Exam II Outline.docx

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BIOL 133
Denise Woodward

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Exam II Outline Chapter 7 Multifactorial Traits Genetic Determinism •The idea that our genes solely determine who we are. *Two factors responsible for variation in organisms – genes and environment* •Mendelian traits - trait due to single gene •Multifactorial traits - traits influenced by environment (environment and genes both affect each other •Polygenic traits - due to activity of >1 gene-- more than 2---- Multifactorial goes hand in hand •Mendelian traits: "either/or" pattern of inheritance- only 2 results •Ex: Pea plants: purple or white. People: Huntington’s disease or not. Polygenic Traits •Continuously varying *Bell Curve distribution of phenotypes About 180 genes determine height •Quantitative trait loci (QTLs): the bell shape distribution traits cardiovascular disease, height, skin color •It is difficult to predict recurrence for polygenic traits. Empiric Risk: risk calculations -- estaminets based on risk •predictions of recurrence based on trait's incidence in specific population •Incidence – rate at which event occurs •Prevalence – number of individuals who have a disorder at a specific time •based on observations/epidemiological studies Empiric Risk for Cleft Lip Relationship Recurrence Risk General population 0.1% First cousin 0.3% Niece or nephew 0.8% Child 3.5% Sibling 4.1% Identical twin 40.0% Heritability •% of phenotypic variation due to genes --- H •H=1 genes only •H=0 environment only •Correlation coefficient – proportion of genes relatives share Heritability •Proportion of people sharing a trait compared to proportion predicted to share trait. Relationship Degree Percent shared genes Siblings 1* 50% Parent and child 1* 50% Uncle/aunt and niece/nephew2* 25% Grandparent and grandchild 2* 25% First cousins 3* 12.5% ^ correlation coefficient Heritability •Example: 100 pairs of siblings. –Mendelian trait: expect it in 50 sibling pairs. –If trait is only observed in 37 pairs, the heritability = .37/.50 = .74 or 74% Observed/Expected •Heritability is component of phenotype attributed to genes. •In lab animals and plants – heritability is easy to determine. •Humans are not so easy. Adoption Studies •Adopted people share environment but not genes with adoptive family •Share genes but not environment with biological parents Twin Study •Better information than adoption studies •Concordance - % of pairs in which both twins express the trait SNP (single nucleotide polymorphism) ---- looking at parts of DNA that are different, 99.9% of DNAis the same, .1% are the differences Nucleotide site with more than one allele is a polymorphism. Site is polymorphic if allele is present in >1% of the population. •On average between two random individuals, there is one SNP every 1000 bases => 3 million differences! Genome-wideAssociation Studies •Studies which compare group of interest (cases) to control group for presence of SNP. •Controls are matched: age, ethnicity, gender, environment. •If SNP is present more often in cases than controls, it is associated with trait and implies SNP may be near gene impacting trait. Examples of Multifactorial Traits •Heart disease •Height •Intelligence •Weight •Skin color •Etc . Example: Body Weight •Leptin, ghrelin, and other proteins: hormones that control appetite •Genome-wide study results: weight is multifactorial •Environment: Example: Pima Indians ofArizona and Mexico Chapter 8 Behavior •Behaviors transmitted from parent to child. –What proportion of behavior is due to genes? –What proportion of behavior is learned? •Behavioral genetics: study of genes involved in development and regulation of nervous system. Brain is composed of neurons - Sensory neurons bring information to brain - Motor neurons send information outward to muscles. Transmitting neuron (presynaptic neuron) Receiving neuron (postsynaptic neuron) Genes that affect neurotransmission and signal transduction are good candidate genes for behavior Behavioral Genetics •understand both genetic and environmental contributions to variations in human behavior •Difficulties: –defining behaviors –measurement of behavior –complex –heritability measures apply only to population studied in particular environment Evidence Behavior has genetic component •Species specific behaviors •Behaviors breed true •some behaviors run in families Genotype =/= Phenotype Cloned Mammals --8---- clone does not mean exact replica •Dolly the Sheep – first cloned mammal •Ian Wilmut – 4 cloned sheep “are genetically identical to each other and yet are very different in size and temperament, showing emphatically that an animal’s genes do not ‘determine’ every detail of its physique and personality” Most behavioral traits are multifactorial •Attention deficit/Hyperactivity disorder (ADHD) •Siblings of affected child: 3-5x risk than those without affected sibling •Twins studies: ~ 80% heritability •Dopamine pathway may be involved Eating disorders are behavioral trait •Anorexia nervosa –psychological perception of obesity and intentional starvation •Bulimia –psychological perception of obesity and intentional vomiting •Muscle dymorphia –psychological perception of small muscle mass Anorexia nervosa •Women in U.S. have .5 - 1% lifetime risk •Risk of mortality: 15-21% •2.5% risk of second eating disorder. •10% of cases are males •Heritability of 0.5 - 0.8 –e.g. 9/16 MZ twins concordant versus 1/14 DZ twins •Candidate genes: –gene for leptin – regulates appetite –gene for serotonin – regulates mood, appetite –gene for dopamine – emotional response, pain pleasure Intelligence •Alfred Binet developed IQ test to predict academic success of developmentally handicapped children •Stanford University modified for white, middle-class Americans •IQ is normally distributed around a mean of 100. below 50 severe mental retardation 50-70 mild mental retardation 85-115 average above 115 above average MAOAdeficiency •defect on X chromosome, in gene for production of monoamine oxidase A (MAOA). •MAOAhelps metabolize serotonin, dopamine and noradrenaline •Those with the defective gene show a decrease in the enzyme's (MAOA) activity. •Impulsive killers and violent offenders have been shown by Dr. Markku Linnoila, scientific director of the National Institute on AlcoholAbuse andAlcoholism, to have low serotonin levels. •Adult mice deficient in MAOAshow a pattern of enhanced aggression •Violent behavior often runs in families. Chapter 9 DNAStructure and Replication DNA 2 important properties? Discovery of a “transforming principle” •Griffith’s experiment, 1928 •Pneumonia infects mice - mice die. •2 types of bacteria: –R (rough) - no pneumonia –S (smooth)- pneumonia What is “transforming principle”? •Conclusion: DNAis transforming principle. (Avery, MacLeod & McCarty, 1944) Heat-killed S bacteria “transformed” R bacteria to form that causes pneumonia Nucleotides are composed of: DNA: chain of nucleotides •Base - adenine (A), thymine (T), guanine (G), cytosine (C) •Sugar - deoxyribose •
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