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
Hair
*sex-linked characteristic dark hair non-red hair curly hair full head of hair widow’s peak normal vision nearsightedness night blindness color blindness* blonde, light, red hair red hair straight hair baldness* normal hairline

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 number normal digits normal digits normal joints normal proportion normal thumb normal joints

Other
Examples of Dominant-Recessive Genes
Dominant Traits Recessive Traits immunity to poison ivy susceptibility to poison ivy normal pigmented skin albinism normal blood clotting normal hearing 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