Genetic Inheritance Conception The union of sperm and ovum create a zygote The zygote contains a complete set of 46 chromosomes The first 22 pairs are called autosomes. The 23rd pair are the sex chromosomes. DNA Genes

Genetic Principles Genes Genotype. Phenotype Reaction range Alleles Homozygous Alleles (similar) Heterozygous Alleles (different) dominant - recessive gene principle incomplete dominance (blending) codominance (type AB blood)

Genetic Inheritance Single Gene-Pair Inheritance Polygenetic Inheritance Genetic Imprinting Genes are (chemically marked) in one of the parents and have different effects depending on which parent carries it. Huntington disease manifests earlier if passed on by the male Asthma / females , Diabetes / males

Genetic Inheritance Sex Linked Genes or Traits (X-linked inheritance) ex: hemophilia, red/green color blindness Mutations A sudden, permanent alteration in DNA occurs spontaneously or by environmental hazards Chromosomal Abnormalities Often the result of the 46 chromosomes not being divided equally (too many or too few) Down Syndrome

Genetics & Environment Heritability: The amount of variability in a population on some trait dimension that is attributable to genetic differences among those individuals

Gene-Environment Relationships Epigenetic View: Heredity  Environment Passive Gene-Environment Relation Evocative Gene-Environment Relation Active Gene-Environment Relation Shared and Non-shared Experiences

Stages of Prenatal Development

Germinal Stage (Weeks 1-2) The zygote, begins to divide, and travels down the fallopian tube. The new cells form the blastocyst, which attaches itself to the uterine wall The blastocyst forms several layers of cells The outer cells (trophoblast) form the placenta.

Embryonic Stage (weeks 3 – 8) The inner cells of the blastocyst which will become the embryo differentiate into three layers: Ectoderm: Outermost layer which will become skin, hair, nails, the nervous system, and sensory receptors Mesoderm: Middle layer which will develop into the circulatory system, bones, muscles, excretory and reproductive system Endoderm: Undermost layer which will develop into the digestive and respiratory systems

Embryonic Stage (weeks 3 – 8) The formation of organs begins (organogenesis) Sexual differentiation takes place around the 7th or 8th week By the end of the embryonic stage about 95% of body parts and systems have begun development.

Fetal Stage (Week 9-Birth) This period involves the dramatic increase in body size and completion of all physical structures Age of viability = approx. week 25

Prenatal Growth Occurs in three patterns: Orthogenic Cells are all the same and then differentiate Cephalocaudal: Latin for “from head to tail”. Proximodistal: Latin for “from near to far”.

Influences on Prenatal Development Nutrition Stress Mother’s Emotional state Mother’s Age Nearly 50% of pregnancies among women in their 40’s and 50’s result in miscarriage. Father

Influences on Prenatal Development Teratogans are any disease, drugs, or other environmental agents that can cause damage to a developing fetus. Effects depend on: Dose Heredity Presence of other teratogens Age of child Sensitive period

Postnatal (Postpartum) Depression Occurs in 1/10 new mothers Effects bonding and initial care of child Effects on mother May not want child Mood lability and other symptoms of depression Psychosis SI / HI

Postnatal (Postpartum) Depression Effects on child Susceptibility Past episode(s) of post partum (30 to 50% chance with each subsequent delivery) Personal past history of a mood disorder Family history of Bipolar disorder (even if not personally experienced)