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 nearsightedness
normal vision night blindness
normal vision color blindness*
Hair dark hair blonde, light, red hair
non-red hair red hair
curly hair straight hair
full head of hair baldness*
widow’s peak normal hairline
*sex-linked characteristic
Examples of Dominant-Recessive Genes
Dominant Traits Recessive Traits
Facial features dimples no dimples
unattached earlobes attached earlobes
freckles no freckles
broad lips thin lips
Appendages extra digits normal number
fused digits normal digits
short digits normal digits
fingers lack 1 joint normal joints
limb dwarfing normal proportion
clubbed thumb normal thumb
double-jointedness normal joints
Examples of Dominant-Recessive Genes
Dominant Traits Recessive Traits
Other immunity to poison ivy susceptibility to poison ivy
normal pigmented skin albinism
normal blood clotting hemophilia*
normal hearing 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