Download - 12-4 Mutations Mutation: A Change in DNA Mutation – any change in the DNA sequence that can also change the protein it codes for Mutations in Reproductive.

12-4 Mutations

Mutation: A Change in DNA

• Mutation – any change in the DNA sequence that can also change the protein it codes for

• Mutations in Reproductive Cells

• If mutation occurs in egg or sperm the altered gene would become part of the genetic makeup of the offspring

• Sometimes the mutation is so severe that the embryo does not survive

• In rare cases a gene mutation may have positive effects

• Mutations in Body Cells

• If the cells DNA is changed this mutation would not be passed on to offspring

• But the mutations can cause harm to the individual

2 Types of Mutations in DNA

1. Point Mutation

• Is a change in a single base pair in DNA

• A change in a single letter changes the meaning of this sentence

2. Frameshift Mutation

• A mutation in which a single base is added or deleted from DNA

• This mutation would cause nearly every amino acid in the protein after the deletion to be changed.

mutatedbase

Chromosomal Mutations

• Chromosomal Mutations – changes in chromosomes during replication. Parts can be broken or lost.

• They occur in all living organisms, but they are especially common in plants

• Although rare, changes in an organisms chromosome structure do occur.

• Chromosomal mutations are rarely passed on to the next generation because:

• The zygote usually dies

• The mature organism is usually sterile

• 4 Types of Chromosomal Mutations

1. Deletion – a fragment of a chromosome breaks off, it can be lost when a cell divides

2. Duplication – the chromosome fragment attaches to its homologous chromosome, which will then carry two copies of a certain set of genes

3. Inversion – fragment reattaches to the original chromosome in the reverse orientation

4. Translocation – a fragment may join a nonhomologous chromosome

Causes of Mutations

• Spontaneous Mutations – a mistake in base pairing during DNA replication. It occurs at random or at any given moment

• Mutagen – any agent that can cause a change in DNA

• Ex. Chemicals, radiation, high temperatures

Repairing DNA

• When mistakes do occur repair mechanisms fix mutations

• Proofreading Enzymes – reads the DNA strand and checks it for mistakes

• Repair Enzymes – fixes any mistakes in the DNA strand

Mistakes in Meiosis

• Sometimes accidents occur during meiosis and chromosomes fail to separate correctly

• Nondisjunction – failure of homologous chromosomes to separate

• During meiosis I one chromosome from each pair is supposed to move to opposite poles but occasionally both chromosomes of a pair move to the same pole

• Trisomy – 1 extra chromosome (47)

• Ex: extra chromosome on pair number 21 – down syndrome

• Monosomy – missing 1 chromosome (45)

• Ex: missing chromosome on pair number 23 – turner syndrome

• Tetraploid – 2 extra chromosomes (48)

• Polyploids – organisms with more than the usual number of chromosome sets

• Is rare in animals and almost always results in death.

What is abnormal about this person’s chromosomes?

Deletion

Inversion

Duplication

Translocation