Genetics 101

• Law of segregation

  The alleles present in each diploid parent segregate independently
• Result of the law of segregation

  Offspring receives one allele from each parent
• Monohybrid cross

  A breeding experiment in which the parents differ in one characteristic
• Ratio of phenotypes for a monohybrid cross with 2 heterozygous parents

  3:1 Dominant phenotype : Recessive phenotype)
• True-breeding individual

  An individual which is homozygous
• Homozygous alleles

  Alleles which are the same
• Heterozygous alleles

  Alleles which are different
• Test cross

  Used to determine the genotype of a dominant phenotype
• How a test cross is done

  Homozygous recessive is crossed with a dominant phenotype
• Mendel's law of independent assortment

  Each pair of alleles assorts independently of each other in gamete formation
• Dihybrid cross

  When the parents differ in two characteristics
• Ratio of F2 generation for a dihybrid cross of two true-breeding parents

  9:3:3:1 (HD:H:H:HR)
• Recombinant phenotype

  A phenotype which differs from the parents
• Trihybrid cross

  When the parents differ in 3 characteristics
• Allele

  A different form of a gene for a specific phenotype
• Phenotype

  The visible characteristics
• Homologous pairs of chromosomes

  Chromosomes are inherited from each parent with different alleles at the same loci
• Sister chromatids

  2 Identical chromatids held at the centromere
• Chromatids

  Identical strands are produced from the replication of a homologous pair of chromosomes
• Chromosome theory of inheritance

  Genes are located at specific loci on chromosomes. And so it is the chromosomes which express the features of Mendel's laws
• what is a self-cross

  when a genotype is crossed with itself