Gene environment 2

The Human Heritage: Genes and the Environment

Ching-fen Hsu

2013/9/27

Lecture 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)

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

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

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

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

Genotype

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

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)

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

Phenotype

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)

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

Genetic Influences on Human Behavior

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

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)

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

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

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

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

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

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%)

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

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

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

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。

Questions?