week 2

• Humans have trillions of cells and each cell has a core structure (nucleus) that contains 23 matching pairs of rod-shaped structures called chromosomes

  
• Chromosome


  One of 46 rodlike molecules that contain 23 pairs of tight strands of deoxyribonucleic acid (DNA)
• DNA


  Molecular structure inside cells that contains genetic information responsible for the development and function of an organism

  
• Gene


  The basic unit of heredity that occupies a specific location on a chromosome
• There are approximately 20,000 - 25,000 genes within our chromosomes
• Gamete


  An organism's reproductive cells (also known as sex cells)
• Female gametes


  Ova or egg cells
• Gametes


  Haploid cells as each cell carries only one copy of each chromosome
• Zygote


  A single celled organism resulting from a fertilized egg

  
• Traits and characteristics are inherited in predictable ways because outcomes can be explained by genetic inheritance
• Most humans have 23 pairs of chromosomes
• Alleles


  One of two or more different forms of the same gene at the same place on a chromosome
• Homozygous


  A chromosomal pair consisting of two identical alleles
• Heterozygous


  A chromosomal pair consisting of two different alleles
• Incomplete dominance


  Both genes are expressed in the phenotype
• Co-dominance


  Both alleles of a heterozygote lack the dominant and recessive relationship
• Polygenic inheritance


  Occurs when a trait is a function of inheritance of many genes, such as with height, intelligence, and temperament

  
• Genetic propensities interact with environmental influences to produce a wide range of differences across traits
• Many disorders and abnormalities are caused by inherited genes, some result from dominant-recessive inheritance where one or both parents contribute, and others are from chromosomal variation(s)
• Sex chromosome abnormalities


  Affect the number or the structure of the X and Y chromosomes
• Chromosomal abnormalities


  Occur as the result of errors during cell reproduction, meiosis, mitosis, or damage caused afterward
• Few severe disorders are inherited through dominant-recessive inheritance because if they were, the pregnancy would most likely end in miscarriage
• Mutation


  A sudden permanent change in the structure of genes that occurs spontaneously or may be inducted by exposure to environmental toxins
• Environmental factors that can cause mutations

  • Radiation, chemicals
• Genetic counselling


  Construct a family history of heritable disorders and perform blood tests to detect chromosomal abnormalities and/or dominant and recessive genes for various disorders (carrier screening)
• People who may be referred to genetic counsellors

  • Those with relatives with a genetic condition
  • Those having a hard time conceiving
  • Women over the age of 35
  • Couples from various ethnic groups
• Prenatal screening


  Provides information about the likelihood of a genetic or chromosome disorder (e.g., eFTS, NIPT)
• Prenatal testing


  Provides confirmation of a genetic or chromosome disorder (e.g., CVS, amnio.)
• Enhanced First-Trimester Screening (eFTS)

  Provides info about the chance of certain chromosomal differences, performed between 11w - 13w gestation, involves an NT ultrasound + blood work
• eFTS screen positive


  A higher than "normal" chance of the fetus having one of the conditions, does NOT mean fetus definitely has one of the conditions
• eFTS screen negative


  A lower than "normal" chance of the fetus having one of the conditions, does NOT mean fetus has a zero chance of having one of the conditions
• Non-Invasive Prenatal Testing (NIPT)


  Provides info about the chance of fetus having certain chromosome abnormalities, blood test to analyze cell-free DNA from maternal blood sample, performed at or after 9 weeks gestation, usually more accurate than eFTS
• Invasive diagnostic testing


  Optional testing that provides definitive answer about specific genetic and/or chromosome differences, typically offered if someone is screen positive/high-risk on prenatal screening or anatomical abnormalities are discovered on ultrasounds, small but serious risks (e.g., miscarriage)
• Chorionic Villus Sampling (CVS)

  Invasive diagnostic testing
• Amniocentesis (aka amnio)


  Invasive diagnostic testing
• Potential advantages and drawbacks of prenatal screening and prenatal testing
• Potential steps after prenatal diagnosis

  • Prenatal treatments (e.g., medications, fetal surgery)
  • Seeking support
  • Preparation for remainder of pregnancy
  • Preparation for birth
  • Preparation for newborn care
• Epigenetic framework


  A perspective that development results from reciprocal interactions between genetics and the environment such as the expression of genetic inheritance is influenced by environmental factors
• Niche-picking


  An active gene-environment correlation where people seek experiences and environments that complement their genes
• Teratogens


  Environmental factors that cause damage to prenatal development