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Animal Reproduction


Animal Reproduction AP Biology Chapter 46 Campbell 6e Ppt courtesy of Tracy Jackson Reproduction There are 2 modes of ... – PowerPoint PPT presentation

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Title: Animal Reproduction

Animal Reproduction
  • AP Biology Chapter 46
  • Campbell 6e

Ppt courtesy of Tracy Jackson http//
  • There are 2 modes of reproduction in the animal
  • Asexual creation of individuals whose genes
    come from one parent by mostly mitotic cell
  • Sexual creation of individuals from the fusion
    of gametes to form a zygote.

Asexual Reproduction
  • Fission, budding, and fragmentation are some of
    the mechanisms that allow organisms to reproduce
  • Fission the division of bacterial cells.
  • Budding new individuals splitting off of the
  • Fragmentation breakage of the organism into
    several parts to form new organisms. (accompanied
    by regeneration of new body parts.)

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  • It is advantageous in a constant environment
    because a large number of offspring can be
    produced in a short time.
  • Flatworms can divide into 2 halves each half
    grows into a separate organism.
  • Cnidarians undergo budding where a new individual
    grows from and then breaks off of the parent
  • Echinoderms can be cut to form new individuals.
  • Insects- parthenogenesis (unfertilized egg

Sexual Reproduction
  • In sexual reproduction new individuals are
    produced by the fusion of haploid gametes to form
    a diploid zygote.
  • Sperm are male gametes, ova (ovum singular) are
    female gametes.
  • Meiosis produces cells that are genetically
    distinct from each other fertilization is the
    fusion of two such distinctive cells that
    produces a unique new combination of alleles,
    thus increasing variation on which natural
    selection can operate.

  • Sperm and eggs are sometimes produced by the same
    individual and sometimes produced by different
  • The sexes of vertebrates are separate but some
    vertebrates can change sex.

  • Sexual reproduction promotes variation because
    offspring inherit genes from two different
  • In addition, when an individual produces gametes,
    crossing-over and independent assortment mix
    genes from that individuals parents. Gametes are
    haploid they contain some genes from the
    individuals mother and some from the father.
  • Variation is advantageous to species in
    fluctuating environments.

Reproductive Cycles
  • Reproductive cycles in many vertebrates and
    invertebrates are related to changes in day
  • Day length is a reliable indicator of season for
    timing circannual events such as reproductive
    behavior and migration.
  • In many species, the pineal gland secretes
    melatonin in the dark. Increasing daylength
    (decreased melatonin levels) triggers
    reproductive behavior.

  • Sexually reproducing animals are either
  • Monoecious male and female in same organism
  • Dioecious male and female in different
  • Dioecious species are either sexually
  • Monomorphic (look the same)
  • dimorphic. (look different)

  • Even though monoecious organisms have both male
    and female reproductive systems they rarely
    fertilize their own eggs.
  • Either the two systems mature at different times
    or the events of sperm transfer and fertilization
    are separated.

  • They do have one advantage that dioecious
    organisms do not have. When dioecious organisms
    mate, only one parent produces new offspring.
    That's not the case with monoecious animals. When
    monoecious meet, they both can receive sperm from
    their partners and will later fertilize their own
    eggs with the sperm they received when they
  • The result is that when monoecious animals mate,
    both parents produce young. Monoecious organisms
    are often sessile or slow moving, and there is an
    advantage to having both animals produce young
    when there is a chance encounter.

  • The sexes of most sexually reproducing species
    differ in both primary sexual characteristics
    (sex organs) and secondary sexual characteristics
    associated with mating and bearing young.
  • Males are characterized by brighter colors and
    more elaborate structures such as horns. Bright
    colors may increase the attractiveness of males
    to females, while horns may serve as weapons for
    fighting with other males for control of a female.

Mono- and Dimorphic
  • Dimorphism is most pronounced in insects where
    the morphologies of the penis and vagina are
    precisely matched for each species, apparently
    preventing incorrect matings between closely
    related species.

Mechanisms of Sexual Reproduction
  • Fertilization plays an important role in
    reproduction--- can occur in two ways.
  • Internal
  • External

External Fertilization
  • During external fertilization, many gametes are
    released into the water by each sex at the same
    time and place. 
  • This type of fertilization requires water because
    animal sperm must swim to the eggs. Water also
    protects the gametes from drying out.
  • Species which have external fertilization are
    either aquatic or return to water for

Amphibian Eggs
Internal Fertilization
  • Internal fertilization is practiced by species
    that lay shelled eggs or have a period of
    internal embryonic development.
  • This type of fertilization enables animals to
    reproduce in a terrestrial environment because it
    enables sperm to swim to the egg and it prevents
    gametes from drying out.
  • The male often has a copulatory organ (a penis)
    for transferring sperm.
  • Males of some aquatic animals (ex sharks,
    skates, rays) have specialized pelvic fins which
    allow the sperm to be passed to the female.

Eggs and Birth
  • Animals can be grouped into those which
  • Give birth to living offspring and
  • Those which lay eggs that eventually hatch into
  • Those animals which give birth to live offspring
    are called live-bearing or viviparous.
  • Those animals which lay eggs are called
    egg-laying or oviparous. The difference is in the
    place where the offspring develops before it is

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Human Reproduction
  • Human reproduction employs internal
    fertilization, and depends on the integrated
    action of hormones, the nervous system, and the
    reproductive system.
  • Gonads are sex organs that produce gametes.
  • Male gonads are the testes, which produce sperm
    and male sex hormones.
  • Female gonads are the ovaries, which produce eggs
    (ova) and female sex hormones.

Male Reproductive System
  • Testes are suspended outside the abdominal cavity
    by the scrotum, a pouch of skin that keeps the
    testes close or far from the body at an optimal
    temperature for sperm development.
  • Seminiferous tubules are inside each testis, and
    are where sperm are produced by meiosis. About
    250 meters (850 feet) of tubules are packed into
    each testis.
  • Spermatocytes inside the tubules divide by
    meiosis to produce spermatids that in turn
    develop into mature sperm.

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  • Sperm production begins at puberty at continues
    throughout life, with several hundred million
    sperm being produced each day.
  • Once sperm form they move into the epididymis,
    where they mature and are stored.

Male Hormones
  • The anterior pituitary produces
    follicle-stimulating hormone (FSH) and
    luteinizing hormone (LH).
  • Action of LH is controlled by the
    gonadotropin-releasing hormone (GnRH).
  • LH stimulates cells in the seminiferous tubules
    to secrete testosterone, which has a role in
    sperm production and developing male secondary
    sex characteristics.
  • FSH acts on cells to help in sperm maturation.
    Negative feedback by testosterone controls the
    actions of GnRH.

  • Sperm pass through the vas deferens and connect
    to a short ejaculatory duct that connects to the
  • 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
  • The bulbourethral (Cowpers) gland secretes a
    mucus-like fluid that provides lubrication for
    intercourse. Sperm and secretions make up semen.

The Female Reproductive System
  • The female gonads, ovaries, are located within
    the lower abdominal cavity.
  • 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.
  • At birth each female carries a lifetime supply of
    developing oocytes, each of which is in Prophase
    I. A developing egg (secondary oocyte) is
    released each month from puberty until menopause,
    a total of 400-500 eggs.

The Ovarian Cycle
  • After puberty the ovary cycles between a
    follicular phase (maturing follicles) and a
    luteal phase (presence of the corpus luteum).
    These cyclic phases are interrupted only by
    pregnancy and continue until menopause, when
    reproductive capability ends. 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
  • Following ovulation the follicle forms a corpus
    luteum which synthesizes and prepares hormones to
    prepare the uterus for pregnancy.
  • 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 receives the penis during intercourse
    and serves as the birth canal.

External Genitals
  • The female external genitals are collectively
    known as the vulva.
  • The labia minora is a thin membrane of folded
    skin just outside the vaginal opening.
  • The labia majora cover and protect the genital

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Hormones and Cycles
  • The ovarian cycle is hormonally regulated in two
    phases. The follicle secretes estrogen before
    ovulation the corpus luteum secretes both
    estrogen and progesterone after ovulation.
  • Hormones from the hypothalamus and anterior
    pituitary control the ovarian cycle.
  • The ovarian cycle covers events in the ovary the
    menstrual cycle occurs in the uterus.

Menstrual Cycle
  • Menstrual cycles vary from between 15 and 31
  • 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.
  • FSH and LH are secreted on day 0, beginning both
    the menstrual cycle and the ovarian cycle. Both
    FSH and LH stimulate the maturation of a single
    follicle in one of the ovaries and the secretion
    of estrogen.

  • Rising levels of estrogen in the blood trigger
    secretion of LH, which stimulates follicle
    maturation and ovulation (day 14, or midcycle).
  • LH stimulates the remaining follicle cells to
    form the corpus luteum, which produces both
    estrogen and progesterone.
  • Estrogen and progesterone stimulate the
    development of the endometrium and preparation of
    the uterine inner lining for implantation of a
  • If pregnancy does not occur, the drop in FSH and
    LH cause the corpus luteum to disintegrate. The
    drop in hormones also causes the sloughing off of
    the inner lining of the uterus by a series of
    muscle contractions of the uterus.

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