Mutations

SB2 d Describe the relationships between changes in DNA & potential appearance of new traits including: –Alterations during replication Insertions Deletions Substitutions

What is a mutation? …any change in genetic information. Most mutations are bad, some lead to new adaptations. Really severe mutations usually result in death.

2 main types of mutations 1.Gene 2.Chromosome

Gene mutations …usually affect one or a few genes. Typically not as severe as chromosomal mutations. (Keep in mind that some genes affect a LOT of things!! Example: genes that code to make hormones.)

Types of gene mutations 1)Substitution mutation – a different base is used (ex. A is put in instead of C) Also called a Point Mutation because 1 nucleotide base is incorrect. ATC GAG CTA  ATC GAG ATA

2. Deletion mutation – 1 nucleotide is removed. **causes a “frame-shift” mutation!! (Ex: GAT CGA CCA…  GAC GAC CA..) This causes every nucleotide to shift to the left and none of the sequence of DNA after the deletion will be correct!

3. Addition mutation – 1 nucleotide base is added. ** causes a “frame-shift” mutation! (Ex: TGA CAT GGA...  TGG ACA TGG A..) The sequence shifts to the right, all the following bases will be out of order.

Things to keep in mind! Some mutations are genetic…you got them from your parents! Some mutations are random. Some mutations are caused by exposure to mutagens, things that cause mutations. (Ex. UV radiation, chemicals, x-ray radiation etc…)

Chromosomal mutations Affect many genes. Are usually very severe. Occur during mitosis or meiosis.

Types of chromosomal mutations 1)Deletion – loss of all or part of a chromosome 2)Duplication – an extra portion of a chromosome was duplicated 3)Inversion – piece of chromosome breaks off and reattaches backwards 4)Translocation – piece of chromosome breaks off and reattaches to a different chromosome

If a chromosomal mutation results in a change in the number of chromosomes it is called NONDISJUNCTION. Nondisjunction usually happens during meiosis and the chromosomes do not separate properly.

Gene linkage Some genes on the same chromosome are virtually “linked”, they are inherited together. Crossing over may separate some of these genes. Some genes are “sex-linked”, they are on the sex chromosmes.

Chromosome mapping Determines how close genes are on a chromosome & how likely the genes are to be “linked” We use “MAP UNITS” to signify distance.

Chromosome Map

The closer 2 genes are to each other (fewer map units) the more likely they are to be inherited together. EX: a gene is 4 map units away from a different gene, there is only a 4% chance that the traits will be separated by crossing over.