science reviewer (upexam) olfu scholar

• Mendelian genetics


  The study of how traits are passed on from one generation to the next
• Children look like their parents. Traits are passed on from generation to generation, be it hair color, skin tone, height, or anything else.
• For most of human history we had no idea how this happened, and even with the biology we have just learned, it still isn't entirely clear.
• Gregor Mendel


  The man who founded the field of genetics through his study of pea plants
• Mendel's background


  • Grew up poor in an agricultural area of Europe
  • Entered an Augustinian monastery at age 21
  • Left to study science in Vienna, then returned to the monastery eager to begin his research
• It was thought that heredity had to do with a blending of attributes, like the way two colors mix to give an intermediate color.
• This did not account for the way that traits can skip a generation.
• Gene theory


  Heredity is based on discrete units that can be inherited, which came to be referred to as genes
• Mendel worked for several decades with pea plants in the garden of his monastery to produce an impressive body of data to support the gene theory, all of which was done decades before chromosomes were observed and understood.
• Why Mendel chose pea plants

  • Pea plants have a number of visible traits that can vary, so results are easy to observe
  • Generations of the pea plant are short and the offspring are many, so data is easy to gather
  • Mendel could easily control mating by removing the stamens and deliberately cross-fertilizing with pollen from other plants
• True-breeding plants


  Plants that, when self-fertilizing, give generation after generation of the same phenotype
• Hybridization


  The process of breeding true-breeding plants with different traits
• Parental generation


  The two true-breeding plants used in a hybridization experiment
• F1 generation


  The offspring of the parental generation in a hybridization experiment
• F2 generation


  The offspring of the F1 generation in a hybridization experiment
• Phenotype


  The observable traits expressed by an organism
• Dominant trait


  A trait that is expressed in the phenotype even when only one copy of the gene is present
• Recessive trait


  A trait that is only expressed in the phenotype when two copies of the gene are present
• Allele


  One of the possible versions of a gene
• Genotype


  The genetic makeup of an organism, referring to the specific alleles present
• Homozygous


  Having two identical alleles for a particular gene
• Heterozygous


  Having two different alleles for a particular gene
• Mendel's laws of genetics

  • Law of segregation
  • Law of independent assortment
• Law of segregation


  1. Each gamete contains only one of the two alleles for a particular gene

  2. When the gametes fuse, the resulting organism has one allele from each parent
• Law of independent assortment

  1. The alleles for different genes segregate independently during gamete formation

  2. The combination of alleles in an organism is determined by probability
• Observing the phenotype


  Does not tell us with certainty what genotype is present, as multiple genotypes can result in the same phenotype
• Monohybrid cross


  Examining one trait at a time
• Dihybrid cross


  Examining two traits at the same time
• The phenotypic distribution for a dihybrid cross will always be 9 to 3 to 3 to 1.
• Not all patterns of inheritance are as simple as Mendel's experiments, and there are degrees of dominance, multiple alleles, and single genes producing multiple phenotypes.
• Incomplete dominance


  When the phenotype of the heterozygous genotype is intermediate between the two homozygous phenotypes
• Codominance


  When two different phenotypes are both expressed simultaneously
• Mendel's more advanced understanding of genetics required knowledge about chromosomes that he never had.