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PSYCH 2AA3 (70)
Chapter 2

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Jennifer Ostovich

Section 1: Sept 5 to Oct 3 Textbook Readings Chapter 2: Behavioural Genetics 2.1 Mechanisms of Heredity The Biology of Heredity  Egg and sperm are gametes- have 23 chromosomes while other cells in the body have 46  5 ml of semen is ejaculated during intercourse into the vagina releasing 200-500 million sperm- Only a few hundred of these sperm actually complete the 15-20 cm journey through fallopian tubes  Louise Brown – created first ‘test-tube’ baby conceived in a lab dish instead of in her mother’s body. Today used more than 130 000 times in America  In vitro fertilization involves mixing sperm and egg together in a lab dish and then placing several fertilized eggs in the mother’s uterus w/I 24 hours of fertilization  Only about 1/3 of attempts at in vitro fertilization succeed, more likely to have twins, have baby with low weight or birth defects, expensive procedure  First 22 pairs of chromosomes are called autosomes and the 23 pair determines the sex of the child XX for girl, XYmale  Each chromosome contains one molecule of DNA- each group of nucleotide bases that provides a specific set of biochemical instructions is called a gene  46 chromosomes contain approx 25 000 genes  The complete set of genes makes up a person’s heredity is known as their genotype  The physical behaviour and physcological features of these genes are called phenotypes Single Gene Inheritance  Genes come in different forms that are known as alleles- instructions  The alleles in the pair of chromosomes are sometime the same, which makes them homozygous, when they differ they would be heterozygous – heterozygous involve dominant and recessive genes  Sometimes one allele does not dominate another completely- incomplete dominance. The phenotype that results often falls between the phenotype associated with either allele  The impact of heredity depends on enviri e.g. sickle cell anemia and malaria Genetic Disorders Inherited Disorders  Relatively few serious disorders are caused from dominant alleles b/c not evolutionary advantageous therefore dominant alleles that produce fatal disorders soon vanish from species  exception is huntington’s disease: a fatal disease characterized by progressive degeneration of the nervous system, dominant allele found on chromosome 4. Usually signs don’t occur until middle age and they’ve already had children  Some disorders are sex-linked, where the gene causing the disorder is carried on one of the sex chromosomes e.g. hemophilia is carried on X gene therefore most commonly expressed in males and females being carriers. Allele is recessive . Abnormal Number of Chromosomes  Development is disturbed if an individual is born with extra, missing or damaged chromosomes st  Down Syndrome: caused by an extra 21 chromosome and results in cognitive deficits and developmental delay- the mother who provides an extra chromosome  The odds that a women will bear a child with down syndrome increases markedly as she gets older  Most eggs that could not develop normally are removed naturally 2.2 Heredity, Environment, and Development Behavioural Genetics  The branch of genetics that deals with inheritance of behavioural and psychological traits  Complicated because genotypes are usually associated with an array of behavioural outcomes i.e. putting people in a range of introversion to extraversion (it’s a spectrum)  Polygenic inheritance: combined activity of many separate genes Methods of Behavioural Genetics  MZ twins identical genes, DZT 50% same as normal siblings  In twin studies scientists compare identical and fraternal twins to measure the influence of heredity  If identical twins are more alike than
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