12-4 Mutations Mutation: A Change in DNA

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.

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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

Deletion

Inversion

Duplication

Translocation

Deletion

Inversion

Duplication

Translocation

Deletion

Inversion

Duplication

Translocation

Deletion

Inversion

Duplication

Translocation

Deletion

Inversion

Duplication

Translocation

Deletion

Inversion

Duplication

Translocation

12-4 Mutations Mutation: A Change in DNA

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