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

Differentiation and development Gradual modification of physical and physiological characteristics Differentiation The creation of different types of cells

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

Fertilization (conception) Occurs in the uterine tubes Within a day of ovulation Spermatozoa cannot fertilize an ovum until after capacitation

Figure 27.1 Fertilization Figure 27.1a

Figure 27.1 Fertilization Figure 27.1b

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

Oocyte activation Oocyte completes meiosis II Functionally mature ovum Female pronucleus and male pronucleus fuse (amphimixis) Polyspermy prevented by membrane depolarization and cortical reaction

Embryonic and Fetal Periods Induction During prenatal development differences in cytoplasmic composition trigger changes in genetic activity Gestation periods Three trimesters

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

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

Figure 27.2 Cleavage and Blastocyst Formation

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

Figure 27.3 Stages in Implantation PLAY Animation: Location of the Endometrium Figure 27.3

Figure 27.4 The Inner Cell Mass and Gastrulation

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

Extraembryonic Membranes Four extraembryonic membranes: Yolk sac Amnion Allantois Chorion

Figure 27.5 Extraembryonic Membranes and Placenta Formation Figure 27.5a, b

Figure 27.5 Extraembryonic Membranes and Placenta Formation Figure 27.5c, d

Figure 27.5 Extraembryonic Membranes and Placenta Formation

Embryo Anatomy Yolk sac Important site of blood cell formation Amnion Encloses fluid that surrounds and cushions developing embryo Allantois Eventually becomes bladder Chorion

Figure 27.6 A Three-Dimensional View of Placental Structure

Placentation Chorionic villi extend into maternal tissue Forms intricate branching network for maternal blood Umbilical cord connects fetus to placenta

Hormones of the placenta Trophoblast secretes hormones to maintain pregnancy HCG Estrogens Progesterone hPL Placental prolactin Relaxin

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

Figure 27.9 The Second and Third Trimesters Figure 27.9a, b

Figure 27.10 Growth of the Uterus and Fetus Figure 27.10a, b

Figure 27.10 Growth of the Uterus and Fetus Figure 27.10c, d

Developing fetus totally dependent on maternal organs Maternal adaptations include increased Respiratory rate Tidal volume Blood volume Nutrient and vitamin uptake Glomerular filtration rate

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

Figure 27.11 Factors Involved in the Initiation of Labor and Delivery

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

Figure 27.12 The Stages of Labor

Postnatal life stages Neonatal period Infancy Childhood Adolescence Maturity Senescence begins at maturity and ends in death

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

Figure 27.13 The Milk Let-Down Reflex

Figure 27.14 Growth and Changes in Body Form

Adolescence Begins at puberty The period of sexual maturation Ends when growth is completed

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

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

Senescence Aging affects functional capabilities of all system

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

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

Figure 27.15 Human Chromosomes

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

Figure 27.16 Predicting Phenotypic Characteristics by Using Punnett Squares Figure 27.16a, b

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

Sources of individual variation Genetic recombination Gene reshuffling Crossing over and translocation Occurs during meiosis Spontaneous mutations Random errors in DNA replication

Figure 27.17 Crossing over and Translocation Figure 27.17a-c

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

Figure 27.18 X-Linked inheritance

The Human Genome Project Mapped more than 38,000 of our genes Including some responsible for inherited disorders

Figure 27.19 A Map of the Human Chromosomes

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

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