
    produced by the fusion of gametes to form a
    zygote.
  • Sperm are male gametes.
  • Ova (ovum singular) are female gametes.
  • Sexual reproduction offers the benefit of
    generating genetic variation among offspring,
    which enhances the chances of the population's
    survival.
  • Costs of this process include the need for two
    individuals to mate, courtship rituals, as well
    as a number of basic mechanisms described later.

5
Human Male Reproductive System
  • Human reproduction employs internal
    fertilization.
  • Gonads are sex organs that produce gametes.
  • Male gonads are the testes, which produce sperm
    and male sex hormones.

6
  • Testes are suspended outside the abdominal cavity
    by the scrotum, a pouch of skin that keeps the
    testes away from the body to be at an optimal
    temperature for sperm development.
  • Seminiferous tubules are inside each testis, and
    are where sperm are produced.
  • Sperm production begins at puberty with several
    hundred million sperm being produced each day.
  • Once sperm form they move into the epididymis,
    where they mature and are stored.

7
  • Sperm pass through the vas deferens which
    connects to a short ejaculatory duct that
    connects to the urethra.
  • The urethra passes through the penis and opens to
    the outside.
  • Secretions from the seminal vesicles add fructose
    and prostaglandins to sperm as they pass.
  • The prostate gland secretes a milky alkaline
    fluid.
  • The bulbourethral gland secretes a mucus-like
    fluid that provides lubrication for intercourse.
  • Sperm and secretions make up semen.

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10
Human Female Reproductive System
  • Female gonads are the ovaries, which produce eggs
    (ova) and female sex hormones.
  • The ovary contains many follicles composed of a
    developing egg surrounded by an outer layer of
    follicle cells. Each egg begins oogenesis as a
    primary oocyte.

11
  • A developing egg (secondary oocyte) is released
    each month from puberty until menopause, a total
    of 400-500 eggs.
  • After puberty the ovary cycles between a
    follicular phase (maturing follicles) and a
    luteal phase (presence of the corpus luteum).
  • The ovarian cycle lasts usually 28 days. During
    the first phase, the oocyte matures within a
    follicle. At midpoint of the cycle, the oocyte is
    released from the ovary in a process known as
    ovulation.

12
  • The secondary oocyte passes into the oviduct
    (fallopian tube or uterine tube). The oviduct is
    connected to the uterus.
  • The uterus has an inner layer, the endometrium,
    in which a fertilized egg implants.
  • At the lower end of the uterus the cervix
    connects the uterus to the vagina.
  • The vagina is the birth canal.

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15
The Menstrual Cycle
  • Menstrual cycles vary from between 15 and 31
    days.
  • The first day of the cycle is the first day of
    blood flow (day 0) known as menstruation.
  • During menstruation the uterine lining is broken
    down and shed as menstrual flow.

16
  • Around day 14 (midcycle) hormones trigger the
    maturation and ovulation of an egg.
  • If pregnancy does not occur, the drop in hormones
    causes the sloughing off of the inner lining of
    the uterus by a series of muscle contractions of
    the uterus.

17
Chromosome Numbers
  • All animals have a characteristic number of
    chromosomes in their body cells called the
    diploid (or 2n) number.
  • These occur as homologous pairs, one member of
    each pair having been acquired from the gamete of
    one of the two parents of the individual whose
    cells are being examined.
  • The gametes contain the haploid number (n) of
    chromosomes.

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19
Chromosome Numbers in Some Species (Diploid)
  • Buffalo 60
  • Cat 38
  • Human 46
  • Dog 78
  • Horse 64
  • Apple 34
  • Potato 48

20
Gamete Formation Meiosis
  • During the formation of gametes, the number of
    chromosomes is reduced by half (haploid), and
    returned to the full amount (diploid) when the
    two gametes fuse during fertilization.
  • Chromosomes that carry the same genes are termed
    homologous chromosomes.

21
Meiosis
  • Meiosis is a special type of nuclear division
    which segregates one copy of each homologous
    chromosome into each new "gamete".
  • Two successive nuclear divisions occur, Meiosis I
    (Reduction) and Meiosis II (Division). Meiosis
    produces 4 haploid cells.

22
Meiosis I
  • Interphase Before meiosis begins, genetic
    material is duplicated.
  • First division of meiosis
  • Prophase 1 Duplicated chromatin condenses. Each
    chromosome consists of two, closely associated
    sister chromatids. Crossing-over can occur during
    the latter part of this stage.

23
Crossing Over
  • When chromosomes pair in the early prophase of
    the first division of meiosis (Meiosis I), a
    crossover occurs between two non-sister
    chromatids.
  • This results in an exchange of genetic material
    between the maternal and paternal chromosomes.
  • The drawing provided shows a crossover between
    the non-sister chromatids of two, homologous
    chromosomes.

24
Crossing Over Animation
25
  • Metaphase 1 Homologous chromosomes align at the
    equatorial plate.
  • Anaphase 1 Homologous pairs separate with sister
    chromatids remaining together.
  • Telophase 1 Two daughter cells are formed with
    each daughter containing only one chromosome of
    the homologous pair.

26
Meiosis II
  • Second division of meiosis Gamete formation
  • Prophase 2 DNA does not replicate.
  • Metaphase 2 Chromosomes align at the equatorial
    plate.
  • Anaphase 2 Centromeres divide and sister
    chromatids migrate separately to each pole.
  • Telophase 2 Cell division is complete. Four
    haploid daughter cells are obtained.

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Meiosis Animation
29
Meiosis and Spermatogenesis
  • During meiosis, 4 sperm are produced by the two
    nuclear divisions.
  • These four sperm each have the haploid number of
    chromosomes.
  • The sperm are equal in size.

30
Meiosis and Oogenesis
  • Only one egg is produced by meiosis.
  • The ova need to contain a lot of nutrients (to
    get the embryo through its first set of
    divisions), so these cells need to be big. 
  • So, the cytoplasm is not divided equally between
    the 4 resulting cells.
  • The other cells are called polar bodies and they
    break down and disintegrate.

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32
Prokaryotic Reproduction
  • Prokaryotes are much simpler in their
    organization than are eukaryotes.
  • The usual method of prokaryote cell division is
    termed binary fission.
  • The prokaryotic chromosome is a single DNA
    molecule that first replicates, then attaches
    each copy to a different part of the cell
    membrane. When the cell begins to pull apart, the
    replicate and original chromosomes are separated.
  • Following cell splitting there are then two cells
    of identical genetic composition

33
Binary Fission
34
Sexual Reproduction in Plants
  • Many plants reproduce sexually.
  • The advantage to the plant is that its offspring
    have a selection of genes from two parents, so
    each individual's genes are different.
  • The offspring are not identical, and there is
    variety in the species.

35
Plant Reproductive Structures
  • Flowering plant's sexual organs consist of
  • Male the stamen, or male sex structure,
    consisting of a filament and a pollen-bearing
    anther at the tip
  • Female the pistil or female sex structure,
    consisting of ovary and ovule, style, and stigma
    at the tip. (The pistil is also sometimes called
    the carpel.)

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Pollination
  • An insect or the wind carries pollen grains from
    the anther of another flower.
  • The pollen grains land on the stigma and a pollen
    tube grows down through the style to the ovary.
  • The nucleus of the pollen grain passes down the
    tube. It fertilizes the egg cell inside the
    ovule.
  • The fertilized egg cell develops into an embryo.
    The ovary becomes the fruit and the ovule becomes
    a seed - from which (once dispersed) the
    offspring plant will grow.

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