Transcript Heredity, Prenatal Development and Birth

Heredity, Prenatal
Development and Birth
Chapter 2
Mechanism of Heredity
Egg & sperm each have 23 chromosomes
Contain genetic material (DNA)
Combine at conception into 23 pairs
23rd pair determines sex (XX XY)
Mechanism of Heredity
DNA consists of chemical compounds
organized into strings wrapped together
Adenine, thymine, guanine, cytosine
Order is unique for each individual
Cause cells to produce specific amino acids,
proteins & enzymes (building blocks)
A group of compounds providing set of biochemical
instructions = a gene (genotype) - 30,000 genes
Genes are functional unit of heredity & are the
basis for all human characteristics (phenotype)
Mechanism of Heredity
Genes come in different forms called alleles
2 alleles can be the same or different
Homozygous or heterozygous
Same: alleles produce the phenotype
Different: dominant allele produces phenotype
Some characteristics are caused by 1 gene
Blood type, vision, hearing, eye color
However some (psychological, behavioral) are rarely
due to a single gene
Behavioral Genetics
Study of inheritance of psychological and
behavioral characteristics
Not either or features (continuous range)
Most polygenic (multiple gene inheritance)
For example: perhaps 100 genes code for
extraversion (producing a range from low to high)
Difficult to determine specific genes involved
Can determine amount of population variance
due to genes (heritability)
Behavioral Genetics
Research Methods
Twin studies (MZ DZ)
MZ > DZ implicates genes
Adoption studies
Greater similarity among biological than adopted
relatives implicates genes > environment
Molecular genetics
Identify specific segments/alleles on genes
Determine which contribute to some characteristic
Heredity & Environment
Genotypes are set at conception
Phenotypes determined by genes &
environment
Genes determine likelihood of behavior
Which also depends on the environment
Musical genotype + athletic environment reduces
(p) of musical behavior
Reaction range: phenotype range limited by
genotype
Ultimate position determined by environment
Heredity & Environment
3 forms of interaction
1. Passive: parental genotype passes to child
along with early rearing environment
2. Evocative: children’s genotypes evoke
different reactions from environment
3. Active: people seek experiences
conforming to their genotype
Nature of Nurture
Genes make us similar
Non-shared environmental influences make
us different
Shared environmental influences only weakly
influence development
Siblings not much alike
Unique environmental experiences that are key
Siblings experience in same family very different
Influences on Prenatal
Development
Nutrition
Caloric intake increased by 10%-20%
25-35 lbs gained (fetus, placenta, fat stores)
Proteins, vitamins minerals key
• Folic acid key for nervous system (spina bifida)
Poor nutrition can lead to early, underweight birth
Increase risk for various developmental problems
Influences on Prenatal
Development
Stress
Primates: leads to small offspring prone to
various problems
Humans: associated w/ premature, small
birth
Stress hormones reduce flow of O2 to fetus
Stress weakens immune system
Increases tendency to smoke, poor eating or
exercise
• Prolonged, extreme stress
Influences on Prenatal
Development
Mother’s age
Teens, > 35 more problems (20-35 best)
20s 2x as fertile as women in 30s
> 35 risk for miscarriage increases
40-45 ~50% pregnancies end in miscarriage
Influences on Prenatal
Development
Teratogens: agent causing abnormal PD
Drugs
Nicotine: constricts blood vessels and
reduces O2 & nutrients to fetus
Miscarriage, small birth weight, impaired
attentional, language and cognitive skills,
behavioral problems
Alcohol: Fetal Alcohol Syndrome
Physical abnormalities, leading cause of mental
retardation in US, other problems common
Influences on Prenatal
Development
Diseases
Colds, flu no impact
Bacterial, viral infections can cause problems
Environmental Hazards
Lead, mercury, PCBs (even tiny amounts)
Teratogens: How
Impact depends on genotype
Not all species equally impacted
Exposure timing critical
Zygote: spontaneous abortion
Embryo: major defects in bodily structure
Fetus: body system lamfunction
Effects specific to the teratogen
Different body systems for different Teratogens
Teratogens: How
Dosage key
Damage may emerge later in life