Heredity, Prenatal, and Birth

• Nature


  Heredity plays the most important role in bringing about a feature
• Nurture


  Environment is most significant in shaping the way we are
• Almost all human features

  • Polygenic - a result of many genes
  • Multifactorial - a result of many factors, both genetic and environmental
• • Genetic make-up sets up a range of possibilities
  • Genes may or may not be realized depending upon one's environmental experiences
• Environment affects the expression of genes

  Genetic predispositions can impact a person's potentials
• Environmental circumstances can trigger symptoms of a genetic disorder
• Heritability


  A statistic that represents the proportion of phenotypic variance that is due to genetic differences
• Estimates of heritability of intelligence are 80% (Bouchard et al., 1990) and 50% (Plomin 1990, 1995)
• Environment


  Plays a significant role in a person's mental ability, e.g. education, SES, nutrition, parents' behavior, alcohol use, criminal behavior, emotional adaptation, amount of time spent reading or even watching television (Flynn, 1992)
• • Genes are segments of chromosomes that vary in length
  • 46 strands of chemical substances called DNA are contained in the nucleus of each human cell
• Understanding the role of genes in health and illness can bring about both harm and good (Weitz, 2007)
• Monozygotic or identical twins


  Occur when a single zygote or fertilized egg splits apart in the first two weeks of development
• Dizygotic or fraternal twins


  Two eggs or ova, are released and fertilized by two separate sperm
• Genotypes


  The genetic complement, coded in DNA inherited from our parents
• Phenotypes


  Our observable characteristics
• Dominant genes


  Express themselves in the phenotype even when paired with a different version of the gene
• Recessive genes


  Express themselves only when paired with a similar version gene
• Incomplete dominance


  When a dominant gene does not entirely suppress the recessive gene
• Most characteristics are polygenic - not the result of a single gene, but of several genes
• Chromosomal abnormality


  Occurs when a child inherits too many or too few chromosomes
• • Most of the known genetic disorders are dominant gene-linked
  • Vast majority are not severe disorders
• Behavioral Genetics


  The scientific study of the interplay between genetic and environmental contributions to behavior
• Genotype-Environment Correlations


  Processes by which genetic factors contribute to variations in the environment
• Genotype-environment interactions


  • Involve genetic susceptibility to the environment
• Periods of Prenatal Development

  1. The Germinal Period

  2. The Embryonic Period

  3. The Fetal period
• • Prenatal development starts at conception
  • Zygote (fertilized egg) contains the combined genetic information from both parents
  • After five days of mitosis, there are 100 cells, which is now called a blastocyst
• • The embryonic period begins once the multi-cellular organism is implanted in uterine wall
  • The placenta is a structure connected to the uterus that provides nourishment and oxygen from mother to embryo via the umbilical cord
• Sex Linked chromosomal disorder: The disorder occurs on chromosome pair #23 or the sex chromosomes
• Turner syndrome is caused when all or part of one od the X chromosomes is lost before or soon after conception due to a random event
• klinefelter Syndrom is caused when an extra X chromosome is present in the cells of a male due to a random event.
• Huntington's Disease (heterozygous) is a condition that affects an individual's nervous system. The disease affects movement, behavior, and cognition
• Touretter syndrome (heterozygous) is a tic disorder which results in uncontrollable motor and vocal ticks as well as the body.
• Achondroplasia (heterozygous) fingersis the most common form of disproportionate short stature. Abnormal bone growth resulting in short stature, disproportionately short arms and legs, short finger, a large head, and specific facial features
• Genotype Environment Correlations

  refer to the processes by which genetic 

  factors contribute to variations in the 

  environment (Plomin, DeFries, Knopik, & 

  Niederhiser, 2013).
• After five days of mitosis, there are 100 cells, which is now called a blastocyst
• Cephalocaudal development from head to tail 
•  Proximodistal development from midline outward
• Teratology: a study of factors that contribute  to congenital disabilities
• Alcohol is one of the most commonly used teratogens, followed by Tobacco
• Genes are segments of chromosomes that vary in length