Mendelian genetics terminology

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• Mendelian genetics terminology

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Alleles

• These are alternate forms of genes
• A dominant allele is a hereditary trait that is
  always expressed or seen in the offspring.
• Capital letters are used to represent a dominant
  allele.
• For example T for tall

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• A recessive allele is a hereditary factor that is
  not usually expressed in an individual.
• A lowercase letter is used to represent the
  allele.
• For example t for short

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The alleles for a single gene can have three
combinations in a pair of homologous chromosomes.

• Homozygous dominant is represented by the
  genotype TT
• Homozygous recessive is represented by the
  genotype tt
• Note Both are considered to be pure breeding
  individuals.

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• 3. Heterozygotes are represented by the genotype
  Tt.
• Heterozygotes will express or show the dominant
  allele as the recessive allele is inactive.

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A genotype is the genetic makeup of an organism
due to the alleles present in the genes. Ex. Tt,
TT, ttA phenotype is a particular physical
appearance produced by the alleles in a gene. Ex.
Tall or short
Phenotype and Genotype
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Mendels observations

• Mendel found
• 1- Each parent contributes one allele during
  cross fertilization. If a pure-breeding plant
  self fertilizes, each offspring receives
  identical copies of the same allele.
• 2- Dominant alleles are always expressed when the
  recessive allele is present.
• 3- Each pair of alleles segregates during the
  formation of sex cells.

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PARENT and FILIAL GENERATIONS

• The first generation is always called the parent
  or P1 GENERATION.
• The offspring of the P1 generation are called the
  first filial or F1 generation.
• The offspring of the F1 generation are called the
  F2 generation or second filial generation.