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Lecture 2

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PSYC 2500
Kim O' Neil

Lecture 2 The biology of heredity - We have 46 chromosomes - Gametes (sperm/egg cells) have 23 chromosomes each • Combination of the 2 creates a cell - When combined, they provide 23 pairs of chromosomes - The first 22 pairs of chromosomes are autosomes and the 23 pair is sex chromosomes (either X or Y) Gender determination - Gender determined by 23 chromosome pair • XX = female • XY = male - Female always donates an X chromosome, the male is the one who determines the sex by either contributing an X or Y chromosome The biology of heredity cont’d - Each chromosome is made up of DNA(deoxyribonucleic acid) - Genes are sections of the DNAstrands (50% genes from each parent) - Genotype is one’s complete set of genes - Phenotype is one’s physical, behavioral, and psychological features About genes… - Guide the production of enzymes and proteins which feed cells - Guide cell differentiation • Brain cells vs. other cells - Guide timing of development • Genetically prewired to develop in a certain way, at a certain time. Ex: when you’re going to hit puberty - Are influenced by environmental factors... but environmental factors can overwrite genetics • Ex: the relationship that a girl has with her father will determine when she starts menstruating. The results found that females who had a strained relationship with their father started their menstrual cycle sooner • Ex: nutrition and toxins are environmental factors Single gene inheritance - Pairs of alleles (genes) can be either homozygous or heterozygous (alleles differ) - Dominant allele: its chemical instructions are followed (ex: dark hair is a dominant gene) - Recessive allele: its chemical instructions are ignored (ex: blond hair is a recessive gene) • To have a recessive gene (like blond or red hair), you need to get the recessive gene from both mom and dad - Incomplete dominance: one allele doesn’t dominate the other completely (have the trait but not necessarily full blown symptoms) • May have a tendency for that trait. • Ex: sickle cell disease  Mom = healthy and unhealthy, dad = healthy and healthy  Because dad gives healthy gene, the child only gets TRAIT of it  If both mom and dad were unhealthy (recessive), the child would have full on sickle cell anemia - Codominance: genes are equally expressed (ex:AB blood type) (EXAM QUESTION!!) • Afrom mom and B from dad =AB blood type Genetic disorders - Many disorders are triggered when a child inherits two recessive alleles • Examples include cystic fibrosis, PKU (disorder which causes cognitive problems) • Most inherited disorders are very rare - If diseases were triggered by dominant alleles, everyone with at least 1 of the alleles would get the disease - Some people are born with too many, too few, or damaged chromosomes st • People with Down Syndrome usually have an extra 21 chromosome • Anumber of disorders (ex: Turner’s Syndrome, Klinefelter’s Syndrome) are caused by missing or extra sex chromosomes - Some diseases are caused by dominant genes • Huntington’s disease progressive degeneration of the nervous system. Nerves degenerate in middle age (severe muscle spasms) • Caused by a dominant allele on chromosome 4 - Hemophilia (blood doesn’t clot enough) is sex-linked, in that the sex chromosome carries the disease Detection/treatment - Genetic counseling predict the likelihood of a particular trait/disorder by looking at family history - Methods used to test for certai
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