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Development and aging Fertilization- joining of egg and sperm nuclei Only one sperm should enter the egg

Development and aging Fertilization- joining of egg and sperm nuclei Only one sperm should enter the egg. Zygote- fertilized egg Embryo- the zygote starts dividing Embryonic membrane starts to produce hCG (human chorionic gonadotropin) Pregnancy test detects hCG in urine

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Development and aging Fertilization- joining of egg and sperm nuclei Only one sperm should enter the egg

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  1. Development and aging • Fertilization- joining of egg and sperm • nuclei • Only one sperm should enter the egg

  2. Zygote- fertilized egg Embryo- the zygote starts dividing Embryonic membrane starts to produce hCG (human chorionic gonadotropin) Pregnancy test detects hCG in urine Secreted by corpus luteum, then placenta (see p. 533)

  3. Early stages of development Cleavage cells start to divide Morphogenesis distinct shapes start to appear Differentiation distinct cells and tissues Growth cells get bigger and so does embryo

  4. “Germ layers” Give rise to all tissues and organs Ectoderm- skin epidermis, nervous system etc. Mesoderm- muscles, connective tissue Endoderm- lining of various organ systems secreting organs

  5. “Extraembryonic membranes” Amnion- provides fluid environment for fetus Yolk sac- site of blood cell formation Allantois- develops into circulatory system Chorion- develops into placenta

  6. Some milestones of development Embryonic- second through eighth week all major organ systems are present Fetal development- from third month organ development and growth Stem cells are active Sex of fetus is determined by X and Y chromosomes

  7. Birth Positive feedback Uterine contractions; oxytocin Oxytocin also plays a role in lactation

  8. Neonatal stage- about four weeks Lungs are collapsed; circulation bypasses them First breath counts! Surfactant is critical to reduce surface tension in alveoli; allow inflation of lungs Body temperature, electrolyte balance is temporarily unstable Circulatory system changes

  9. Developmental defects Aneuploidy (“wrong” number of chromosomes) Karyotyping- chromosomal analysis Down syndrome- trisomy 21 Edwards syndrome- trisomy 18 Patau syndrome- trisomy 13 Triploidy- an extra set of chromosomes

  10. Abnormal number of sex chromosomes XO- Turner syndrome XXY- Klinefelter syndrome XYY syndrome Arises due to “mistakes” in meiosis Developmental problems- spontaneous or due to exposure to harmful substances (teratogens)

  11. Fetal screening Amniocentesis CVS (chorionic villus sampling) Screening eggs

  12. Proper fetal development depends on: Nutrition Freedom from infection Avoidance of drugs and alcohol Avoidance of smoking lowers vitamin levels substances in smoke can cross placental barrier

  13. Development does not stop at birth! Neonate- rapid growth and neurological development Puberty- sexual maturation “Secondary sexual characteristics” Aging-?

  14. A few words about genetics • Children inherit genes from both parents • Genes affect appearance and health • Some genetic traits are influenced by the environment • Karyotype- analysis of chromosome structure

  15. Modes of inheritance • Dominant or recessive • Autosomal or X-linked • Pedigrees are useful to determine patterns-linked • Punnett squares are used to predict probabilities

  16. Inheritance can be complex • Some traits affected by single genes (either/or) • Some affected by multiple genes (polygenic) • Some affected by environment as well as genes (multifactorial) • Genes can be analyzed at the DNA level also

  17. Summary • Growth and development include increases in size as well as changes over time • Aging involves accumulated damage as well as programmed cell death • Genetics is the study of inheritance • Influences health and diversity among humans • Interaction of genes and the environment is an important area of study

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