GENETIC BASES OF DEVELOPMENT Heredity and Chromosomes Each egg and each sperm contain 23 chromosomes Fertilization sperm and egg combine Embryo has 46 chromosomes Defines the child s heredity Including sex and other physical traits Chromosomal abnormalities Down Syndrome instead of 2 Trisomy 21 An extra copy of chromosome 21 have 3 Facial deformities delayed motor and mental abilities Increased risk with age of mother Klinefelter syndrome Males have extra x chromosome XXY instead of XY Undeveloped testes and some feminine features including breasts Fragile X syndrome Damaged X chromosome Delayed or reduced mental abilities Chromosomal abnormalities Turner syndrome Females missing one of the X chromosomes Some physical deformity infertility and some mental retardation XYY syndrome Males with an extra Y chromosome Slight increases in physical growth rate Slight delays in language development What genes do Regulate protein production Building blocks of all cells tissue in the body Genotype a person s genetic makeup Phenotype a person s actual features Dominant vs Recessive genes Individuals not the sole product of their genes Epigenetics complex interactions between genes and environment Epigenetics Passive genotype environment interaction Biological parents provide the rearing environment Example Parents provide a genetic basis for intelligence as well as encouraging intellectual development Evocative genotype environment interaction Child s genotype elicits particular environments Example Smiling babies elicits more social interaction reinforcing extrovert behavior Active genotype environment interaction Niche picking Example Good sensorimotor skills may lead child to play sports in turn improves sensorimotor skills What is inherited Physical traits Height weight hair color skin color eye color blood type many misc physical features Environment still plays a role in phenotype of these traits e g nutrition diet genes height weight Psychological traits Behavioral Genetics study of the contributions of genes and environment to psychological traits Classic Nature vs Nurture debate Which dominates Answer It depends Or both to varying degrees depending on context Example Intelligence Family resemblance is insufficient to say its all genes E g Parents are intelligent so are children so does it mean IQ is inherited Environment could just as likely have caused intelligence Intelligent parents encouraged children to read sent them to good schools valued education etc Twin studies Twins Monozygotic identical twins Exact same genotype Dizygotic fraternal twins non identical Different genotype Compare psych similarities between monozygotic and dizygotic twins Twins experience same environment Only difference is genotype If monozygotic twins are more similar e g exhibit same intelligence then the genotype must play a strong role in the trait If dizygotic twins are just as similar e g same intelligence as monozygotic twins environment must be the factor Example Extroversion Dizygotic twins T1 T2 Fam A 80 95 Fam B 70 50 Fam C 10 35 Fam D 25 5 Fam E 40 65 Monozygotic twins T1 T2 Fam F 100 95 Fam G 32 30 Fam H 18 15 Fam I 55 60 Fam J 70 62 General similarity between dizygotic twins Even more similarity between monozygotic twins Evidence that extroversion is inherited Example Depression If one twin is depressed 75 chance the Identical twins other one will be Fraternal twins If one twin is depressed 25 chance the other one will be Suggests genetic basis of depression Adoption studies Children raised by adoptive parents If the children share psych traits with biological parents genetic basis for these traits Monozygotic twins raised in separate households If still similar wrt psych traits genetic basis for these traits Conversely if adopted children are more like their adoptive parents environmental basis for these traits Example Extroversion Child Child s Score Bio Moth Score Adopt Moth Score A 60 70 35 B 45 50 25 C 40 30 80 D 90 80 50 E 25 5 55 Average diff between child and biological mother 9 points Average diff between child and adoptive mother 29 points Evidence for genetic basis of extroversion Case studies Separated at birth Jim and Jim twins Separated at 4 weeks reunited at age 39 Similarities Were part time deputy sheriffs Vacationed in Florida Married and divorced women named Betty Had dogs named Toy Enjoyed carpentry and mechanical drawing Chewed fingernails Had sons named James Allan and James Alan Began suffering headaches at age 18 Case studies Separated at birth Two female identical twins Separated at 6 weeks Reunited in their fifties Similarities Identical nightmares began in early teens Imagery of doorknobs and fishhooks in their mouths and smothering Bed wetters until age 12 13 PRENATAL DEVELOPMENT Conception Sperm 23 chromosomes Egg 23 chromosomes Fertilization occurs in Fallopian tube The Germinal Period 1st 2 weeks Aka period of the Zygote Zygote fertilized egg Initially single cell Repeated processes of cell division of cells increases at exponential rate Monozygotic twins can occur at this stage Cells are all identical early in germinal period Fertilization and zygote Germinal period Germinal period ends with zygote embedding into uterine wall Connection with mother s blood supply Takes 4 8 days to complete the process Zygote has 60 70 cells First stages of cell differentiation begin Monozygotic twins cannot occur Forms a hollow spherical shape called blastocyst Inner layer of cells embryonic disk Becomes the developing child Outer layer of cells trophoblast Develops into the placenta and other protective tissues Hormonal changes occur Stops menstruation Prevents mother s immune system from rejecting blastocyst Most pregnancy tests will test positive at this stage Embryonic stage 3 8 Weeks Aka Period of the Embryo Cells becoming more specialized or differentiated During this stage Body structures Internal organs Embryonic stage 3 8 Weeks Beginning of embryonic stage Three layers form in the embryo Ectoderm outer layer Will become hair skin nervous system Mesoderm middle layer Will be muscles bones circulatory system Endoderm Digestive system lungs Cephalocaudal principle Head develops before rest of body More rapidly Early stages head is 50 of body length About 3rd 4th week At birth head is 30 of body length Ectoderm Early in 3rd week Fold appears in ectoderm Neural tube Will become CNS Neural Tube Mantle layer source of differentiating cells Cells will become important parts