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.

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

27. 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。

28. Questions?