Reproduction and Development

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CHAPTER 26

• Reproduction and Development
• Figures 26.1 26.2

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• During ejaculation, a man releases up to 500
  million sperm, only one of which may fertilize an
  egg

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• You have trillions of cells in your body, and
  they all arose from one original cell

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• An American woman is 4 times more likely to
  deliver triplets today than 25 years ago

• Even though a woman is born with up to half a
  million developing gametes, she will only use
  about 500 during her lifetime

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BIOLOGY AND SOCIETY RISE OF THE SUPERTWINS

• On November 19, 1997, news reports heralded the
  arrival of the Iowa septuplets

Figure 26.1
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• Other sets of multiple births soon followed

• What accounted for the sudden rash of multiple
  births?

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• All of these multiple births were by women who
  had taken fertility drugs because they couldnt
  become pregnant naturally

• Couples turn to fertility drugs to overcome their
  natural reproductive limitations

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UNIFYING CONCEPTS OF ANIMAL REPRODUCTION

• Reproduction is the creation of new individuals
  from existing ones

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Asexual Reproduction

• In asexual reproduction

• One parent produces genetically identical
  offspring

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• Binary fission

• Is the simplest type of asexual reproduction
• Involves a single parent cell splitting through
  mitosis into two genetically identical offspring
  cells

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• Some multicellular organisms reproduce by a
  similar means called fission, in which one
  organism splits into two or more individuals

Figure 26.2a
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• Fragmentation is the breaking of a parent body
  into several pieces

• Regeneration, which follows fragmentation, is the
  regrowth of a whole animal from the pieces

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• Budding

• Is the splitting off of new individuals from
  existing ones

Figure 26.2b
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• Asexual reproduction has a number of advantages

• It allows a species to perpetuate itself if its
  individual members are sessile or isolated from
  one another
• It allows organisms to multiply quickly

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• One potential disadvantage of asexual
  reproduction is that it produces genetically
  uniform populations

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Sexual Reproduction

• Sexual reproduction

• Involves the fusion of gametes (sperm and egg)
  from two parents
• Increases the genetic variability among offspring

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• Some animals can reproduce both sexually and
  asexually

Figure 26.3a
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• Some species are hermaphrodites with both male
  and female reproductive systems

Figure 26.3b
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• The mechanics of fertilization play an important
  part in sexual reproduction

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• Many organisms use external fertilization, in
  which parents discharge their gametes into the
  water, where fertilization occurs

Figure 26.3c
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• Other organisms use internal fertilization, which
  occurs within the females body

• Internal fertilization requires copulation, or
  sexual intercourse

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HUMAN REPRODUCTION

• Both sexes of humans have

• A pair of gonads, the organs that produce gametes
• Ducts to store and deliver the gametes
• Structures to facilitate copulation

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Female Reproductive Anatomy

• The ovaries

• Are the site of gamete production in human females

Ovaries
Oviduct
Follicles
Corpus luteum
Uterus
Wall of uterus
Endometrium (lining of uterus)
Cervix (neck of uterus)
Vagina
Figure 26.4
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• The ovaries contain follicles

• Each follicle consists of a single developing egg
  cell surrounded by layers of cells that nourish
  and protect it
• The follicles also produce estrogen, the female
  sex hormone

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• Ovulation

• Is the process by which an egg cell is ejected
  from the follicle

Figure 26.5
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• The egg enters the oviduct, which is a tube in
  which cilia sweep the egg toward the uterus

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• The uterus is the actual site of pregnancy

• The cervix, the narrow neck at the bottom of the
  uterus, opens into the vagina, or birth canal
• During copulation, the vagina serves as a
  repository for sperm

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Oviduct
Ovary

• Female reproductive anatomy

Rectum (digestive system)
Uterus
Bladder (excretory system)
Pubic bone
Urethra (excretory system)
Cervix
Vagina
Shaft
Glans
Clitoris
Prepuce
Labia minora
Labia majora
Vaginal opening
Figure 26.6
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Male Reproductive Anatomy

• The penis

• Contains erectile tissue

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• The testes

• Are the male gonads, enclosed in a sac called the
  scrotum
• Produce sperm

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• Semen
• Consists of this fluid and sperm

• Several glands
• Contribute to the formation of the fluid that
  carries, nourishes, and protects sperm

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• Male reproductive anatomy, side view

Bladder (excretory system)
Seminal vesicle
Pubic bone
Rectum (digestive system
Erectile tissue of penis
Vas deferens
Urethra
Prostate gland
Vas deferens
Glans of penis
Epididymis
Testis
Prepuce
Scrotum
Figure 26.7a
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• Male reproductive anatomy, front view

Seminal vesicle (behind bladder)
Bladder (excretory system)
Prostate gland
Urethra
Erectile tissue of penis
Vas deferens
Scrotum
Epididymis
Glans of penis
Testis
Figure 26.7b
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Gametogenesis

• Gametogenesis

• Is the production of gametes
• Human gametes
• Are haploid cells that develop by meiosis

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Oogenesis

• Oogenesis is the development of eggs within the
  ovaries

Diploid cell in embryo
Differentiation and onset of meiosis I
Ovary
Primary oocyte,
arrested in prophase of meiosis I present at
birth
Completion of meiosis I and onset of meiosis II
Corpus luteum
First polar body
Secondary oocyte,
Growing follicle
arrested at metaphase of meiosis II released
from ovary
Entry of sperm triggers completion of meiosis II
Mature follicle
Second polar body
Ovulation
Ruptured follicle
Ovum
(haploid)
Sperm
Figure 26.8
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Spermatogenesis

• Spermatogenesis

• Is the formation of sperm cells

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Epididymis
Penis
Testis
Scrotum
Diploid cell
Testis
Differentiation and onset of meiosis I
Seminiferous tubule
Primary spermatocyte
Cross section of seminiferous tubule
Meiosis I completed
Secondary spermatocyte
Meiosis II
Developing spermatids
Differentiation
Sperm cells
(haploid)
Center of seminiferous tubule
Figure 26.9