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Lecture 1 - Research Methods - Behavioural Genetics

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PSYC 2110
Maxine Wintre

Class Notes (Nature Side) - September 23, 2010 1 Research Methods - Lab research (can manipulate the variables) - Naturalistic research (observe behaviour) - Experimental research (highly controlled) - Correlational research (no cause/effect) o Study cause/effect by random group/sample assignment (in experimental/control groups) - Theory guided research (should choose appropriate design; questionnaires might not be appropriate for all ages) - Atheoretical Research Sampling Strategies - Cross section research - Longitudinal research - Case studies 3 types of reliability - Test-retest reliability - Interrater reliability - Consistency/reliability across subjects/children = generalized reliability Behavioural Genetics Gregor Mendel 1865-1900 (19 century monk) - Creative notion = idea of not averaging the traits from the mother/father in the offspring - Offspring didn’t indicate average of traits of parents - Males are males; not average of female/males - Transmitted discretely from one generation to the other - Took a group of tall flowers / short flowers and cross fertilized st o TT x tt  100% looks tall [1 generation – dominant T gene; phenotype would look the same but genotype is different] o Tt x Tt  1 (short): 3 (tall) [2 generation – mostly dominated by genotype)  TT (tall) + Tt (tall) + tT (tall) + tt (short)  Phenotype = characteristics that individual portrays (what they look like; observational feature)  Genotype = genetic composition responsible for that phenotype Phenotype Vs Genotype - Some genes are dominant genes (T), some genes are recessive genes, only be obvious from phenotype/appearance if there were 2 recessive genes - If there’s 1 dominant gene, that will be expressed in genotype, therefore looks tall - Phenotype can be influenced by the environment - Genes set a potential/limits; but environment determines if those limits are achieved Dominant Vs Recessive Genes - Dominant genetic attribute = dark hair, curly hair, normal sight (normal colour vision), normal blood (RH+ factor), Huntington disease (dementia; random jerking movements – express symptoms in middle age) o On the type of chromosome #4 (hard to get to) 1 Class Notes (Nature Side) - September 23, 2010 2 - Recessive genetic attribute = red/light hair, straight hair, blue eyes, haemophilia, patch-baldness, colour blindness, diabetes, some forms of childhood muscular dystrophy - Most are determined by polygenetic (by number of genes which influence in an additive way) Homozygous Vs Heterozygous - Ex: TT (only dominant gene) tt (only recessive gene)  Tt (heterozygous) Polygenetic - Influenced by many different genes - Should be normally distributed in the population o Mean median mode are the same point (the line right in the middle, divide frequency in half) o -1Standard Deviation - +1SD = 68% o Mean – +1SD = 34% o -2SD – +2SD = 95% o >+2SD = 2.5% o Y = characteristic frequency - Ex: knowledge is polygenetic The Human Genome Project - 100 thousands genes of human in DNA - Want to find location, chemical composition, sequence, what they are contributed to, what their function - No 100 000 genes, 20-30 thousand genes - Genes are responsible for alzemeir, schizophrenia, manic depression, breast cancer, psychological tendency to follow orders, to male homosexuality - There are a lot of ethical considerations in this project - You carry the gene doesn’t mean you will have the outcome DNA – deoxyribonucleic acid Sex Determination - 23 pairs of chromosome of human cell Autosomes - 1 22 pairs are called autosomes - 23 pair contains the sex hormone - Every normal female has 2 X chromosome; Every normal male as 1 X 1 Y chromosome Mitosis / Meiosis Fertilization Conception - When sperm penetrates the ovum/egg of a female - Result of ovum penetrated of sperm = zygote Zygote - Half sperm carries X chromosome; half sperm carries Y chromosome 2 Class Notes (Nature Side) - September 23, 2010 3 - Sperms carried by X chromosome are a bit larger (larger head) - Sperms carried by Y chromosome have shorter tails (faster swimmers) - For every 100 female conceived, 160 males are conceived - By birth, for 100 girls that are born, only 105 males are born - Male is more likely to suffer from miscarriage; have higher death rates and shorter life spans - By adolescence, for every 100 females, there are 100 males - Artificial semindation can determine sex of a child (but consider ethical consideration) - Technology can separate the X or Y chromosome of a sperm - Why males are more easily to encounter early problems? o Y chromosome (an arthmissing from the chromosome that forms look like an X) o If gene placed in 4 arm of the X chromosome, there are no counter parts in the Y chromosome (missing arm) o If something wrong happens to the 4 arm of X chromosome, no other way to generate that gene from the Y (therefore guys are more fragile) o The missing support of the Y chromosome make male fetus more fragile o X chromosomes that don’t have a match from Y chromosome = sex-link genes o Traits that they demonstrate in phenotype = sex-link traits - A recessive gene (tt) which normally would be repressed by a dominant gene in a pair, would be expressed in the phenotype if it is a sex-link gene or if it’s a male Sex Linked Disorder (1) haemophilia (bleeder disorder) - Deficiency in blood plasma (needed for blood clotting) - Won’t heal if person gets a cut - Genetically present in the royal family of Europe, Russia, Germany - Royal families marry with non royals now to get rid of this disorder (2) red-green colour blindness - Male are more frequently experienced - Female to be colour blind; inherent colour blindness gene from both parent - male to be colour blind, only inherent the color blindness gene from the mother (on the X chromosome, not Y) (3) Duchene type muscular dystrophy Congenital Vs Inherited Genetic Disorders Chromosome Anomaly - Down Syndrome (Trisome 21, Mongolism) - Usually have narrowed slanted eyes, flat nose, extra fold of skin on the eyelid, small round head, small mouth with droopy corner, thick tongue, short finger, poor muscle tone, always have an IQ of <50 (normal = 100; SD of 15) congenital heart defect, shorter life span - When chromosome pair 21 appears as triplet, instead of a pair - Individuals have 47 chromosomes, as opposed to 46 - Occur during cell division, when cell don’t divide (non-disjunction) o Appears to be related to maternal age o As women get older, tendency to difficulty of non disjunction 3 Class Notes (Nature Side) - September 23, 2010 4 o Overall = 1/660 births. <29 = 1/3000. 45+ = 1/40 - Can be diagnosed in each pregnancy o If women is >35, OHIP covers the test Genetic Counselling Amniocentesis - Sample cells from amnionic fluid from embryo sac through women’s abdomen - Fluid can be tested to see what the genetic composition is - 15 weeks +, enough fluid to take the sample by needle - Take 2-3 weeks to process for result - Women is at least 16 weeks of pregnant (4months), if abort, safest is to do within the first 3 months Chorionic Villi Sampling th - Painless procedure done in a doctor’s office in 5 week of pregnancy - Women don’t know they’re pregnant until 6+ weeks - Inserts a long thin tube through the vagina into the uterus (tube is with an ultra monitor) - Tube removes some chorionic villi (finger-like projection that are in embryonic sac, transfer oxygen, nutrients and wastes between the mother and the embryo) - Tiny chorionic villi sample = same cell as the fetus - Test genetic of chorionic villi, then will know genetic o
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