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Gene environment 2

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  • 1. The Human Heritage: Genes and the Environment Ching-fen Hsu 2013/9/27 Lecture 2
  • 2. Sexual Reproduction and Genetic Transmission • Sperm & egg: 23 chromosome • Chromosome: single molecule of DNA • DNA: long paired strands to create double helix • Four chemical bases in DNA: A/T/C/G • Sequences of bases: determine the info available • Gene: segments on chromosome/working subunit of DNA made up of bases/basic heredity unit • Ovum & sperm = zygote (46 chromosomes/ 23 pairs of chromosome)
  • 3. Process of Cell Replication • Mitosis: zygote creates new cells (1) 46 chromosomes move to the middle of the zygote (2) produce exact copies (3) chromosome separate into 2 identical sets (4) migrate to opposite sites (5) form two daughter cells with identical 23 pairs of chromosomes (6) daughter cells create new cells repeatedly • Life long process: create new body cells for replacing old • Genetic material is not altered in life
  • 4. Source of Genetic Variation • Meiosis: cell division process • Germ cell replication: sperm & ova • Make sure zygote with 46 chromos • Initial stage of genetic lottery • Genetic diversity: newly conceived individual differs from both mother & father Meiosis in the Male Meiosis in the Female • Monozygotic twins: a single fertilized egg with identical genetic info. 1:250, never exactly alike with differences in environment • Dizygotic twins • 8 million (223) possible genetic combinations for each sperm & ovum • 1 in 64 trillion chance for exactly the same genes
  • 5. Sexual Determination • Another source of variation • Human differs at 23rd chromosome • Females: XX • Males: XY • Y chromosome is smaller than X X chromo Y chromo
  • 6. Genotype & Phenotype • How genes influence development • Genotype: individual’s genetic endowment; particular gene forms that individual inherits; constant over lifetime • Phenotype: observable characteristics/ traits on physical, psychological, healthy, behavioral levels; interaction with E • Genetic inheritance expresses itself through interaction with E to create phenotype
  • 7. Genotype
  • 8. Laws of Genetic Inheritance • Scientific understanding of gene transmission across generations • Characters pass-on • Genes contribute particular inherited characteristics • Allele: specific form (trait) of a gene • Homozygous: same allele forms of the corresponding genes (cleft vs. non-cleft) • Heterozygous: different allele forms, important in understanding genotypic combinations for producing different phenotypes Gregor Mendel 1822-1884
  • 9. Knowing Inheritance • Dominant allele: expressed characteristic-carrying allele • Recessive allele: unexpressed allele • Intermediate bet two alleles: affected by 2 alleles, skin color • Codominance: affected by 2 alleles/ totally different from both • Polygenic trait: >2 genes in complex beh traits (verbal skills)
  • 10. Sex-Linked Genetic Effects • Sex-linked characteristics: specific inherited deficit with X/Y chromosome • Mostly X-chromo related (girls from each parent; boy from mother) • Females: complementary function from the other X-chromo • Males: fragile function on X-chromo/getting deficits e.g., red-green color blindness (lack of color-absorbing pigments in the retina of the eye) girls: homozygous alleles from both parents boys: inherited from mothers hemophilia/muscular dystrophy
  • 11. Phenotype
  • 12. Gene-Environment Interaction • Cell: interactive environment for genes (amio acid sequences of proteins produced by cells) • Behavioral genetics: understand how G & E factors combine to produce individual differences in behavior • Principle#1: interaction be studied under a broad & ecological framework (parents’ interaction on children’s temper studies) • Principle#2: two-way process of G vs. E (irritable infants in Brazil) • Principle#3: G factors determine inhabited E & individuals shape/ select E (high stimulation)
  • 13. Range of Reaction • Two approaches in study GE interaction (1) Keep E constant: G influences (2) Keep G constant: E influences • Range of reaction: changes of E of a particular G = phenotype e.g., Himalayan rabbits fur color vs. temperature bet 2 extremes: dark --- white fur • Ethnical problem on human studies • Should be cautious on explanations of animal studies
  • 14. Genetic Influences on Human Behavior
  • 15. Heritability• Individual differences = Gs + Es interaction • G/ Gs ≠ a certain behavior • Heritability == statistical correlation proportion of phenotypic variation in a population that is attributable to genetic variation among individuals estimate relative contributions of differences in genetic and non-genetic factors to the total phenotypic variance in a population Heritability coefficient h2 == genetic variation == population statistics e.g., 90% height variation from genes in the US • Explanation of heritability including E factor e.g., IQ score increases in the US 16-20y (the young leave home then) • Discrete gene = responsible for particular phenotype in E e.g., WS
  • 16. KE Family • Since 1990 in London • 30 family members suffer specific language impairment • Have problem controlling lower half of face in speech • Have difficulty writing down as many words as possible with the beginning of a certain letter • Chromosome 7 gene FOXP2 • Nucleotide 7q31 mutation • Uncertainty about E (education, developmental course, disease history)
  • 17. Kinship Studies • Naturally occurring conditions by kinship relationships to estimate G & E contributions to a phenotype • Design#1: family study---relatives(live together) are compared in a family to determine how similar they are on a trait • Design#2: twin study---groups of MZ & DZ twins of same sex are compared to each other & to other family members for similarity on a trait Design#3: Adoption study---G-related relatives are raised in different Es/ G-unrelated individuals in same E are compared for knowing if G/ E controls a trait Sociability, liveliness, impulsiveness
  • 18. Mutations & Genetic Abnormalities• Gene pool: the total variety of genetic info possessed by a sexually reproducing population • Mutation: error in the process of gene replication that results in a change in molecular structure of the DNA • Causes: only part of chromosome is replicated a part is lost on a particular gene / sequence of genes • Somatic (body) cell affects the carrying person only • Genetic defect affects generations • Mutation creates new genes in the gene pool • A small change in human genes leads to serious problems
  • 19. Interests in Genetic Abnormality Studies • ½ human conceptions have chromosomal abnormality • Majority of abnormalities results in miscarriage • 3.5% babies born with genotypic aberration (recessive) • Reason#1: understand mutation reveal interaction of heredity & E • Reason#2: find ways to prevent/ameliorate birth defeats • Reason#3: try to reduce impact of abnormalities on children & families
  • 20. Down Syndrome • First human disease linked with specific chromosomal disorder • >95% DS are trisomy chromosome 21 • Mental & physical retardation: slanting eyes, fold on eyelids, flat facial profile, ears lower than normal, short neck, protruding tongue, dental irregularity, short broad hands, small curved fingers • Heart, ear, eye problems, likely to die young • 1:1000 etiology; >30y pregnancy, 1:800; >40y, 1:100; >45y, 1:32; >49y, 1:12 • Women’s potential eggs are affected by E chemicals, radiation, viruses
  • 21. Phenylketonuria• Inherited metabolic disorder leads to severe mental retardation • Caused by a defective recessive gene that reduces body’s ability to covert one amino acid (phenylalanine) into another (tyrosine) • PKU children produce too much phenylalanine in bloodstreams which retards development of brain cells in prefrontal cortex • US 1:10,000 PKU; Europe 1:100 • PKU incidence is lower among blacks than whites • Feeding PKU infants diet low in phenylalanine (milk, egg, bread, fish) reduces severity of mental retardation compared to untreated infants • PKU infants will suffer brain irreversible damage in 1-3 months
  • 22. Sickle-Cell Anemia • People who inherit the recessive gene for sickle-cell trait from both of their parents & homozygous suffer from serious abnormality of red blood cells • Sickle-cell anemia take on curved sickle shape when oxygen supply to blood is reduced • Abnormal blood cells clump together & clog body’s blood vessels for people to have pain • This disease enlarges the heart & deprives the brain of blood • Deformed blood cells rupture easily & may lead to death • Africans (20%): Americans (8-9%)
  • 23. Before Marriage Health Check 婚前健康檢查 • Going-to-marry couple/ going-to-have-baby couple • 傳染性疾病(病毒性肝炎/ 愛滋病/ 梅毒) • 遺傳疾病篩檢(地中海型貧血/ 蠶豆症) • 生育健康諮詢 產前遺傳診斷 • 超音波掃瞄羊膜穿刺術/ 絨毛取樣/ 胎兒臍帶抽血術 羊膜穿刺術 • 16-18週發現胎兒染色體異常基因疾病 • 抽取約20cc羊水檢驗室做細胞培養/ 胎兒染色體檢查 • 3-week process • 胎兒染色體分析: 可檢查染色數目或構造是否正常 胎兒蛋白定量檢查: 檢查胎兒是否有開放性神經管缺損 單基因疾病檢查: 例如海洋性貧血
  • 24. Cultural Evolution • Phenotypes acquired in lifetimes can be transmitted to next generations parents pass on criminality to children marking  writing/ numerical calculation • Successful innovations of earlier generations pass on knowledge through language + instruction • Meme: basic unit of cultural inheritance carry knowledge (how to study an exam) evolve & transmit through social processes over time Quechan people in Andes Mountains of Peru
  • 25. Coevolution & Survival Strategy • Coevoltion: combined process emerges from interaction of biological & cultural evolution • Development sequence: biological maturation  cultural generation • 3 million years ago: primary cultural tools • Modern people’s brain (frontal lobe) 3 times larger
  • 26. Teaching Implications 許靜芬。2010。父母是 孩子的祝福,不是咒詛。 蒙特梭利雙月刊,91期, 教育園丁專欄,第6頁。
  • 27. Questions?