1. Reproduction and Development
Chapter 26a
Reproduction and Development

2. Sex determination and differentiation
About this Chapter
Sex determination and differentiation
Gametogenesis and patterns of reproduction
Male reproductive development and physiology
Female reproductive development and physiology
Pregnancy and the birth process
The reproductive system during growth and aging

3. Gonads produce gametes and sex hormones
Sex Determination
Sexual dimorphism
Females and males are physically distinct
Gonads produce gametes and sex hormones
Male gonads = testes  sperm
Female gonads = ovaries  eggs
Sex hormones direct development of genitalia
Internal genitalia
External genitalia

4. Sex Determination Is Directed By Our Genome
Humans have 23 pairs of chromosomes
22 pairs of autosomes
X and Y = 1 pair of sex chromosomes
Nondisjunction
XXX superfemale
XXY Klinefelters
X0 Turners
XYY supermale
Figure 26-1

5. X and Y Chromosomes Determine Sex
Figure 26-2

6. Sexual Differentiation
Bipotential tissues have not yet differentiated
SRY protein directs development as a male
Gonadal medulla develops into testis
Testicular hormones direct further development
Absence of SRY protein leads to female development
Gonadal cortex develops into ovarian tissue
Mullerian ducts develop into female organs
Wolffian ducts degenerate

7. Sexual Differentiation
Table 26-1

8. Development of Internal Reproductive Organs
Müllerian duct
Wolffian duct
Bipotential gonad
Kidney
Cloacal opening
FEMALE
MALE
Bipotential stage: 6 week fetus The internal reproductive organs have the potential to develop into male or female structures 1
Gonadal cortex becomes ovary in the absence of SRY protein. 1
SRY protein in a male embryo directs the medulla of the bipotential gonad to develop into testis.
Testis 2
Absence of testosterone causes Wolffian duct to degenerate. 2
Anti-Müllerian hormone from testis causes the Müllerian ducts to disappear.
Wolffian duct
Müllerian duct
Uterus
10 WEEKS
Ovary 3
Testosterone from testis converts Wolffian duct into seminal vesicle, vas deferens, and epididymis. DHT controls prostate development. 3
Absence of anti- Müllerian hormone allows the Müllerian duct to become the fallopian tube, uterus, and upper part of the vagina.
Prostate
Seminal vesicle
Fallopian tube (from Müllerian duct)
Vas deferens
Uterus
Testis
AT BIRTH
Epididymis
Vagina
(a) DEVELOPMENT OF INTERNAL ORGANS
Figure 26-3a

9. Development of External Genitalia
Genital tubercle
homologous
Urethral groove
Labioscrotal swelling
Anus
Urethral fold
FEMALE
MALE
Bipotential stage (6 week fetus)
Clitoris
Penis
Urethral fold
Urethral fold
Labioscrotal swelling
Labioscrotal swelling
Anus
Anus 1
DHT causes development of male external genitalia.
10 WEEKS 1 1
In the absence of androgens, the external genitalia are feminized.
Glans penis
Labia majora
Clitoris
Shaft of penis
Urethral opening
Labia minora
Vaginal opening
Scrotum 2
The testes descend from the abdominal cavity into the scrotum.
Anus
Anus
AT BIRTH
(b) DEVELOPMENT OF EXTERNAL GENITALIA
Figure 26-3b

10. Control of Male Development
SRY gene directs male development
Figure 26-4

11. Control of Female Development
The SRY gene and protein are absent
Gonadal cortex develops into ovarian tissue
Mullerian ducts develop into female organs
Vagina
Uterus
Fallopian tubes
Wolffian ducts degenerate

12. Gametogenesis Differs in Males and Females
STAGE OF CELL DIVISION
MALE
Oögonium 1
MITOSIS
Spermatogonium
Germ cell proliferation
46 chromosomes per cell (only two shown here)
Embryo
Embryo
46 (diploid)
Oögonia
Spermatogonia
MEIOSIS 2
DNA replicates but no cell division.
Primary oocyte
Sister chromatids
Sister chromatids
Primary spermatocyte
46 chromosomes, duplicated 3
First meiotic division
First
polar body
Secondary oocyte (egg)
Primary gamete divides into two secondary gametes.
Reproductive adult
Secondary spermatocytes
(may not occur)
23 chromosomes, duplicated
Reproductive adult 4
Second meiotic division
Disintegrates
Spermatids
Egg released from ovary at ovulation.
Secondary gamete divides.
develop into
23 chromosomes (haploid)
Sperm 6
FERTILIZATION
One primary oocyte yields 1 egg.
One primary spermatocyte yields 4 sperm. 5
Second polar body disintegrates.
Unfertilized egg passes out of body.
Zygote
Figure 26-5

13. Mitosis: Germ Cell Proliferation
FEMALE
STAGE OF CELL DIVISION
MALE
Oögonium 1
MITOSIS
Spermatogonium
Germ cell proliferation
46 chromosomes per cell (only two shown here)
Embryo
Embryo
46 (diploid)
Oögonia
Spermatogonia
Reproductive adult
Reproductive adult
Figure 26-5, step 1

14. Meiosis: DNA Replicates
FEMALE
STAGE OF CELL DIVISION
MALE
Oögonium 1
MITOSIS
Spermatogonium
Germ cell proliferation
46 chromosomes per cell (only two shown here)
Embryo
Embryo
46 (diploid)
Oögonia
Spermatogonia
MEIOSIS 2
DNA replicates but no cell division.
Primary oocyte
Sister chromatids
Sister chromatids
Primary spermatocyte
46 chromosomes, duplicated
Polar bodies
Reproductive adult
Reproductive adult
Figure 26-5, steps 1–2

15. First Meiotic Division
FEMALE
STAGE OF CELL DIVISION
MALE
Oögonium 1
MITOSIS
Spermatogonium
Germ cell proliferation
46 chromosomes per cell (only two shown here)
Embryo
Embryo
46 (diploid)
Oögonia
Spermatogonia
MEIOSIS 2
DNA replicates but no cell division.
Primary oocyte
Sister chromatids
Sister chromatids
Primary spermatocyte
46 chromosomes, duplicated
Polar bodies 3
First meiotic division
First
polar body
Secondary oocyte (egg)
Primary gamete divides into two secondary gametes.
Reproductive adult
Secondary spermatocytes
23 chromosomes, duplicated
Reproductive adult
Figure 26-5, steps 1–3

16. Second Meiotic Division
FEMALE
STAGE OF CELL DIVISION
MALE
Oögonium 1
MITOSIS
Spermatogonium
Germ cell proliferation
46 chromosomes per cell (only two shown here)
Embryo
Embryo
46 (diploid)
Oögonia
Spermatogonia
MEIOSIS 2
DNA replicates but no cell division.
Primary oocyte
Sister chromatids
Sister chromatids
Primary spermatocyte
46 chromosomes, duplicated
Polar bodies 3
First meiotic division
First
polar body
Secondary oocyte (egg)
Primary gamete divides into two secondary gametes.
Reproductive adult
Secondary spermatocytes
(may not occur)
23 chromosomes, duplicated
Reproductive adult 4
Second meiotic division
Disintegrates
Spermatids
Egg released from ovary at ovulation.
Secondary gamete divides.
develop into
23 chromosomes (haploid)
Sperm
One primary spermatocyte yields 4 sperm.
Figure 26-5, steps 1–4

17. Ovulation Without Fertilization
FEMALE
STAGE OF CELL DIVISION
MALE
Oögonium 1
MITOSIS
Spermatogonium
Germ cell proliferation
46 chromosomes per cell (only two shown here)
Embryo
Embryo
46 (diploid)
Oögonia
Spermatogonia
MEIOSIS 2
DNA replicates but no cell division.
Primary oocyte
Sister chromatids
Sister chromatids
Primary spermatocyte
46 chromosomes, duplicated
Polar bodies 3
First meiotic division
First
polar body
Secondary oocyte (egg)
Primary gamete divides into two secondary gametes.
Reproductive adult
Secondary spermatocytes
(may not occur)
23 chromosomes, duplicated
Reproductive adult 4
Second meiotic division
Disintegrates
Spermatids
Egg released from ovary at ovulation.
Secondary gamete divides.
develop into
23 chromosomes (haploid)
Sperm
One primary oocyte yields 1 egg.
One primary spermatocyte yields 4 sperm. 5
Unfertilized egg passes out of body.
Figure 26-5, steps 1–5

18. Ovulation with Fertilization Is Followed by Final Step of Meiosis
FEMALE
STAGE OF CELL DIVISION
MALE
Oögonium 1
MITOSIS
Spermatogonium
Germ cell proliferation
46 chromosomes per cell (only two shown here)
Embryo
Embryo
46 (diploid)
Oögonia
Spermatogonia
MEIOSIS 2
DNA replicates but no cell division.
Primary oocyte
Sister chromatids
Sister chromatids
Primary spermatocyte
46 chromosomes, duplicated
Polar bodies 3
First meiotic division
First
polar body
Secondary oocyte (egg)
Primary gamete divides into two secondary gametes.
Reproductive adult
Secondary spermatocytes
(may not occur)
23 chromosomes, duplicated
Reproductive adult 4
Second meiotic division
Disintegrates
Spermatids
Egg released from ovary at ovulation.
Secondary gamete divides.
develop into
23 chromosomes (haploid)
Sperm 6
FERTILIZATION
One primary oocyte yields 1 egg.
One primary spermatocyte yields 4 sperm. 5
Second polar body disintegrates.
Unfertilized egg passes out of body.
Zygote
Figure 26-5, steps 1–6

19. Steroid Synthesis Pathways
Steroid hormones are similar to each other
Production of sex steroids differs between men and women
Ovary
Estrogen and progesterone
Testis
Testosterone and dihydrotestosterone (DHT)
Adrenal gland secretes small amounts of sex steroids

20. Synthesis Pathways for Steroid Hormones
Cholesterol
Progesterone *
Dihydro- testosterone (DHT)
Testosterone
aromatase
Corticosterone
Cortisol
Estradiol
KEY *
5-reductase
Aldosterone
Intermediate steps
Figure 26-6

21. Hormonal Regulation of Reproduction
Anterior pituitary
Luteinizing hormone (LH)
Follicle stimulating hormone (FSH)
Gonads produce steroid and peptide hormones
Gonads are the main source of sex steroid

22. General Pattern of Hormonal Control of Reproduction
Internal and environmental stimuli
CNS
GnRH
Hypothalamus
Short-loop negative feedback
KEY
Stimulus
Anterior pituitary
Integrating center
Efferent pathway
Effector
Long-loop feedback may be negative or positive LH
FSH
Tissue response
Gonads (ovaries or testes)
Females only
Endocrine cells
Gamete production
Steroid and peptide hormones
Figure 26-7

23. Consequences of Feedback
Table 26-2