IV.Source of Gene Variations: When cells divide each DNA molecule in the cell makes exactexact copies of itself. But sometimes the cell makes a mistakemistake; bases may pair up incorrectlyincorrectly. The codoncodon are changed the alteredaltered gene is passed on to the new cell.

A- MutationMutation is any permanentpermanent change in the DNADNA of a cell.

1.Mutation increasesincreases with the exposure of DNADNA to some chemicalschemicals ands radiation that damagedamage the DNA molecule.

B.Chromosome Mutation: When a piecepiece of chromosome breaksbreaks and are rearrangedrearranged or lostlost. During meiosis chromosomes mutationmutation may occur when chromosomes do not separate evenlyevenly.

1.Muscular DystrophyDystrophy= Weak muscles.

2.Down Syndrome or TrisomyTrisomy 21= is caused as a result of a sex cell having too many 21st21st chromosomeschromosomes. The fertilized egg, contains threethree 21st chromosomeschromosomes instead of two.

3.Importance of Mutations= are a source of newnew traits or new formsforms of traits.