Inheritance

• A gene is a sequence of bases on a DNA molecule that codes for a protein which results in a characteristic
• • You can have one or more versions of the same gene.
  • These different versions are called alleles.
  • There can be many different alleles of a single gene but mosts plants and animals only carry two alleles of each gene, one from each parent
• The order of bases in each allele is slightly different - thats because each allele codes for different versions of the same characteristic. Alleles are represented using letters
• Humans are diploid organisms. This means we have two copies of each chromosome - one from each parent

  Its why we have two alleles of each gene.

  The allele of each gene is found at a fixed position, called a locus, on each chromosome in a pair.
• The genotype of an organism is its genetic constitution - different alleles an organism has

  This could be a list of all its alleles but usually its just the alleles for one characteristic at a time.
• The phenotype of an organism is 'the expression of the genetic constitution and its interaction with the environment'

  This just means what characteristics an organism has as a result of both its genes and the effect the environment has on its genes
• 1. At each locus in a diploid organism, the genotype can be homozygous or heterozygous. If an organism carries two copies of the same allele, it’s said to be homozygous at that locus. If an organism carries two different alleles for a gene, then it’s heterozygous.