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29 Development and Inheritance C h a p t e r
PowerPoint® Lecture Slides prepared by Jason LaPres Lone Star College - North Harris Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Differentiation and development
Gradual modification of physical and physiological characteristics Differentiation The creation of different types of cells
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Stages of development Prenatal development Embryological
Changes occurring the first two months after fertilization Fetal Begins at the start of the ninth week and continues until birth Postnatal development Commences at birth and continues to maturity
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Fertilization (conception)
Occurs in the uterine tubes Within a day of ovulation Spermatozoa cannot fertilize an ovum until after capacitation
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Figure Fertilization Figure 27.1a
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Figure Fertilization Figure 27.1b
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The Oocyte at Ovulation
Oocyte is in meiosis II Surrounded by the corona radiate Spermatozoa release hyaluronidase and acrosin Enzymes required to penetrate corona radiate Single spermatozoan contacts oocyte, fertilization begins Oocyte activation PLAY Animation: Fertilization and Oocyte activation
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Oocyte activation Oocyte completes meiosis II Functionally mature ovum
Female pronucleus and male pronucleus fuse (amphimixis) Polyspermy prevented by membrane depolarization and cortical reaction
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Embryonic and Fetal Periods
Induction During prenatal development differences in cytoplasmic composition trigger changes in genetic activity Gestation periods Three trimesters
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The First Trimester Cleavage
Zygote becomes a preembryo then a blastocyst Implantation Blastocyst burrows into uterine endometrium Placentation Blood vessels form around blastocyst and placenta develops Embryogenesis Formation of a viable embryo
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Cleavage and blastocyst formation
A series of cell divisions that subdivides the cytoplasm of the zygote Trophoblast – outer layer of cells Inner cell mass – cluster of cells at one end of blastocyst
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Figure 27.2 Cleavage and Blastocyst Formation
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Implantation Occurs about 7 days after fertilization
Trophoblast enlarges and spreads Maternal blood flows through open lacunae Gastrulation Embryonic disc composed of germ layers Endoderm Mesoderm Ectoderm
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Figure 27.3 Stages in Implantation
PLAY Animation: Location of the Endometrium Figure 27.3
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Figure 27.4 The Inner Cell Mass and Gastrulation
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Germ layers Gastrulation
By day 12 surface cells move toward the primitive streak A third germ layer forms The three germ layers are: Ectoderm – superficial cells that did not migrate Endoderm – cells facing the blastocoele Mesoderm – migrating cells between ectoderm and endoderm
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Extraembryonic Membranes
Four extraembryonic membranes: Yolk sac Amnion Allantois Chorion
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Figure 27.5 Extraembryonic Membranes and Placenta Formation
Figure 27.5a, b
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Figure 27.5 Extraembryonic Membranes and Placenta Formation
Figure 27.5c, d
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Figure 27.5 Extraembryonic Membranes and Placenta Formation
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Embryo Anatomy Yolk sac Important site of blood cell formation Amnion
Encloses fluid that surrounds and cushions developing embryo Allantois Eventually becomes bladder Chorion
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Figure 27.6 A Three-Dimensional View of Placental Structure
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Placentation Chorionic villi extend into maternal tissue
Forms intricate branching network for maternal blood Umbilical cord connects fetus to placenta
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Hormones of the placenta
Trophoblast secretes hormones to maintain pregnancy HCG Estrogens Progesterone hPL Placental prolactin Relaxin
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Second and Third Trimesters
Second trimester Organ systems increase in complexity Third trimester Many organ systems become fully functional Fetus undergoes largest weight change At end of gestation fetus and uterus push maternal organs out of position
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Figure 27.9 The Second and Third Trimesters
Figure 27.9a, b
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Figure 27.10 Growth of the Uterus and Fetus
Figure 27.10a, b
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Figure 27.10 Growth of the Uterus and Fetus
Figure 27.10c, d
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Developing fetus totally dependent on maternal organs
Maternal adaptations include increased Respiratory rate Tidal volume Blood volume Nutrient and vitamin uptake Glomerular filtration rate
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Structural and Functional Changes in the Uterus
Progesterone inhibits uterine muscle contraction Opposed by estrogens, oxytocin and prostaglandins Multiple factors interact to produce labor contractions in uterine wall
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Figure 27.11 Factors Involved in the Initiation of Labor and Delivery
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Goal of labor is parturition
Stages of labor Dilation The cervix dilates and fetus moves toward cervical canal Expulsion The cervix completes dilation and fetus emerges Placental Ejection of the placenta
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Figure 27.12 The Stages of Labor
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Postnatal life stages Neonatal period Infancy Childhood Adolescence
Maturity Senescence begins at maturity and ends in death
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The neonatal period From birth to one month
Respiratory, circulatory, digestive and urinary systems adjust Infant must thermoregulate Maternal mammary glands secrete colostrum first few days Milk production thereafter Both secretions are released via the milk let-down reflex Body proportions change during infancy and childhood
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Figure 27.13 The Milk Let-Down Reflex
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Figure 27.14 Growth and Changes in Body Form
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Adolescence Begins at puberty The period of sexual maturation
Ends when growth is completed
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Puberty marked by Increased production of GnRH
Rapid increase in circulating FSH and LH Ovaries and testes become sensitive to FSH / LH Gamete production initiated Sex hormones produced Growth rate increases
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Hormonal changes at puberty produce gender specific differences in system
Differences are retained throughout life Adolescence continues until growth completed Further changes occur when sex hormones decline Menopause Male climacteric
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Senescence Aging affects functional capabilities of all system
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Genes and chromosomes Every somatic cell carries copies of the 46 original chromosomes in the zygote Genotype – Chromosomes and their component genes Phenotype – physical expression of the genotype
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Patterns of inheritance
Somatic cells contain 23 pairs of chromosomes Homologous chromosomes 22 pair of autosomes and one pair of sex chromosomes Chromosomes contain DNA Genes are functional segments of DNA
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Figure 27.15 Human Chromosomes
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Various forms of a gene are called alleles
Homozygous if homologous chromosomes carry the same alleles Heterozygous if homologous chromosomes carry different alleles Alleles are either dominant or recessive depending on expression Punnett square diagram predicts characteristics of offspring
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Figure 27.16 Predicting Phenotypic Characteristics by Using Punnett Squares
Figure 27.16a, b
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Inheritance Simple inheritance
Phenotypic characteristics are determined by interactions between single pair of alleles Polygenic inheritance Phenotypic characteristics are determined by interactions among alleles on several genes
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Sources of individual variation
Genetic recombination Gene reshuffling Crossing over and translocation Occurs during meiosis Spontaneous mutations Random errors in DNA replication
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Figure 27.17 Crossing over and Translocation
Figure 27.17a-c
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Sex-linked inheritance
Sex chromosomes are X chromosome and Y chromosome Male = XY Female = XX X chromosome carries X-linked (sex linked) genes Affect somatic structures Have no corresponding alleles on Y chromosome
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Figure 27.18 X-Linked inheritance
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The Human Genome Project
Mapped more than 38,000 of our genes Including some responsible for inherited disorders
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Figure 27.19 A Map of the Human Chromosomes
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You should now be familiar with:
The relationship between differentiation and development, and the various stages of development The process of fertilization The three prenatal periods and describe the major events associated with each The importance of the placenta as an endocrine organ
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You should now be familiar with:
The structural and functional changes in the uterus during gestation The events that occur during labor and delivery The basic principles of genetics as they relate to the inheritance of human traits
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