 Zygote: Union of sperm & ovum at conception  Contains 23 pairs of chromosomes  One pair from each parent  Each pair influences a characteristic  Chromosomes: thousands of genes containing DNA

 Meiosis: process producing sperm, ova  Mitosis: cell-division process creating all other cells throughout life

 Massive genome analysis projects  999/1000 human base chemicals: identical  1/1000 accounts for differences between us  Humans/Chimps share 96% genetic material  Gene variants evolved in recent centuries ◦ Adaptations to food sources, diseases,etc.  Findings also useful to identify genes associated with disease, drug treatments

 Monozygotic (MZ) twins: 100% related ◦ Single zygote divides ◦ 2 genetically identical individuals  Dizygotic (DZ) twins: 50% on average ◦ 2 ova fertilized by 2 sperm  Siblings: 50% on average  Parent & Child: 50% related, shared  Males: XY; Females: XX

 Genes: instructions for development ◦ Characteristics like eye color, height, IQ  Genotype: genetic makeup a person inherits (potential) e.g., genes for tallness  Phenotype: actual/expressed trait (height)  Regulator genes turn gene pairs on/off at different times ◦ Turned on for adolescent growth spurt ◦ Turned off in adulthood  Always influenced by environmental factors also

 Single gene-pair inheritance ◦ Dominant gene = dominant trait ◦ Recessive genes  Trait expressed if paired with a similar gene (Homozygous)  Trait not expressed if paired with dissimilar gene (Heterozygous) ◦ Recessive traits: homozygous recessive ◦ Dominant traits: hetero or homozygous gene pair

 About 9% affected in US ◦ Homozygous recessive  Heterozygous are “carriers” ◦ Can transmit gene to offspring ◦ If both parents carriers: 25% chance  Example of incomplete dominance ◦ Offspring may have sickling episodes

 Single genes located on sex chromosomes  Actually X-linked  Males - no counterpart on Y chromosome ◦ Only needs one to be color-blind  Females - counterpart on 2 nd X chromosome ◦ Usually for normal color-vision (dominant) ◦ Must inherit on both to be color-blind  Also Hemophilia, Duchene MS, others

 X-Linked Inheritance

 For most important human characteristics ◦ Height, intelligence, temperament, etc.  Trait influenced by multiple pairs of genes  These traits are normally distributed ◦ I.e., found in the same proportion in all populations

 A change in gene structure/arrangement  Produces a new phenotype  More likely in sperm than in ova  May be harmful or beneficial  Can be inherited by offspring

 Errors in chromosome division during meiosis ◦ Too many or too few chromosomes result ◦ Most spontaneously aborted

 Down Syndrome: Trisomy 21 ◦ Physical characteristics ◦ Mental retardation ◦ Related to age of both parents ◦ Often develop Alzheimer’s in middle age

 The rate of Down syndrome births increases steeply as the mother’s age increases.

 Turner’s syndrome: 1/3000 females ◦ Single X chromosome (XO) : small, unable to reproduce, stubby fingers, webbed neck

 Klinefelter syndrome: 1/200 males ◦ XXY: Sterility, feminine traits

 Fragile X syndrome: one arm on X is fragile (Leg of X barely connected) ◦ Usually males (sex-linked inheritance) ◦ Most common heredity cause of MR

 Helps people understand and adapt  Prenatal diagnosis: techniques include ◦ Amniocentisis, preimplantation  Human genome project yielded much info

 Tay-Sachs disease ◦ Cause: recessive gene pair (European Jews/French Canadians)  Huntington’s disease ◦ Deterioration of nervous system ◦ Single dominant gene ◦ One affected parent = 50% chance in offspring

 Genetic/environmental cause of traits  Heritibility estimates proportion of phenotypic variation in a population that is attributable to genetic variation among individuals. phenotypic variationgenetic variation  Experimental and selective breeding ◦ Tryon’s maze-bright rats  Twin, adoption, family studies ◦ Reared together or apart ◦ Concordance rates--twins are concordant if they both display a trait of interest

 Genetic similarity ◦ Degree of trait similarity  Shared environmental influence ◦ Living in the same home  Non-shared environmental influences ◦ Unique experiences  Genetic similarity ◦ Degree of trait similarity  Shared environmental influence ◦ Living in the same home  Non-shared environmental influences ◦ Unique experiences  Genetic similarity ◦ Degree of trait similarity  Shared environmental influence ◦ Living in the same home  Non-shared environmental influences ◦ Unique experiences

 Analysis of genes and their effects ◦ May compare humans with other animals  eg. Alzheimer’s disease ◦ Most common form of old age dementia ◦ Twin studies show heritability ◦ Possible genetic links being tested ◦ Environmental factors also being tested  High cholesterol, head injury

 Correlations highest in identical twins ◦ Genetic factors determine trait  Correlations higher if twins reared together ◦ Environmental factors ◦ Non-shared experiences influential  Identical twins more alike with age

 Temperament Correlations ◦ Identical twins =.50 to.60 ◦ Fraternal twins = 0 (even reared together!)  Personality Correlations Similar ◦ Shared environment unimportant ◦ Genetic inheritance important ◦ Non-shared experiences important for differences

 Correlations between the traits of identical twins raised apart in Minnesota Twin Study.

 Schizophrenia concordance rates ◦ ID twins: 48% ◦ Fraternal twins: 17% ◦ Affected parent increases risk even if adopted at birth  Inherited predisposition ◦ Environmental factors (triggers) ◦ Prenatal exposure to infection suspected