6.1.2 Patterns of inheritance

• What is a gene?


  A sequence of bases on a DNA molecule that codes for a protein.
• What does a gene code for?


  A protein (polypeptide) that results in a characteristic.
• What is an allele?


  A different version of a gene.
• How many alleles do most plants and animals have for each gene?


  Two alleles, one from each parent.
• How do the bases in different alleles compare?


  The order of bases in each allele is slightly different.
• How are alleles represented?


  Using letters, e.g., B for brown eyes and b for blue eyes.
• What is a genotype?


  The alleles an organism has, e.g., BB, Bb, or bb.
• What does the phenotype represent?


  The characteristics produced by the alleles.
• What is an example of a phenotype?


  Brown eyes.
• What is a dominant allele?


  An allele whose characteristic appears in the phenotype even with one copy.
• How is a dominant allele represented?


  By a capital letter.
• What is an example of a dominant allele?


  The allele for brown eyes (B).
• What is a recessive allele?


  An allele whose characteristic appears only if two copies are present.
• How is a recessive allele represented?


  By a lowercase letter.
• What is an example of a recessive allele?


  The allele for blue eyes (b).
• What are codominant alleles?


  Alleles that are both expressed in the phenotype.
• What is a locus?


  The fixed position of a gene on a chromosome.
• Where are alleles of a gene found?


  At the same locus on each chromosome in a pair.
• What is a homozygote?


  An organism that carries two copies of the same allele.
• What is an example of a homozygote?


  BB or bb.
• What is a heterozygote?


  An organism that carries two different alleles.
• What is an example of a heterozygote?


  Bb.
• What is a carrier?


  A person carrying an allele not expressed in the phenotype but can be passed to offspring.
• What are the key terms related to genetics covered in the study material?

  • Gene: Sequence of bases coding for a protein.
  • Allele: Different version of a gene.
  • Genotype: The alleles an organism has.
  • Phenotype: Characteristics produced by alleles.
  • Dominant: Allele expressed with one copy.
  • Recessive: Allele expressed with two copies.
  • Codominant: Both alleles expressed.
  • Locus: Fixed position of a gene on a chromosome.
  • Homozygote: Two copies of the same allele.
  • Heterozygote: Two different alleles.
  • Carrier: Person carrying an unexpressed allele.
• Genetic crosses

  1. parental phenotype in words
  2. parental genotype in letters
  3. parental gametes (in circles)
  4. genetic cross (punnett square)
  5. genotypes of offspring
  6. phenotypes of offspring (linked to genotypes)
  7. answer expressed correctly
• Answering genetic cross questions

  • probability - e.g. 3 in 4
  • ratio - e.g. 3:1
  • percentage - e.g. 75%