BIO 207 LECTURE 6.docx

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Biology (Biological Sciences)
Lesley Harrington

BIOL207 B01 Lec06 2013-01-18 CHAPTER 3 (cont’d) Sometimes, the genotype and phenotype don’t match; maybe a flower has a disease and cannot show the purple pigment even though it possesses the purple dominant gene. When genotype and phenotype don’t match… it’s called incomplete penetrance. A. Environmental Influences a. phenotype of some genotypes depends on the environment; b. relationship is most easily studied by measuring variation in a population (VP= V +GV ) E All that matters is that the phenotypic ratio VP= phenotypic variance VG= genotypic variance VE= environmental variance more complicated models also exist, e.g. (V = P + VG+ V E G E Variable expressivity means that we have a variation of intensities for one single genotype (different shades of purple). You can have both variable expressivity and incomplete penetrance at the same time; 2 c. quantify heritability (h ) as: h = V /V G P We can quantify variability by comparing the phenotypic variation over the variation in the genotypes 2 if environment has no influence,2h = 1.0 (complete heritability) if genotype has no influence, h = 0 (no heritability) 2 d. can measure h , V ,GV byEcontrolling either environment or genotype or both e. twin studies are alternative for human subjects, since can’t control V G V E experimentally monozygotic (identical) twins : V =G0; should have identical DNAand differences depend on environmental component; for non-twins… how much genetic variation is there and how much does genetics contribute to phenotypes. When you estimate these variables, it is important to see how much something is genetic and how much is dizygotic (fraternal) twins : VG~ 0.50; half the genetic information but otherwise influenced by phenotypic ratios Robert Plomin BBC4 interview; exam scores in twin studies Abehavioural geneticist from Chicago and works in England, working with twins in Englad; studying IQ, height, weight, body mass index How much genetics is influenced by genetics.. and how much by environment? Everything shows some genetic influence; autism is genetic influenced not environmentally… turns out identical twins are 60% similar.. if one twin is autistic, about 60% chance for the other; took autism to look at it from a social disorder but it is now highly variable in genetics through twin studies Twin studies suggest that although there is some genetic influence in alcoholism, it’s not influential (esp in female)  some people are more genetically susceptible to environmental factors Genetics is important everywhere; there is no behavioural trait that is completely heritable; if we will do molecule genetics, we need to focus on things that are more heritable Height is about 90% heritable due to nature and genetics Breast cancer doesn’t show a great deal of genetic influence Cognitive a
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