gene environment 2
TRANSCRIPT
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The Human Heritage: Genes and the Environment
Ching-fen Hsu
2013/9/27
Lecture 2
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Sexual Reproduction and Genetic Transmission
• Sperm & egg: 23
chromosomes
• 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)
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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 ones
• Genetic material is not altered in life
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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
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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
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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
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Genotype
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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
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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)
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Sex-Linked Genetic Effects
• Sex-linked characteristics: specific inherited deficit with X/Y
chromosome
• Mostly X-chromo related (girls from each parent; boys 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 mother
hemophilia/muscular dystrophy
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Phenotype
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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)
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Building Blocks of the Nervous System: Neurons
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Neural Basis for Learning • Learning involves changes in how
neurons function internally and in
their communication with each other
• Learning depends on neural
plasticity: capacity for neurons to
change with experience
• Long-term potentiation (LTP): (1)
neural basis for memory (2)
plausible mechanism for supporting
learning across species
• Potentiation effect (neuron A, C)
• Activity-dependent spread
potentiation (neuron A, B, C)
• LTP: cellular mechanism via
associations in the brain
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Learning: Structural Changes
• Key form in learning in mammals
other than presynaptic facilitation &
LTP
• Creation of entirely new synapses
• Changes take place on the dendrites
• Dendritic spines grow
• More spines = gaining more new
synapses = creating more new lines
of communication with cellular
neighbors
• Species diff in how they learn with
much in common (presynaptic
facilitation vs. dendritic spines)
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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
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Genetic Influences on Human Behavior
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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
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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)
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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
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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
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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
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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
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Phenylketonuria • Inherited metabolic disorder leads to severe
mental retardation
• Caused by a defective recessive gene that reduces body’s ability to convert 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
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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%)
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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: 可檢查染色體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
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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
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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
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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。
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Questions?