Alleles, Dominant, Heterozygous, Phenotypes etc.

• Where are chromosomes found in the cell?

  Nucleus
• Alleles are the different version of a particular gene.
• Our body cells contain 2 copies of each chromosome, one from mother, one from father. This means we also have 2 versions of each gene. (each different version is a different allele).
• Alleles are?


  Different versions of the same gene.
• Humans have 2 copies of each gene. If both alleles are the same, the person is said to be homozygous for that gene.
• Homozygous is..


  Alleles are both identical for the same characteristic.
• Heterozygous is..


  Alleles are different for the same characteristic.
• Alleles can either be dominant or recessive.
• A mouse is heterozygous with one dominant allele and one recessive allele. Which allele will be expressed?

  Dominant
• In order to be expressed, how many recessive alleles must be present?

  2
• Genotype


  The two alleles present for a particular gene.
• Phenotype


  The physical characteristics of an organism.
• Dominant 


  Always expressed, even if only 1 copy is present.
• Recessive


  Only expressed if 2 alleles present.
• If a mouse has one allele for brown fur, and another allele for black fur, 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.