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
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
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
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%)
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
