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PSYA02H3 (932)
John Bassili (149)
Chapter 12

Chapter 12 textbook notes

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University of Toronto Scarborough
John Bassili

Chapter 12 LIFESPAN DEVELOPMENT - We recognize now that development does not stop at the end of childhood. - Growing older is a matter not only of aging, but also of changing personally, intellectually, and socially - Developmental psychologists study both the similarities and the differences among people as they develop and change - Since they study change, developmental psychologists employ special strategies of research - Cross-sectional study individuals of different ages are simultaneously compared with respect to some test or observation - ex) a developmental psychologist might present mathematical problems to groups of five-, seven-, and nine-year-olds to measure the childrens grasp of the concept of negative numbers - In contrast, a longitudinal study compares observations of the same individuals at different times of their lives - a longitudinal study of childrens grasp of negative numbers might test a group of children when they were five years of age, and then repeat the test on the same children at seven and then at nine - Cross-sectional studies are usually more convenient to carry out, and they avoid the problems associated with repeatedly testing or observing the same individuals - However, they contain a subtle problem in interpretation Prenatal Development - The prenatal period extends over the approximately nine months between conception and birth - During the pregnancy (266days or 38 weeks), development depends on two factors whose effects characterize themes of this chapter -There is the genetic contribution from egg and sperm that determines the genotype of the new individual - Genetic material can replicate, producing descendants that are genetic copies of this single cell - A child develops from this single source of genetic instructions - Prenatal development, however, is not simply a matter of cellular replication producing copies of the original fertilized egg - Although all cells of an individual (with the exception of reproductive cells) have the same genetic content, they obviously differ - ex) blood cells are not the same as neurons and muscle cells are not the same as those that produce bone - Some factor must direct the mechanisms of replication during the prenatal period so that cells that are genetically identical will develop along different paths - X chromosome inactivation is one example of this factor at work - One of the two X chromosomes that women bear is silenced early in development, such that most of its genes do not synthesize the proteins they normally would www.notesolution.com - Inactivation of one X chromosome is important because it limits the total amount of proteins produced by genes located on the X chromosome - Without this limit, the metabolism of a developing female would be very different from that of a developing male (who has only one X chromosome) - X chromosome inactivation occurs early in the development of females and affects all subsequent cellular reproduction the silenced chromosome is passed along to descendant cells, but it remains silenced - X chromosome inactivation is one example of an epigenetic modification, a modification of cell inheritance that is not due to alteration of the DNA sequence it self Stages of Prenatal Development - The union of the ovum (egg) and sperm, conception, is the starting point for prenatal development - During the zygote stage which lasts about two weeks, the zygote, or the single new cell that is formed at conception, divides many times, and the internal organs begin to form - By the end of the first week, the zygote consists of about a hundred cells - Many of the cells are arranged in two layers, one for the skin, hair, nervous system, and sensory organs and the other for the digestive and respiratory systems and glands - Near the end of this stage, a third layer of cells appears that will eventually develop into muscles and the circulatory and excretory systems - The embryonic stage of prenatal development, the second stage, begins at aabout two weeks and ends about eight week s after conception - During this stage, the zygote is transformed into an embryo and development occurs at an incredibly rapid pace - By a month after conception, a heart has begun to beat, a brain and spinal cord have started to function, and most of the major body structures are beginning to harm - By the end of this stage, the major features that define the human body- arms, hands, fingers, legs, toes, shoulders, head, and eyes are discernible. - Behaviorally, the embryo can react reflexively to stimulation - ex) if the mouth is stimulated, the embryo moves its upper body and neck - Because so many changes depend on a delicate chemical balance, the embryo at this stage is most susceptible to external chemical influences, including alcohol and other drugs, or toxins produced by diseases such as rubella - These substances are teratogens (any substance, agent, or event that can cause birth defects) - The begrdning of sexual development occurs during the embryonic stage - The 23 chromosome pair determines the sex of the embryo - The female partner contributes and X to this pair at conception, whereas the male partner contributes either an X or a Y chromosome www.notesolution.com
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