genetics and classification

• Genotype


  The set of alleles carried by an organism
• Phenotype


  An organism's observable features
• Alleles


  Different versions of a gene
• Dominant allele


  Hides a recessive allele and determines the organism's appearance
• Recessive allele


  Hidden by a dominant allele
• Homozygous


  Having two copies of the same allele
• Heterozygous


  Having two different copies of an allele
• Law of segregation


  Each gamete receives just one gene copy, which is selected randomly
• Punnett square


  • Used to predict genotypes and phenotypes of offspring from genetic crosses
• Test cross


  Used to determine whether an organism with a dominant phenotype is homozygous or heterozygous
• Homozygous recessive


  An organism that is homozygous for the recessive allele (e.g. green-seeded)
• Homozygous


  An organism that has two identical alleles for a particular trait
• Heterozygous


  An organism that has two different alleles for a particular trait
• Inheritance of dominant phenotype

  If the organism with the dominant phenotype is homozygous, then all the F1 offspring will get a dominant allele from that parent, be heterozygous, and show the dominant phenotype
• Inheritance of dominant and recessive phenotypes

  If the organism with the dominant phenotype is a heterozygote, the F1 offspring will be half heterozygotes (dominant phenotype) and half recessive homozygotes (recessive phenotype)
• The 1:1 ratio in the second case is another confirmation of Mendel's law of segregation
• Mendel's complete model also addressed whether genes for different characteristics (such as flower color and seed shape) influence each other's inheritance
• Mendel was able to figure out his entire model of inheritance simply from his observations of pea plants
• Qualities of a great scientist

  • Careful
  • Persistent
  • Curious
  • Thinking about results mathematically
• Dominant trait


  The trait that is visible in the offspring of a cross
• Recessive trait


  The trait that is hidden in the offspring of a cross
• Genotype


  Determines phenotype, but with influence from the environment
• Genotype


  The genetic makeup of an organism
• Phenotype


  The observable physical or biochemical characteristics of an organism
• Genotype and phenotype


  Both are influenced by the environment
• Genes mainly influence phenotype
• The environment also influences gene expression
• Phenotype relies on the degree of gene expression
• Homologous genes


  Genes controlling the same inherited character, may have different versions of the same gene
• Homozygous means the genes carry two identical alleles
• Heterozygous means the genes carry two different alleles
• Mendel's law of segregation


  Derived from monohybrid experiments
• If gametes can pass down both alleles, the possibility will be 1/16
• The possibility of 1/4 existing suggests that only 1 of the 2 alleles is passed down by the gamete
• Crossover between homologous chromosomes


  Can create new combinations of alleles (and sometimes even new alleles)
• If parents are one brown and one blue eyed, and the child is brown eyed, the child's child can have blue eyes if they marry a brown eyed person
• Self-fertilization in plants usually results in healthy offspring
• Pollination


  The transfer of pollen grains from the anther of one flower to the stigma of another flower
• Self-pollination


  Transfer of pollen grains of one flower to the stigma of the same flower
• Cross-pollination


  Transfer of pollen grains of one flower to the stigma of another flower