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Chapter 12.docx

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University of Toronto Scarborough
Steve Joordens

Chapter 12 Lifespan DevelopmentIntroduction chapter discusses the physical intellectual and social changes we go through as we age and some problems associated with abnormal development development does not stop at the end of childhood growing older is not only a matter of agingDevelopmental psychologists study both the similarities and the differences among people as they develop and changeDevelopmental psychologists employ speical strategies of research o CrossSectional Study A study of development in which individuals of different ages are compared at the same time easier to carry out then longitudinal study but have problem with interpretation o Longitudinal Study A study of development in which observations of the same individuals are compared at different times of their livesPrenatal Development Prenatal Period The nine months between conception and birth This period is divided into three developmental stages the zygotic the embryonic and the fetalThe length of a normal pregnancy is 266 days 38 weeks and during this time development depends on genetic contribution from egg and sperm and the epigenetic modificationGenetic contribution from the egg and sperm determines the genotype the genetic constitution of an individual organism of the new individualo Genetic material can replicate producing descendants that are genetic copies of this single cell o However Prenatal development is not simpley a cellular replication producign copies of original fertilized egg even though all cells have the same genetic content except reproductive cells each cell differs ieblood cell and muscle cellsEpigenetic modificationis a modification of cell inheritance that is not due to alterations of the DNA sequence itself o An example of epigenetic modification is X chromosome inactivation in which one of the two X chromosomes in women is silenced early in development such that most of its genes do not synthesize the proteins they normally wouldo It is not known by which mechanims the chromosome is selected but it is an important factor in development since the chromosome could be either the mothers or fathers o Epigenetic modification illustrates the point that cells chemical environment moderates the expression of its geneticStages of Prenatal Development starting point of the prenatal development is the union of the ovum egg and spermZygote Stage The first stage of prenatal devlopment during which the zygote divides many times and the internal organs being to form lasts about two weeksEmryonic Stage The second stage of prenatal development beginning at about two weeks and ending about eight weeks after conception during which the heart begins to beat the brain starts to function and most of the major body structures begin to form o Zygote is transformed into an embryo o Spinal cord starts to funcion and most of the major body structure are beginning to formo Also the stage where the embryo is most susceptible to external chemical influences Teratogens Substances agents and events that can cause birth defects rdo Sexaul development occurs 23 chromosome pair determines the sex of the emrbyoXX female and XY maleA pair of goands will become either ovaries or testes o Presence or absence of testes determines the development of the other sex organsIf testes are present they produce sex hormones called androgensAndrogens The primary class of sex hormones in males The most important androgen is testoterone this develops the male internal sex organs the penis and scrotumthe development of female sex organs occurs naturally withouta hormoneFetal Stage The third and final stage of prenatal development which lasts for about seven months beginning with the appearance of bone tissue and ending with birth rdo By the end of 3 month development of major organs is completed and the bones and muscles are beginning to develop fetus starts to kick tho End of 4 month fetus is sleeping and waking regularly movements of fetus become strong enough to be felt by mother and heartbeat is loud enough to be heard by stethoscope tho 7month is crucial because if the fetus is born it has a low chance of survivingo Last 2 months fetus gains weight at the rate of 250 g per week on average fetus is about 50 cm and 35 kg fetus is ready to be born
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