Gene environment 2
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This document summarizes a lecture on human genetics and heredity. It discusses key topics like sexual reproduction, genetic transmission through DNA, cell replication, genetic variation through meiosis and recombination, sex determination, the relationship between genotypes and phenotypes, Mendel's laws of inheritance, sex-linked traits, the interaction between genes and the environment, heritability, genetic influences on behavior through family and twin studies, genetic mutations and abnormalities like Down syndrome, phenylketonuria, and sickle cell anemia. Cultural evolution and gene-culture coevolution are also briefly covered.
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Gene environment 2
- 1. The Human Heritage: Genes and the Environment Ching-fen Hsu 2013/9/27 Lecture 2
- 3. 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)
- 4. 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
- 5. 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
- 6. 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
- 7. 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
- 8. Genotype
- 9. 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
- 10. 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)
- 11. 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
- 12. Phenotype
- 13. 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)
- 14. 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
- 15. Genetic Influences on Human Behavior
- 16. 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
- 17. 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)
- 18. 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
- 19. 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
- 20. 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
- 21. 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
- 22. 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
- 23. 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%)
- 24. 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
- 25. 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
- 26. 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
- 28. Questions?