2 Notes: Genetics – biologicalpsych.com

Gregor Mendel (1822-1884)
- Augustinian monk
  - taught natural science
  - high school teacher
- Took long walks
  - found unusual ornamental plant
- Planted it
  - next to typical variety
  - grew progeny side by side
- Found
  - Offspring show essential traits of parents
  - Not influenced by environment
- Accomplishments
  - 1st to trace characteristics of successive generations of a living thing
  - 1st experimental study genetics
  - Way ahead of rest of science
  - 34 years before rediscovered
- Method
  - crossed & scored to thousand
  - over seven years
  - pea plants
- Findings
  - Traits inherited in certain ratios
  - Genes dominant or recessive
  - Factors are inherited intact
  - Each transmits only half its hereditary factors to its offspring
  - Different offspring, same parents receive diff sets of hereditary factors
Twins
- Select characteristic
- Compare to non-twins
- Fraternal twins
  - Different genetics
  - Same environment
- Identical twins
  - Same genetics
  - Same environment
- Adoption Studies
- Targeted Mutations
GENES AFFECT THREE THINGS
- 1. Blood-Brain Barrier
- 2. Genes affect behavior
  - No single gene causes any behavior
  - Multiple genes impact structures
- 3. Drug metabolism
  - Phase 1 = oxidation reactions
    - mediated by enzymes in liver
  - Phase 2 = combination (conjugations)
    - Caffeine
    - Fast acetylators (dominant)
    - Dominant gene
  - Fast processing:
    - into blood, out kidneys
    - 1-2 hours
  - Slow acetylators (recessive gene)
    - Impacts liver enzyme
    - Twice as long to process
      - more side effects
    - (2-4 hrs)
    - More drug in blood over time
    - Longer lasting effects
    - 50% in Whites and Blacks
    - 10% in Asians (and some Native Americans)
Dominant
- Single copy from either parent carries trait
- Heterozygous
  - Coded differently
- Recessive
  - Copy from each parent required
  - Can unknowingly carry disease
  - Can be hidden for generations
- Affected parent (Dad or Mum)
- All children have equal chance of inheritance
- Dominant-Recessive
  - Dominant Wins ¾ Times
    - Dominant Dominant
    - Dominant Recessive
    - Recessive Dominant
    - Recessive Recessive
  - Mendel’s peas
    - smooth or wrinkled
    - green or yellow
    - short or tall
Autosomal Traits
- Single gene on an autosome
  - (non-sex chromosome)
- Dominant Trait Examples:
  - Huntington’s disease
    - Neurological disease
    - Many copies of gene segment
  - Achondrophasia
    - Bone order disease that causes dwarfism
- Recessive Trait Examples:
  - Albinism
  - Cystic Fibrosis
  - Tay-Sachs disease
  - Sickle cell anemia
Affected parent (Dad or Mum)
- Children have 50% of inheriting one mutated allele
- Either get yours or spouse’s
- Makes you a carrier
  - One mutated allele
  - One normal allele
- Put two carriers together
  - 25% chance will transmit mutated gene
  - 1 will be unaffected
  - 2 will be carriers
  - 1 will be affected
- Get 2 good copies
- Get 1 good 1 bad
- Get 1 bad 1 good
- Get 2 bad copies
Sex-Linked Traits
- X-Chromosome Linked
- Females
  - Inherit X from mother
  - Inherit X from father’s mother
  - Healthy copy beats unhealthy (usually)
  - Problems in women only when both copies flawed
  - Rare
  - Have 1 bad copy = carrier
  - Have 2 bad copies = show trait
- Males
  - Most genes come in pairs
  - Except males
  - One Y chromosome
  - One X chromosome = from mother
  - Only one copy
  - No backup
- Coffin-Lowry Syndrome
  - Mutation in ribosomal protein gene
  - Mental retardation
  - Short stature
  - Craniofacial
  - Skeleton
X Inactivation
- Deactivates X chromosomes
  - Until only 1 active copy
  - Don’t want extra X proteins
  - Occurs during embryonic stage
  - If not go well…
- Triple-X Syndrome
  - Usually no major problems
  - XXX in some cells
  - Tall women
- Klinefelter’s Syndrome = XXY
  - Less facial & body hair
  - Less muscular
  - Larger breasts
  - Broader hips
  - Taller
Y-Linked Traits
- Only in men
- Traits passed from father to son
- Few genes on Y chromosome
- Male Pattern Baldness
  - Begins in front, move backward
    - M shape
    - Then become U-shaped
  - Current best guess
    - Susceptibility Y-linked
  - Can pass on to sons
    - Hair structure X-linked
Single Gene Disorders
- 4000+
- Cystic Fibrosis
- Hemophilia
- Sickle cell
Polygencic Disorders
- Complex & multifactorial
- Multiple genes in combination
- 10 genes involved in eye color
- Cluster in families
  - No clear pattern
  - Run in families
- Cluster in lifestyle & environment
- Examples
  - Multiple sclerosis, heart disease, diabetes, obesity
  - Mood disorders, hypertension, cleft palate
  - Asthma, cancer
Pedigree
- Ancestral relationship diagram
- Can identify:
  - autosomal dominant & recessive
  - x- & y-linked
- inbreeding = mating of closely related families
  - Royal families
Things We Inherit
- Hair growth pattern: left to right or right to left
- Widow’s peak vs straight hair line
- A & B blood type or O blood type
- Attached or unattached earlobe
- Straight vs hitchhiker’s thumb
- Roman vs non-prominent nose
- Straight vs crooked pinkies
- Nearsightedness vs normal
- Stright vs turned up nose
- Roll tongue in U or not
- Freckles vs no freckles
- Dimples vs no dimples
- High vs low heart rate
- Broad vs narrow nose
- Curly vs straight hair
- 5 or 6 fingers or toes
- Cleft vs smooth chin
- Large vs small eyes
- Migraines vs none

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