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Chapter 46: Animal Reproduction

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1 Chapter 46: Animal Reproduction
Sections 46.1 and 46.2 Erin Foeri Period 2A

2 Concept 46.1- Both asexual and sexual reproduction occur in the animal kingdom
Sexual reproduction- fusion of egg and sperm (haploid) to form zygote (diploid) Asexual reproduction- offspring created without fusion of gametes

3 Mechanisms of Asexual Reproduction (Invertebrates)
Fission Budding Fragmentation and Regeneration Parthenogenesis Fission- one parent organism divides into two offspring of equal size Budding- new organism derived from overgrowth of original Fragmentation and Regeneration- parts of organism cut off, these parts regenerate into new organisms Parthenogenesis- egg develops without being fertilized; can be haploid or diploid

4 Advantages of Sexual vs. Asexual
Sexual- unique combinations, varied genotypes (rid population of harmful genotypes quickly, adaption sped up) Asexual- successful genotypes efficiently and rapidly

5 Sexual Reproductive Cycles
Ovulation- release of mature eggs at midpoint of each cycle Enhance chances of offspring survival Controlled by change of season/environmental cues and hormones Purpose of reproductive cycles- animals conserve energy sources and only reproduce when environmental conditions are in favor Environmental cues such as day length, seasonal temperature, rainfall, and lunar cycles influence sex cycles

6 Variations in Patterns of Sexual Reproduction
Solution when difficult to find mates: Hermaphroditism- organism has both male and female reproductive systems Some can self-fertilize, two hermaphrodites can mate Hermaphrodites can mate with each other, and capable of self-fertilization

7 Parthenogenesis- Sex Reversals
Complex form of parthenogenesis; both of these lizards are female- one female’s estradiol hormone level is high before ovulation; after ovulation, estradiol drops and progesterone (male hormone) increases- behaves like a male Benefit- when actual sexual behaviors are simulated (when lizard is mounted), more eggs are likely to be released than parthenogenetic lizards that ovulate in isolation **Found in some fish, amphibians, and reptiles

8 Concept Fertilization depends on mechanisms that bring together sperm and eggs of the same species External fertilization- eggs fertilized in environment Internal fertilization- sperm deposited in or near female reproductive tract Pheremones- chemical signals released by mating animals External fertilization- female releases egg into environment, male fertilizes it Internal fertilization- adaption that increases efficiency of sperm reaching egg, even in dry environments Pheremones- can change the physiology and behavior of mating animal; always used no matter which method of fertilization

9 Ensuring the Survival of Offspring
Internal vs. External More gametes= lower survival rate Spawning- release of gametes in mass numbers Less protection- gelatinous coat, no internal membrane Greater protection of embryo Certain adaptions that protect from water loss/other damage Egg-laying animals- shells are calcium and protein rich

10 Gamete Production and Delivery
Simple systems No gonads (gamete-producing organs) Gametes develop from undifferentiated cells Elaborate systems Tubes and glands to carry, nourish, and protect gametes

11 Insect Reproductive Anatomy

12 parthenogenesis in aphids
Animal homosexuality Gender change in fish

13 Video: Hydra Releasing Sperm
© 2011 Pearson Education, Inc.

14 Initiated external fertilization.
Figure 46.6 External fertilization.

15 External fertilization Internal fertilization Pros Cons
© 2011 Pearson Education, Inc. 15

16 Parental care: Surinam toad mom mouth-brooding cichlids
Figure 46.7 Parental care in an invertebrate.

17 At what are we looking? © 2011 Pearson Education, Inc. 17

18 A cloaca of a red-tailed hawk
© 2011 Pearson Education, Inc.

19 Gender-specific reproductive anatomy
Accessory gland Ovary Testis Oviduct Spermatheca Vas deferens Ejaculatory duct Seminal vesicle Uterus Accessory gland Penis and claspers Vulva Figure 46.8 Insect reproductive anatomy. (a) Male fruit fly (b) Female fruit fly

20 Animation: Female Reproductive Anatomy Right-click slide / select “Play”
© 2011 Pearson Education, Inc.

21 Major vestibular (Bartholin’s) gland Labia minora Labia majora
Figure 46.10 Oviduct Ovary Uterus (Urinary bladder) (Pubic bone) (Rectum) Urethra Cervix Body Vagina Glans Clitoris Prepuce Major vestibular (Bartholin’s) gland Labia minora Labia majora Vaginal opening Oviduct Ovaries Figure Reproductive anatomy of the human female. Follicles Corpus luteum Uterus Uterine wall Endometrium Cervix Vagina

22 Mammary Glands The mammary glands are not part of the reproductive system but are important to mammalian reproduction Within the glands, small sacs of epithelial tissue secrete milk animation © 2011 Pearson Education, Inc.

23 Male Reproductive Anatomy
The male’s external reproductive organs are the scrotum and penis Internal organs are the gonads, which produce sperm and hormones, and accessory glands Most mammals have a baculum (penile bone) Raccoon’s baculum  © 2011 Pearson Education, Inc.

24 Animation: Male Reproductive Anatomy Right-click slide / select “Play”
© 2011 Pearson Education, Inc.

25 Seminal vesicle (behind bladder)
Figure 46.11 Seminal vesicle (behind bladder) (Urinary bladder) Prostate gland Bulbourethral gland Urethra Erectile tissue of penis Scrotum Vas deferens Epididymis Testis (Urinary bladder) Seminal vesicle (Urinary duct) Figure Reproductive anatomy of the human male. (Rectum) (Pubic bone) Vas deferens Erectile tissue Ejaculatory duct Prostate gland Urethra Penis Bulbourethral gland Vas deferens Glans Epididymis Testis Prepuce Scrotum

26 Accessory Glands Semen is composed of sperm plus secretions from three sets of accessory glands The two seminal vesicles contribute about 60% of the total volume of semen The prostate gland secretes its products directly into the urethra through several small ducts The bulbourethral glands secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra © 2011 Pearson Education, Inc.

27 Gametogenesis Spermatogenesis, the development of sperm, is continuous and prolific (millions of sperm are produced per day; each sperm takes about 7 weeks to develop Oogenesis, the development of a mature egg, is a prolonged process Immature eggs form in the female embryo but do not complete their development until years or decades later © 2011 Pearson Education, Inc.

28 Spermatogenesis differs from oogenesis in three ways
All four products of meiosis develop into sperm while only one of the four becomes an egg Spermatogenesis occurs throughout adolescence and adulthood Sperm are produced continuously without the prolonged interruptions in oogenesis © 2011 Pearson Education, Inc.


30 Cross section of seminiferous tubule Secondary spermatocyte
Figure 46.12aa Epididymis Seminiferous tubule Sertoli cell nucleus Spermato- gonium Primary spermatocyte Testis Cross section of seminiferous tubule Secondary spermatocyte Spermatids (two stages) Figure Exploring: Human Gametogenesis Sperm cell Lumen of seminiferous tubule

31 Primordial germ cell in embryo Mitotic divisions
Figure 46.12ab Primordial germ cell in embryo Mitotic divisions Spermatogonial stem cell 2n Mitotic divisions Spermatogonium 2n Mitotic divisions Primary spermatocyte 2n Meiosis I Secondary spermatocyte n n Meiosis II Figure Exploring: Human Gametogenesis Early spermatid n n n n Differentiation (Sertoli cells provide nutrients) Sperm cell n n n n

32 Neck Tail Midpiece Head Plasma membrane Acrosome Nucleus Mitochondria
Figure 46.12ac Neck Tail Midpiece Head Plasma membrane Acrosome Nucleus Figure Exploring: Human Gametogenesis Mitochondria

33 Figure 46.12 Exploring: Human Gametogenesis
Figure 46.12b Primary oocyte within follicle Ovary Growing follicle Primordial germ cell In embryo Mitotic divisions 2n Oogonium Mitotic divisions Primary oocyte (present at birth), arrested in prophase of meiosis I Mature follicle 2n Ruptured follicle Completion of meiosis I and onset of meiosis II First polar body n n Secondary oocyte, arrested at metaphase of meiosis II Ovulated secondary oocyte Figure Exploring: Human Gametogenesis Ovulation, sperm entry Completion of meiosis II Second polar body Corpus luteum n Fertilized egg n Degenerating corpus luteum

34 46.4: The interplay of tropic and sex hormones regulates mammalian reproduction
Gonadotropin-releasing hormone (GnRH) secreted by hypothalamus -Follicle stimulating hormone (FSH) -Luteinizing hormone (LH) Steroid Hormones: Males: Androgens → Testosterone Sex characteristics, deeper voice, facial hair Females: Estrogens → Estradiol and progesterone Breast and pubic hair development, influences sexual behavior Regulate gametogenesis by... -Targeting tissues in gonads -Regulating sex hormone production

35 Hormonal Control of Female Reproductive Cycles
Secretion of hormones in females is cyclic Menstrual / Uterine cycle -Changes in the uterus -Shedding of blood and endometrium through cervix and vagina Ovarian cycle -Changes in the ovaries Ovulation -Endometrium thickens w/ blood vessels -Preparation for implantation

36 The reproductive cycle of a human female

37 The Ovarian Cycle Hormone release signals follicle growth
Estradiol increases in follicular phase Second oocyte released at ovulation Follicular tissue → corpus luteum The corpus luteum disintegrates due to low gonadotropin levels Ovarian steroid hormones decrease & negative-feedback ends

38 Uterine (Menstrual) Cycle
Ovarian hormones stimulate uterus to prepare for embryo Proliferative phase coordinated to follicular phase (endometrial thickening) Secretory phase coordinates with luteal phase Menstrual flow phase (shedding of endometrium) coordinates with growth of ovarian follicles Endometriosis: swelling of uterine lining cells that have migrated to an ectopic location

39 Menopause After 500 cycles ovulation and menstruation ceases
Decline in estradiol production Unusual phenomenon

40 Menstrual vs. Estrous Cycles
Endometrium thickens before ovulation in all female mammals Uterus reabsorbs it if an embryo is not implanted Estrus period around ovulation is the female mating time (heat) Length and frequency varies among animals 1/yr 5 days

41 Hormonal Control of the Male Reproductive System
Sertoli cells nourish developing sperm Leydig cells secrete testosterone -Promote spermatogenesis Testosterone regulates FSH, LH, and GnRH levels Inhibin reduces FSH secretion

42 Human Sexual Response Testosterone, prolactin, and oxytocin
Physiological responses in both sexes: vasocongestion and myotonia Four Phases: 1. Excitement 2. Plateau 3. Orgasm 4. Resolution Inner vagina expands & depression for sperm forms Breathing and heart rate increases Contractions of reproductive structures Semen released & ejaculated Organs return to normal state Muscles relax Males enter refractory period Prepares for coitus → erection, enlargement, lubrication and myotonia

43 46.5 In placental mammals, an embryo develops fully within the mother’s uterus
Egg develops into an embryo in reproduction

44 Conception, Embryonic Development, and Birth
Conception in the oviduct is when sperm fuses with an egg Zygote forms and begins dividing Division by mitosis, with cleavage, gives rise to blastocyst Embryo implants into endometrium and releases human chorionic gonadotropin (hCG) to prevent menstruation Ectopic pregnancy occurs when a fertilized egg develops in fallopian tube


46 First Trimester Human gestation divided into three trimesters, each with three months Most radical change for mother and embryo in first tri. Endometrium grows over the blastocyst during implantation Embryo obtains nutrients from endometrium in first 2-4 weeks

47 Trophoblast grows outward and forms placenta with the endometrium
The umbilical cord carries blood to the placenta and returns via umbilical vein Identical twins develop if the embryo splits during the first month Fraternal twins develop if two eggs are fertilized Body organs are developed in the first trimester (organogenesis) By 8 weeks, embryo is called a fetus

48 -Growth of placenta and uterus
Changes in the mother: -Mucus plug -Growth of placenta and uterus -Cessation of ovulation and menstrual cycle -Breast enlargement -Nausea is common Changes in embryo:

49 Second & Third Trimester
-Uterus grows and pregnancy is apparent -Fetus is very active -hCG declines; corpus luteum deteriorates; and the placenta takes over the production of progesterone to maintain the pregnancy -Fetus fills the space between embryonic membranes -Labor is induced by hormones produced by the fetus -Regulators and hormones induce and regulate further contractions

50 Three stages of labor: 1. Thinning and dilation of the cervix 2. Expulsion of the baby 3. Delivery of the placenta Mammals lactate and newborns suckle their mother’s milk

51 Maternal Immune Tolerance of the Embryo and Fetus
Embryo is foreign to mother due to paternal genes on its surface Regulation of immune process altered by pregnancy Acceptance of offspring may be due to the suppression of the immune response in the uterus

52 Contraception and Abortion
Contraception can be categorized in three ways: Preventing release of eggs and sperm Keeping eggs and sperm apart Preventing implantation of an embryo

53 Fertilization can be prevented by abstinence or barriers
Rhythm method is temporary abstinence when conception is most likely Hormone based contraceptives mimic negative feedback in the ovarian cycle and inhibits ovulation and follicle development Abortion is the termination of a pregnancy Spontaneous abortion (miscarriage) occurs in ⅓ of pregnancies

54 Modern Reproductive Technologies
Amniotic fluids or fetal cells can be obtained for genetic analysis Amniocentesis and chorionic villus Ultrasounds can show fetal condition Genetic testing of the fetus brings rise to many ethical arguments

55 Infertility Treatment:
Assisted reproductive technologies In vitro fertilization (IVF) Mixed in culture dishes, then returned to embryo Intracytoplasmic sperm injection (ICSI) Sperm injected with needle into oocyte

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