DNA 2 - Key Terms

• Where are the chromosomes found in the cell?

  Nucleus 
• Alleles are the different versions of a particular gene.
• Our body cells contain two copies of each chromosome, one from our mother, and one from our father. This means that we also have two versions of each gene (each different version is a different allele). 
• Humans have two copies of each gene (alleles). If both alleles are the same, the person is said to be Homozygous for that gene.
• Alleles can be either dominant or recessive.
• Charlie is heterozygous with one dominant allele and one recessive allele.

  Which allele will be expressed? 

  The dominant allele
• In order to be expressed, how many recessive alleles must be present? 

  2
• 1. The term 'genotype' can be difficult to understand because it has multiple meanings.
  2. One definition describes a genotype as: 'an individual's collection of genes'.
  3. But the more common definition in this course is: 'the two alleles present for a particular gene'. 
  4. In either case, the term genotype refers to the specific genes or allele that an individual has.
• What is a phenotype?

  The characteristics an organism has as a result of their genotype
• If a mouse has one allele for brown fur, and another allele for black fur, would they be considered homozygous or heterozygous for that gene? 

  Heterozygous
• If the brown fur allele was dominant, and the black fur allele was recessive, what colour would the mouse be?

  Brown 

  
  

  So in summary, the genotype of the mouse is a brown fur allele and a black fur allele, whilst the phenotype is brown fur.