HLTB02 Chapter 3.docx

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University of Toronto Scarborough
Health Studies
Caroline Barakat

Chapter 3: Genetic Bases of Child  Development  3.1: MECHANISMS OF H EREDITY The Biology of Heredity • Each meiotic division in girls results in the production of one, viable egg and three that die off immediately • Each meiotic division in boys produces four sperm • 20% of in vitro fertilization succeeds o Likely to have twins or triplets • Genotype along with environmental influences makes up a person’s phenotype Single Gene Inheritance • Single nucleotide polymorphisms o Faulty instructions for protein production o May be found in segments of DNAnot responsible for coding proteins and can have an impact on other aspects of genetic expression in the these circumstances • Endogamy o Tendency to preferentially mate with people of the same social or cultural group o One reason why people might share physical and other genetic traits • Clinal variation o Continuous genetic variation observed between geographic regions Behavioural Genetics • Polygenic inheritance o When phenotypes reflect the combined activity of many separate genes o We cannot trace the contribution of each gene directly Methods of Behavioural Genetics • Monozygotic twins have the same genotype • Dizygotic twins come from two separate eggs fertilized by two separate sperm o Half their genes are the same • CONS of twin and/or adoptive studies o Require very large samples of children  Hard to obtain for rare disorders o Require that an investigator have an idea before beginning the study about which chromosomes to search for and where • Genetic influence is strongest in intelligence, psychopathology and personality • Heredity important in depression and schizophrenia The Nature of Nature • Nonshared environmental influences o Experiences and circumstances within a family that make siblings different from one another o Eg. parents may be more affectionate with one child than another • Heredity has a sizeable influence on such different aspects of development as intelligence and personality o Never the SOLE determinant of behavioural development 3.2: GENETIC DISORDERS Inherited Disorders • Sickle-cell disease affects people who inherit two recessive alleles o Homozygous recessive • Few serious disorders are caused by dominant alleles because: o Every person with at least one of these alleles would have the disorder o Those infected might not live long enough to reproduce o EXCEPTION: Huntington’s disease  Fatal disease characterized by progressive degeneration of the nervous system  Develop normally through childhood, adolescence, and young adulthood  Middle age, nerve cells begin to deteriorate • Muscle spasm, depression, and significant changes in personality • Usually occur after having children and these children mostly go on to develop this disease themselves • Inherited disorders are rar
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