Vocabulary of Genetics

• characteristic
  any recognizable feature of an organism
• trait
  any inheritable characteristic
• expression
  description of the trait in a particular individual
• gene
  the genetic information controlling trait
  
• locus
  the physical location of a gene on a chromosome
• allele
  specific genetic information describing the expression of the trait
• phenotype
  list of the expression of all traits exhibited by an individual
• genotype
  list of the alleles for the trait in an individual
  usually as a set of code letters
• homozygous
  having matching alleles for a trait in an individual
  "pure-bred" in breeding vocabulary
• heterozygous
  have different alleles for a trait in an individual
  "hybrid" in breeding vocabulary
• dominance
  condition in which heterozygote individual resembles phenotype of one homozygote
  
  • dominant
    allele and associated phenotype of heterozygote and one homozygote
  • recessive
    non-dominant allele and associated phenotype
• analogous chromosomes
  any two (or more) chromosomes with same genes at same loci
• P-1
  the Parental generation
• F-1
  the 1^st Filial (brother) generation

Mendel

Mendel's Principles

Apply only to diploid species.
Mendel worked with garden peas.

• 1. each individual receives one allele for each trait from each parent
• 2. [therefore] each individual has two alleles for each trait
• 3. Alleles segregate independently during gamete formatioon [meiosis]
• 4. Alleles are paired during fertilization
• 5. (Some) expressions may mask the alternative expression [dominance]

the Monohybrid Cross

• a cross involving a single trait
• mating of F-1 individuals from the P-1 cross of two different pure bred lines

Dihybrid

• a cross involving two traits
• mating of F-1 individuals from the P-1 cross of two different pure bred lines

dihybrid, no dominance

dihybrid, with dominance

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