Variation

• The human genome project:

  In 2003, the first complete human genome was decoded. It produced a map of 3.3 billion base pairs in one set of 46 chromosomes. Since then, other human genomes have been mapped out and shown that over 99% of DNA bases in different people are the same.
• The human genome project:

  It was important because:

  • it can indicate a persons risk of developing a genetic disease
  • it can help identify which medicines might be best to treat a persons illness and its potential applications within medicine.
• Genetic variation- different characteristics a result of mutation and sexual reproduction. Examples- blood group
• Environmental variation- different characteristics caused by an organisms environment. E.g the language you speak or length of hair.
• Variation is in two groups:

  1. Discontinuous variation- where the data can only take a limited set of values. It should be shown as a frequency diagram with spaces between the bars.
• 2. continuous variation- where the data can be any value in a range. It should be shown as a frequency diagram with no spaces between the bars.
• Continuous data for variation often forms a bell-shaped curve, known as a normal distribution.

  It is called this because it is what is expected for a large amount if data for a characteristic where -

  • the most common value is the middle value in the whole range
  • the further a value is from the median, the fewer individuals have that value.
• Most phenotypic features are the result of multiple genes rather than single gene inheritance.
• A change in a gene that creates a new allele is called a mutation. Mutations often occur during cell division when there is a mistake copying DNA.
• Most mutations have no effect on the phenotype.
• Genetic diagrams show the possible combinations of alleles when two organisms breed. They can be used to predict the ratio of the phenotypes. A dominant allele is shown by a capital letter. The recessive allele has the lower case version of the same letter. A dominant allele is written before the recesive one.
• Two of your chromosomes determine what sex you are, they are your sex chromosomes.

  Male = X and Y chromosomes

  Female = X and X chromosomes
• A family pedigree chart shows how genotypes and their resulting phenotypes are inherited in families.