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Reproduction and Development Figures 26.1 – 26.2

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Presentation on theme: "Reproduction and Development Figures 26.1 – 26.2"— Presentation transcript:

1 Reproduction and Development Figures 26.1 – 26.2
CHAPTER 26 Reproduction and Development Figures 26.1 – 26.2

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

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

4 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

On November 19, 1997, news reports heralded the arrival of the Iowa septuplets Figure 26.1

6 Other sets of multiple births soon followed
What accounted for the sudden rash of multiple births?

7 All of these multiple births were by women who had taken fertility drugs because they couldn’t become pregnant naturally Couples turn to fertility drugs to overcome their natural reproductive limitations

Reproduction is the creation of new individuals from existing ones

9 Asexual Reproduction In asexual reproduction
One parent produces genetically identical offspring

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

11 Some multicellular organisms reproduce by a similar means called fission, in which one organism splits into two or more individuals Figure 26.2a

12 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

13 Budding Is the splitting off of new individuals from existing ones
Figure 26.2b

14 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

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

16 Sexual Reproduction Sexual reproduction
Involves the fusion of gametes (sperm and egg) from two parents Increases the genetic variability among offspring

17 Some animals can reproduce both sexually and asexually
Figure 26.3a

18 Some species are hermaphrodites with both male and female reproductive systems
Figure 26.3b

19 The mechanics of fertilization play an important part in sexual reproduction

20 Many organisms use external fertilization, in which parents discharge their gametes into the water, where fertilization occurs Figure 26.3c

21 Other organisms use internal fertilization, which occurs within the female’s body
Internal fertilization requires copulation, or sexual intercourse

22 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

23 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

24 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

25 Ovulation Is the process by which an egg cell is ejected from the follicle Figure 26.5

26 The egg enters the oviduct, which is a tube in which cilia sweep the egg toward the uterus

27 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

28 Female reproductive anatomy
Oviduct Female reproductive anatomy Ovary Rectum (digestive system) Uterus Bladder (excretory system) Pubic bone Cervix Urethra (excretory system) Vagina Shaft Glans Clitoris Prepuce Labia minora Labia majora Vaginal opening Figure 26.6

29 Male Reproductive Anatomy
The penis Contains erectile tissue

30 The testes Are the male gonads, enclosed in a sac called the scrotum
Produce sperm

31 Semen Consists of this fluid and sperm Several glands Contribute to the formation of the fluid that carries, nourishes, and protects sperm

32 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

33 Male reproductive anatomy, front view
Bladder (excretory system) Seminal vesicle (behind bladder) Prostate gland Urethra Erectile tissue of penis Vas deferens Scrotum Epididymis Testis Glans of penis Figure 26.7b

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

35 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 Ovum Ruptured follicle (haploid) Sperm Figure 26.8

36 Spermatogenesis Spermatogenesis Is the formation of sperm cells

37 Differentiation and onset of meiosis I Seminiferous tubule
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

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