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Lecture 4

BIOC14Winter2013 Lecture 4 Notes.docx

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University of Toronto Scarborough
Biological Sciences
Patrick Mc Gowan

BIOC14Winter2013 Lecture 4 Notes CHAPTER 7 : GENES AND ENVIRONMENT Imprinted genes – DNA methylation required o Genetic imprinting occurs mostly in mammals o Genetic imprinting = an epigenetic process leading to monoallelic gene expression without altering the genetic sequence  methylation silences one gene, so that only one other gene is expressed o These epigenetic marks are established in the germline and are maintained throughout all somatic cells of an organism o Non-mammals in general do not have imprinted genes o Example: Prader-WIlli and Angelman Syndromes o Broth syndromes are associated with loss of chromosomal region 15q11-13 o For future: find a way to unmethylate the normal gene (because person will have one healthy gene and one disease gene) so that only the healthy gene is expressed and the diseased gene is methylated Darwin’s Finches o About 14 different species of finches, each living in different habitats on the Galapagos islands o The main difference is their beak shape which is adapt to ideal shape for eating different diets like seeds, insects, flowers etc. o Adaptive radiation : a single progenitor species gives rise to multiple species through evolution o Depending on what food is available, finches became adapted to their niche  beak shape and sized changed over time to allow for feeding and therefore survival  lead to speciation o Hypothetical example: bird lives on ground and eats insects and has long pointed beak  environmental change (draught) reduces the number of insects  birds that are slightly more agile and better at catching flying insects now have a higher chance of survival (birds with shorter beaks) so eventually there will be more short beaked birds than long beaked birds  new bird population may move to a different habitat (from ground to trees for example) and so speciation occurs Charles Darwin (1809-1882) o Theory of evolution o Individuals vary  differences are inherited  many more individuals are produced that survive and reproduce  favourable variants will leave more offspring (survival of the fittest) o These facts create an inevitable process (evolution) that will modify organisms and species over time Natural Selection and Sexual Selection o Some traits have specialized roles for reproductive success o Sexual selection acts on traits that enhance reproductive success o Inrassexual selection  between members of the same species of the same sex (example: competition of males for females) o Intersexual selection  between sexes o o features are superficial  do not offer apparent benefits for survival o natural selection does not just apply to a species, but individually to each member of that species Evolution o at the level of individual organisms  organisms with adaptive traits survive longer and reproduce more (increases the number of organisms in a population over successive generation) o at the level of genes  frequency of alleles contributing to adaptive traits increases in a population o example: if animals of genotype AaBBCC and AABBCC lets say are more adaptive to environemtnal changes, over time that allele frequency of the population will increase i.e. there will be more and more individuals with that adaptive genotype Inclusive Fitness o why do animals show altruistic behaviors? 1 o Fitness = a measure of how many offspring an individual organism produces and supports o Inclusive fitness = the fitness of an individual plus part of the fitness of genetically related individuals o • Genetic diversity: allelic variation that can be acted on by natural selection to altruistic behavior (when an individual sacrifices its own life to protect the lives of kin, it is acting in the interest of its own genes) o Note- Critical for the survival of speciesd than kin selection in that it does not require genes that are identical by decent Genetic diversity greater the diversity of alleles in a species, the more likely the species can adapt o Genetic diversity: allelic variation that can be acted on by natural selection o Critical for the survival species o The greater the diversity of alleles in a species, the more likely the species can adapt to unpredictable environmental changes Gene7c+diversity+in+a+species+ “It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change.” - Charles Darwin Traits+(physical+or+behavioral)+diversity+in+a+species+ o Ability+to+cope+with+environmental+challenges+ o it is not the strongest of the species that survives, not the most intelligent , it is the one that is most adaptable to change  Charles Darwin o back to the hypothetical bird example  speciation is only possible when there is sufficient allele diversity Factors influencing genetic diversity o inbreeding (mating between genetically related individuals) o reduces heterozygosity and increase homozygosity o reduces genetic diversity o reduces viability (inbreeding depression) o example: Darwin married his fist cousin  3/10 kids died and a lot of the surviving 7 did not reproduce o gene flow: introducing new alleles through breeding with memebers of genetically different populations  in African monkeys – females rule they kick out the males and they have to go find another tribe to live and mate with  this inceases diversity of the different tribes o mutations (spontaneous or induced) o bad mutations are eliminated from populations o most of the time, the ones that remain increase diversibility and allow individuals to adapt to different environments o adaptability to stress is regulated by many genes, but they show plasticity through genetic variation in more than just humans  variation in these genes are conserved Nature of environmental effects o Postnatal environmental effect : parenting, physical illness, psychological stress, cultural experience, birth order o Prenatal environmental effect: nutrition, hormones, exposure to drugs, and toxins, maternal psychological stress Prenatal environments o Environmental effects on brain development o Natural Darwinism: during brain development, synapses that are most used are kept while the least used connections are destroyed or pruned to form neuronal circuits o Neurons that fail to establish active connections undergo apoptosis o Nutritional deficits or exposure to toxins can cause excessive and detrimental apoptosis thus abnormal behaviors later in postnatal life  exposure to heaby metals, nicotine, alcohol o Fetal alcohol sundrome  repeated exposure to alcohol during pregnancy o Endogenous hormones affect sex specific traits  bipotential state (gonads can develop into either female or male genital) o The developing fetus at early stage in pregnancy is largely bipotential  either develop testis or ovary 2 Prenatal environments (endogenous hormones affecting sex-specific traits) • Development of external genital organs :+Developing+fetus+at+early+stage+is+largely+bipoten7al.+ With+androgens+ Without+androgens+Sex+hormones+(e.g.+testosterone)+direct++ the+development+of+genital+organs:+ •In+the+presence+of+a+Y+chromosome,+testes+develop+in+ the+abdomen+and+begin+secre7ng+testosterone+and+ other+hormones,+then+direc7ng+development+of+male+ genitalia.+ •In+the+absence+of+Y+chromosome,+no+testosterone+and+ ovaries+develop+from+the+same+7ssue.+ o Male+genital+orgFemale+genital+organ+ Prenatal environments – Congential Adrenal Hyperplasia (CAH) o hyperplasia refers to enlargement due to increased cell division o secretion of abnormally high levels of adrenal hormones has testosterone-like effects on sex specific development o in XX individuals, characterized by external genital organ that is intermediate between male and female o fully functional ovaries and other reproductive organs o can supplement fetus with external glucocorticoids so that hyperplasia can be reduced by reducing the testosterone so that female genitalia can arise o most individuals like this tend to be lesbians  ethical issues in the gay community for the hormones that can be given to modify this Androgen Insesitivity Syndrome (AIS) – Prenatal environments o caused my mutations in the androgen receptor gene o mutated form of the receptor fails to bind testosterone o testosterone in XY individuals fails to direct the development of male genital organs o * partial AIS  external genital organs with features intermediate between male and female o * complete AIS  XY individuals develop genital organs that are indistinguishable from XX female o example: Maria Patino has complete AIS  she was banned from competing as a female hurdle (now no longer based on genotypic characteristics) Prenatal environments (continued) o the embryonic brain is sexually dimorphic structure o most sex specific behaviors seem to be established during fetal brain development o Medial Preoptic Area (MPOA)  located in the forebrain rostral (just at the base in front of ) the hypothalamus o Activity involved in male typical behavior  larger in males than females o Chemical lesion of MPOA in male rats abolishes male-typical behaviors o Female rats exposed to high level of testosterone during development show male typical behaviors Gene-Environment Interaction o Phenotype of a given genotype is determined by the environment o Environmental factors are main triggers for schizophrenia o Unclear whether it is the stressful environments that contributes to the alleles expression or the expression of those genes that causes the high stress 3 Gene –Environment interaction • Self reported depression symptoms compared between s/s, s/l, and l/l of 5-HTT promoter al
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