12.4 Mutations

 What is a mutation and where can it occur? Inheritable change in genetic code 99.9 % are harmful, only 0.1% are helpful  Any change in an organisms DNA  Some mutations affect a single gene, while others affect an entire chromosome.  Chromosomal mutation = Changes in number or structure of chromosome

 Mutations that affect a single gene may happen:  During replication or cell division  Spontaneously  Because of mutagens in the environment you’re exposed to  Chromosomal mutations occur during Meiosis

 Replication errors  If DNA polymerase does not fix errors, they build up over time and affect how the cell works.  Studies suggest that mutations are a significant cause of aging

 Mutagens  Agents in the environment that can change DNA, speed up the rate of replication errors, in some cases even breaking DNA strands  UV rays in sunshine and industrial chemicals  Some kids exposed to radiation from the Chernobyl disaster were affected in such a way that they secrete a compound which means they can stick metal to them, so they are effectively magnetic  Mutations in the gene that controls the development of the rod in your eye gives some people night vision.

 Gene Mutations ( 2 types)  Chromosomal Mutations ( 4 types) mutate d base

 Point mutation  involves a change in only 1 base  Frameshift mutation  one or more bases are inserted or deleted

Mutations happen both in somatic cells and gametes. Mutations in body cells do not affect offspring. Why? Mutations in gametes (sex cells) can be harmful or beneficial to offspring. –These mutations are the underlying source of genetic variation. –Often the effects of mutations in gametes is so harmful that the offspring does not develop properly or dies before they can reproduce Natural selection often removes mutant characteristics from a population when they are less adaptive More rarely, a mutation results in a more beneficial characteristics, these mutations are favored by natural selection and therefore get passed on. Somatic cells vs Gametes

 Enzymes (DNA polymerase) proofread the DNA and replace incorrect nucleotides with correct nucleotides  These repair mechanisms work extremely well, but they are not perfect  The greater the exposure to a mutagen such as UV light, the more likely is the chance that a mistake will not be corrected

Chromosomal mutations —involve changes in the number or structure of chromosomes  Deletion  Loss of all/part of chromosome  Duplication  Segment of chromosome is repeated  Inversion  Part of chromosome is reversed of its usual direction  Translocation  Part of one chromosome breaks off and attaches to another non- homologous chromosome