Chapter 26a
Reproduction
and Development
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
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
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
X and Y Chromosomes Determine Sex
Figure 26-2
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
Sexual Differentiation
Table 26-1
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.
Testis
2 Absence of testosterone
causes Wolffian duct
to degenerate.
Wolffian
duct
Müllerian duct
1 SRY protein in a male
embryo directs the
medulla of the
bipotential gonad
to develop into testis.
2 Anti-Müllerian
hormone from testis
causes the Müllerian
ducts to disappear.
Uterus
10 WEEKS
Ovary
3 Absence of antiMüllerian 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)
Uterus
Vagina
Vas deferens
Testis
AT BIRTH
3 Testosterone from
testis converts Wolffian
duct into seminal
vesicle, vas deferens,
and epididymis. DHT
controls prostate
development.
Epididymis
(a) DEVELOPMENT OF INTERNAL ORGANS
Figure 26-3a
Development of External Genitalia
Genital tubercle
homologous
Urethral groove
Labioscrotal swelling
Urethral fold
Anus
FEMALE
MALE
Bipotential stage
(6 week fetus)
Clitoris
Penis
Urethral fold
Urethral fold
Labioscrotal
swelling
Labioscrotal
swelling
Anus
Anus
10 WEEKS
1 In the absence
of androgens,
the external genitalia
are feminized.
1 DHT causes
development
of male external
genitalia.
Glans penis
Labia
majora
Clitoris
Urethral opening
Labia
minora
Vaginal opening
Anus
Shaft of penis
Scrotum
Anus
AT BIRTH
2 The testes descend
from the abdominal
cavity into the
scrotum.
(b) DEVELOPMENT OF EXTERNAL GENITALIA
Figure 26-3b
Control of Male Development
• SRY gene directs male
development
Figure 26-4
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
Gametogenesis Differs in Males and Females
FEMALE
Oögonium
MALE
1 MITOSIS
Germ cell proliferation
Spermatogonium
Embryo
46 chromosomes
per cell (only two
shown here)
46
(diploid)
Oögonia
Spermatogonia
MEIOSIS
2
Primary
oocyte
Sister
chromatids
(may not
occur)
Disintegrates
Egg released
from ovary at
ovulation.
3 First meiotic
division
Primary gamete divides
into two secondary gametes.
23 chromosomes,
duplicated
4
Secondary gamete divides.
23 chromosomes
(haploid)
6
One primary oocyte
yields 1 egg.
Second meiotic
division
FERTILIZATION
Primary
spermatocyte
Sister
chromatids
46 chromosomes,
duplicated
Reproductive adult
Secondary
oocyte
(egg)
DNA replicates
but no cell division.
Reproductive adult
First
polar
body
Embryo
STAGE OF CELL DIVISION
Secondary
spermatocytes
Spermatids
develop into
Sperm
One primary spermatocyte
yields 4 sperm.
5
Second
polar body
disintegrates.
Unfertilized egg
passes out of body.
Zygote
Figure 26-5
Mitosis: Germ Cell Proliferation
FEMALE
Oögonium
MALE
1 MITOSIS
Germ cell proliferation
Spermatogonium
Embryo
46 chromosomes
per cell (only two
shown here)
46
(diploid)
Spermatogonia
Reproductive adult
Reproductive adult
Oögonia
Embryo
STAGE OF CELL DIVISION
Figure 26-5, step 1
Meiosis: DNA Replicates
FEMALE
Oögonium
MALE
1 MITOSIS
Germ cell proliferation
Spermatogonium
Embryo
46 chromosomes
per cell (only two
shown here)
46
(diploid)
Oögonia
Spermatogonia
MEIOSIS
2
Primary
oocyte
Embryo
STAGE OF CELL DIVISION
Sister
chromatids
DNA replicates
but no cell division.
Sister
chromatids
46 chromosomes,
duplicated
Reproductive adult
Reproductive adult
Polar
bodies
Primary
spermatocyte
Figure 26-5, steps 1–2
First Meiotic Division
FEMALE
Oögonium
MALE
1 MITOSIS
Germ cell proliferation
Spermatogonium
Embryo
46 chromosomes
per cell (only two
shown here)
46
(diploid)
Oögonia
2
Sister
chromatids
Sister
chromatids
46 chromosomes,
duplicated
Reproductive adult
Secondary
oocyte
(egg)
DNA replicates
but no cell division.
3 First meiotic
division
Primary gamete divides
into two secondary gametes.
23 chromosomes,
duplicated
Reproductive adult
First
polar
body
Spermatogonia
MEIOSIS
Primary
oocyte
Polar
bodies
Embryo
STAGE OF CELL DIVISION
Primary
spermatocyte
Secondary
spermatocytes
Figure 26-5, steps 1–3
Second Meiotic Division
FEMALE
Oögonium
MALE
1 MITOSIS
Germ cell proliferation
Spermatogonium
Embryo
46 chromosomes
per cell (only two
shown here)
46
(diploid)
Oögonia
2
Sister
chromatids
(may not
occur)
Disintegrates
Egg released
from ovary at
ovulation.
3 First meiotic
division
Primary gamete divides
into two secondary gametes.
23 chromosomes,
duplicated
4
Second meiotic
division
Secondary gamete divides.
23 chromosomes
(haploid)
Primary
spermatocyte
Sister
chromatids
46 chromosomes,
duplicated
Reproductive adult
Secondary
oocyte
(egg)
DNA replicates
but no cell division.
Reproductive adult
First
polar
body
Spermatogonia
MEIOSIS
Primary
oocyte
Polar
bodies
Embryo
STAGE OF CELL DIVISION
Secondary
spermatocytes
Spermatids
develop into
Sperm
One primary spermatocyte
yields 4 sperm.
Figure 26-5, steps 1–4
Ovulation Without Fertilization
FEMALE
Oögonium
MALE
1 MITOSIS
Germ cell proliferation
Spermatogonium
Embryo
46 chromosomes
per cell (only two
shown here)
46
(diploid)
Oögonia
2
Sister
chromatids
(may not
occur)
Disintegrates
Egg released
from ovary at
ovulation.
One primary oocyte
yields 1 egg.
3 First meiotic
division
Primary gamete divides
into two secondary gametes.
23 chromosomes,
duplicated
4
Second meiotic
division
Secondary gamete divides.
23 chromosomes
(haploid)
Primary
spermatocyte
Sister
chromatids
46 chromosomes,
duplicated
Reproductive adult
Secondary
oocyte
(egg)
DNA replicates
but no cell division.
Reproductive adult
First
polar
body
Spermatogonia
MEIOSIS
Primary
oocyte
Polar
bodies
Embryo
STAGE OF CELL DIVISION
Secondary
spermatocytes
Spermatids
develop into
Sperm
One primary spermatocyte
yields 4 sperm.
5
Unfertilized egg
passes out of body.
Figure 26-5, steps 1–5
Ovulation with Fertilization Is Followed by Final Step
of Meiosis
FEMALE
Oögonium
MALE
1 MITOSIS
Germ cell proliferation
Spermatogonium
Embryo
46 chromosomes
per cell (only two
shown here)
46
(diploid)
Oögonia
2
Sister
chromatids
(may not
occur)
Disintegrates
Egg released
from ovary at
ovulation.
3 First meiotic
division
Primary gamete divides
into two secondary gametes.
23 chromosomes,
duplicated
4
Secondary gamete divides.
23 chromosomes
(haploid)
6
One primary oocyte
yields 1 egg.
Second meiotic
division
FERTILIZATION
Primary
spermatocyte
Sister
chromatids
46 chromosomes,
duplicated
Reproductive adult
Secondary
oocyte
(egg)
DNA replicates
but no cell division.
Reproductive adult
First
polar
body
Spermatogonia
MEIOSIS
Primary
oocyte
Polar
bodies
Embryo
STAGE OF CELL DIVISION
Secondary
spermatocytes
Spermatids
develop into
Sperm
One primary spermatocyte
yields 4 sperm.
5
Second
polar body
disintegrates.
Unfertilized egg
passes out of body.
Zygote
Figure 26-5, steps 1–6
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
Synthesis Pathways for Steroid Hormones
Cholesterol
Progesterone
*
Testosterone
Dihydrotestosterone
(DHT)
aromatase
Corticosterone
Cortisol
Estradiol
KEY
*
Aldosterone
5-reductase
Intermediate steps
Figure 26-6
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
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
Tissue response
FSH
Gonads
(ovaries or testes)
Endocrine
cells
Steroid and
peptide hormones
Gamete
production
Figure 26-7
Consequences of Feedback
Table 26-2