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Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Chapter 7
Development and
Sex Determination
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Sexual Differentiation in Humans
• Begins in the 7th week of development
• Is influenced by genetic and environmental factors
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Human Reproductive System
– Zygote fertilized egg (diploid)– Gametes unfertilized germ cells – Sperm male gamete (haploid)– Oocyte female gamete (haploid)– Gonads organs where gametes and
sex hormones are produced (testes and ovaries)
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Male Reproductive System
Fig. 7.1
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Spermatogenesis
Fig. 7.2
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Spermatogenesis
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Spermatogenesis
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning Seminiferous tubule filled with sperm. SEM X335.
Credit: © Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited 99917
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Human sperm. TEM.
Credit: © Dr. David Phillips/Visuals Unlimited 99895
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning Human sperm. TEM.Credit: © Dr. David Phillips/Visuals Unlimited
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Female Reproductive System
Fig. 7.3
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-4, p.155
Ovary
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-4, p.155
Primary oocyte, not yetreleased from meiosis I. Acell layer is forming aroundit. A follicle consists of thecell layer and the oocyte. Ovary
Primordialfollicle
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-4, p.155
Primary oocyte, not yetreleased from meiosis I. Acell layer is forming aroundit. A follicle consists of thecell layer and the oocyte.
A transparent andsomewhat elastic layer,the zona pellucida,starts forming aroundthe primary oocyte. Ovary
Primordialfollicle
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-4, p.155
Primary oocyte, not yetreleased from meiosis I. Acell layer is forming aroundit. A follicle consists of thecell layer and the oocyte.
A transparent andsomewhat elastic layer,the zona pellucida,starts forming aroundthe primary oocyte. Ovary
Primordialfollicle
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-4, p.155
Primary oocyte, not yetreleased from meiosis I. Acell layer is forming aroundit. A follicle consists of thecell layer and the oocyte.
A transparent andsomewhat elastic layer,the zona pellucida,starts forming aroundthe primary oocyte.
Mature follicle.Meiosis I is over.The secondaryoocyte and firstpolar body arenow formed.
Secondary oocyte
First polar body
Ovary
Primordialfollicle
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-4, p.155
Primary oocyte, not yetreleased from meiosis I. Acell layer is forming aroundit. A follicle consists of thecell layer and the oocyte.
A transparent andsomewhat elastic layer,the zona pellucida,starts forming aroundthe primary oocyte.
Mature follicle.Meiosis I is over.The secondaryoocyte and firstpolar body arenow formed.
Secondary oocyte
First polar body
Ovulation. The mature follicle ruptures, releasingthe secondary oocyte and first polar body.
Ovary
Primordialfollicle
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-4, p.155
Primary oocyte, not yetreleased from meiosis I. Acell layer is forming aroundit. A follicle consists of thecell layer and the oocyte.
A transparent andsomewhat elastic layer,the zona pellucida,starts forming aroundthe primary oocyte.
Mature follicle.Meiosis I is over.The secondaryoocyte and firstpolar body arenow formed.
Secondary oocyte
First polar body
Ovulation. The mature follicle ruptures, releasingthe secondary oocyte and first polar body.
A corpusluteum formsfrom remnantsof the rupturedfollicle.
Ovary
Primordialfollicle
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-4, p.155
Primary oocyte, not yetreleased from meiosis I. Acell layer is forming aroundit. A follicle consists of thecell layer and the oocyte.
A transparent andsomewhat elastic layer,the zona pellucida,starts forming aroundthe primary oocyte.
Mature follicle.Meiosis I is over.The secondaryoocyte and firstpolar body arenow formed.
The corpusluteum breaksdown whenthe womandoesn’t getpregnant.
Secondary oocyte
First polar body
Ovulation. The mature follicle ruptures, releasingthe secondary oocyte and first polar body.
A corpusluteum formsfrom remnantsof the rupturedfollicle.
Ovary
Primordialfollicle
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning Credit: © Gary Martin/Visuals Unlimited
Ovulation
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Timing of Meiosis and Spermatogenesis
• Large numbers of sperm are in constant production
• Four functional, equally-sized gametes per primary spermatocyte
• Over a lifetime a male produces billions of sperm
• Spermatogenesis takes approximately 48 days
• Each ejaculation can contain 200-400m sperm
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Timing of Meiosis and Oogenesis• Unequal cytoplasmic division and produces 1 large
functional gamete and 3 nonfunctional polar bodies• Primary oocytes are produced prior to birth and are
held in meiosis I • After puberty, one oocyte completes meiosis I each
monthly cycle, starts meiosis II and arrests at metaphase of meiosis II
• If fertilization occurs, it completes meiosis II• Time for complete cycle is 12–50 years• Release about 450 oocytes in a lifetime
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
1 spermatogonium 4 mature sperm
1 oogonium 1 oocyte + 3 polar bodies
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fertilization to Implantation
• Fertilization is the fusion of two gametes to produce a zygote
• Zygote is moved by cilia in the lining of the oviduct to the uterus
• The zygote divides by mitosis• Forms a early embryonic stage, the
blastocyst
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Sperm enter vagina
Ovulation
Vagina
Opening of cervix
Uterus
Ovary
OviductFertilization
Stepped ArtFig. 7-5b, p.157
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Sperm enter vaginaZona
pellucida
Follicle cell
Ovulation
Vagina
Opening of cervix
Uterus
Ovary
OviductFertilization
Egg nucleus
Stepped ArtFig. 7-5b, p.157
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Sperm enter vaginaZona
pellucida
Follicle cell
Ovulation
Vagina
Opening of cervix
Uterus
Ovary
OviductFertilization
Egg nucleus
Stepped ArtFig. 7-5b, p.157
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Sperm enter vagina
Nuclei fuseFusion of sperm nucleus with egg nucleus
Zona pellucida
Follicle cell
Ovulation
Vagina
Opening of cervix
Uterus
Ovary
OviductFertilization
Egg nucleus
Stepped ArtFig. 7-5b, p.157
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Sperm enter vagina
Nuclei fuseFusion of sperm nucleus with egg nucleus
Zona pellucida
Follicle cell
Ovulation
Vagina
Opening of cervix
Uterus
Ovary
OviductFertilization
Egg nucleus
Stepped ArtFig. 7-5b, p.157
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning Sperm entering the oviduct. SEM X500.
Credit: © Dr. David Phillips/Visuals Unlimited 350626
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning Fertilization. SEM X4700.
Credit: © Dr. David Phillips/Visuals Unlimited 167105
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Cleavage and gastrulation (Xenopus embryo)
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Blastocyst
• Mass of approximately 100 cells• It has two parts
– Inner cell mass gives rise to the embryo
– Trophoblast gives rise to surrounding membranes
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Implantation
• The trophoblast attaches to the endometrium of the uterus
• Villi (finger like projections) grow into the endometrium and anchor the embryo
• After approximately 12 days, the trophoblast has formed the chorion
• Chorion secretes human chorionic gonadotropin (hCG) which maintains the uterine lining (pregnancy test)
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Placenta
• Highly vascular• Formed from the chorionic villi• Allows oxygen, wastes, nutrients, and other
molecules to be exchanged between the mother and child
• Membranes that connect the embryo to the placenta form the umbilical cord
• Source of stem cells
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6a-e, p.159Stepped Art
Endometrium
Fertilization
Implantation
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6a-e, p.159Stepped Art
Endometrium
Fertilization
Implantation
DAYS 1-2
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6a-e, p.159Stepped Art
Endometrium
Fertilization
Implantation
DAYS 1-2 DAY 3
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6a-e, p.159Stepped Art
Endometrium
Fertilization
Implantation
DAYS 1-2 DAY 3 DAY 4
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6a-e, p.159Stepped Art
Endometrium
Fertilization
Implantation
DAYS 1-2 DAY 3 DAY 4 DAY 5
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6a-e, p.159Stepped Art
Endometrium
Fertilization
Implantation
Inner cell mass
DAYS 1-2 DAY 3 DAY 4 DAY 5 DAY 5
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6a-e, p.159Stepped Art
Trophoblast (surface layer of
cells of the blastocyst)
Uterine cavity
Endometrium
Inner cell
mass
Fertilization
Implantation
Inner cell mass
Endometrium
blastocoel
DAYS 1-2 DAY 3 DAY 4 DAY 5 DAY 5 DAYS 6-7
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6f-h, p.159
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6f-h, p.159
DAYS 10–11
Start ofyolk sac
Start ofembryonic disk
Start ofamniotic cavity
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6f-h, p.159
DAYS 10–11 DAY 12
Start ofchorionic cavity
Start ofyolk sac
Start ofembryonic disk
Start ofamniotic cavity
Blood-filled spaces
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6f-h, p.159
DAYS 10–11 DAY 12 DAY 14
Connectivetissue
Amnioticcavity
ChorionChorionic villi
Chorionic cavity
Start ofchorionic cavity
Start ofyolk sac
Start ofembryonic disk
Start ofamniotic cavity
Yolk sac
Blood-filled spaces
Stepped Art
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7a1, p.160
Connecting stalk
WEEKS 5–6WEEK 4Yolk sac
Embryo
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7a2, p.160
Forebrain
Future lens
Pharyngealarches
Developing heart
Upper limb bud
Somites
Neural tubeforming
Lower limbbud
Tail
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7b, p.160
Umbilical cord formationbetween weeks 4 and 8(amnion expands, formstube that encloses theconnecting stalk and aduct for blood vessels)
Head growth exceedsgrowth of other regions Retinal pigment
Future external ear
Foot plate
Upper limb differentiation (hand plates develop, then digital rays of future fingers; wrist, elbow start forming)
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7c1, p.161
WEEK 8
Placenta
WEEK 16
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7c2, p.161
Upper and lower limbs wellformed; fingers and thentoes have separated
Final week of embryonicperiod; embryo looksdistinctly humancompared to othervertebrate embryos
Tail has become stubby
Primordial tissues ofall internal, externalstructures now developed
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7d, p.161
During fetal period, length measurement extends from crown to heel (for embryos, it is the longest measurable dimension, as from crown to rump).
WEEK 16Length: 16 centimeters (6.4 inches)Weight: 200 grams (7 ounces)
WEEK 38 (full term) Length: 50 centimeters (20 inches)Weight: 3,400 grams (7.5 pounds)
WEEK 29Length: 27.5 centimeters (11 inches)Weight: 1,300 grams (46 ounces)
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Congenital Malformations
• 97% of babies are normal at birth• Birth defects can be produced by genetic
disorders or exposure to environmental agents
• Most are caused by disruptions in embryonic development
• Brain and nervous system may be damaged throughout development
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
-Teratogens are environmental agents that cause developmental disruptions
Sources of teratogens
Natural in environment
-skunk cabbage contains cyclopamine, which inhibits cholesterolbiosynthesis, preventing a key developmental pathway from working;Toxoplasma gondii - cat-borne - leads to stillbirths
Infectious agents
-Rubella (German measles), blindness, hearing loss, heart defects,mental retardation
Human introduced in the environment
-methylmercury, fungicide, central nervous system disorders, cerebral palsy, mental retardation
Drugs
-Diethylstilbesterol (DES), synthetic estrogen, used to prevent miscarriageuntil 1971 (it didn’t work), structural damage to reproductive organs, increased cancer risk
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Diethylstilbestrol (DES)
-prescribed to ~5 million women 1938-1971
-used to prevent miscarriage and preterm labor
-shown not to be effective in the 1950s, continued to be prescribed
-1970s, women exposed to DES in utero had increased cervical cancer risk, morphological abnormalities of reproductive tract
-men exposed in utero often had abnormal genitalia
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
The Effects of Teratogens
Fig. 7.8
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fetal Alcohol Syndrome (FAS)
• A serious and widespread teratogenic problem
• Fetal Alcohol Syndrome – 1.9/1,000 births
• Fetal alcohol effect 3.5/1,000 births• Preventable
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fetal alcohol syndrome-characterized by small heads, low nose bridge, small brain size, mental retardation
-third most common cause of mental retardation (after Fragile X and Down’s)
-FAS affects 1 out of 500-750 newborns in the US
FAS normal
-intellectual and behavioral problems seen even in the absence of morphologicaldefects
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Alcohol Consumption During Pregnancy Can Result in:
• Spontaneous abortion• Growth retardation• Facial abnormalities• Mental retardation• Learning disabilities