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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