Download Theories of Human Development

Hereditary Influences on
Development
Chapter 3
The Genetic Code

Chromosomes
– Rodlike
– Store and transmit genetic information
– Matching pairs
– 46 chromosomes, 23 pairs…

Comprised of deoxyribonucleic acid, DNA
Gametes/Sex Cells
Sperm, ovum
 Contain only 23 chromosomes
 Formed through meiosis
 “Regular” body cells  mitosis
 Sex cells  meiosis
 Crossing over

Multiple Offspring
Identical/monozygotic twins
 Fraternal/dizygotic twins

Patterns of Genetic Influence
Phenotype
 Genotype
 Can have same phenotype but different
genotypes…why?

How Are Genes Expressed?

Simple dominant-recessive inheritance
– Each different form of a gene is called an
allele
– Alleles alike = homozygous
Alleles different = heterozygous
How Are Genes Expressed?

Dominant-recessive
Examples of Dominant-Recessive Genes
Dominant Traits
Recessive Traits
Eye color
brown eyes
grey, green, hazel, blue
Vision
farsightedness
normal vision
normal vision
normal vision
normal vision
nearsightedness
night blindness
color blindness*
Hair
dark hair
non-red hair
curly hair
full head of hair
widow’s peak
blonde, light, red hair
red hair
straight hair
baldness*
normal hairline
*sex-linked characteristic
Examples of Dominant-Recessive Genes
Dominant Traits
Recessive Traits
Facial features
dimples
unattached earlobes
freckles
broad lips
no dimples
attached earlobes
no freckles
thin lips
Appendages
extra digits
fused digits
short digits
fingers lack 1 joint
limb dwarfing
clubbed thumb
double-jointedness
normal
normal
normal
normal
normal
normal
normal
number
digits
digits
joints
proportion
thumb
joints
Examples of Dominant-Recessive Genes
Dominant Traits
Other
immunity to poison ivy
normal pigmented skin
normal blood clotting
normal hearing
Recessive Traits
susceptibility to poison ivy
albinism
hemophilia*
congenital deafness
normal hearing and speaking deaf mutism
normal – no PKU
phenylketonuria (PKU)
*sex-linked characteristic
How Are Genes Expressed?

If heterozygous, can pass on a recessive
allele to children
– Carriers

Phenylketonuria (PKU)
How Are Genes Expressed?
Sex-linked inheritance
 Codominance
 Polygenic inheritance

Hereditary Disorders

Chromosomal abnormalities
Hereditary Disorders

Autosomal abnormalities
– Most frequent is Down syndrome (trisomy 21)
– Mental retardation
– Distinctive physical features

Mutations
Detecting Hereditary Disorders
Amniocentesis
 Chorionic villus sampling
 Ultrasound


Know the procedures, advantages, and
disadvantages of each…
Genetic-Environmental Interactions

Reaction range
Range of Reaction
Canalization
Heredity restricts development of some
characteristics
 Examples = babbling, motor development

Behavioral Genetics
The scientific study of how genotype
interacts with the environment to
determine behavioral attributes such as
intelligence, personality, and mental health
 Methods of studying hereditary influences

– Selective breeding
– Family studies
 Twin studies
 Adoption studies
Behavioral Genetics

Twin studies
– Identical/fraternal reared together
– Adoption studies
– Identical twins reared apart
Calculate concordance rates
 Heritability coefficient

Behavioral Genetics
Heritability coefficient (H) = (r identical –
r fraternal) X 2
 Environmental influences

– Nonshared environmental influences (NSE)
 1 – r identical twins reared together
– Shared environment influences
 1 - (H + NSE)
Behavioral Genetics

Anxiety scale score
– Monozygotic twins: r = .78
– Dizygotic twins: r = .51
– Heritability:
 2(.78-.51)
 2(.27)
 .54
– Nonshared:
 1 - .78 = .22
– Shared:
 1 – (.54 + .22)
 1 - .76 = .24
Behavioral Genetics

Favorite color
– Monozygotic twins: r = .26
– Dizygotic twins: r = .23
– Heritability:
 2(.26-.23)
 2(.03)
 .06
– Nonshared:
 1 - .26 = .74
– Shared:
 1 – (.06 + .74)
 1 - .80 = .20
Molecular Genetics
To discover the precise locations of genes
that determine an individual’s
susceptibility to various diseases and other
aspects of health and well-being
 Genome = complete set of instructions for
making an organism
 Human Genome Project
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