Chapter 7.7 Flashcards
MUTATION
Is a change in a cell’s DNA’ sequence ( either in a protein coding gene or in non- coding DNA such as an enhancer.)
Th significance of mutations
- they change the structure of its encoded protein so that it can no longer do its job.
- They provide genetic variability. they are the raw materials for evolution because they create new alleles
ALLELES
Mutatation create new alleles. They are a variation of a gene.
Exceptfor identical twins we all have different combinations of for all our genes
POINT MUTATION
Substitution of one DNA base for another
SUBSTITUTION MUTATION
It is the replacement of one DNA base with another.
It is a silent mutation
SILENT MUTATIONS
When a mutation occurs but the mutated gene still encodes the same protein as the original gene version.
They occur because more than one codon encodes most amino acids
MISSENSE mutation
occurs when a substition mutation changes a base triplet so that it specifies a different amino acid.
This may drastically change the protein’s shape and thus its function
NONSENSE MUTATIONS
A base triplet specifying an amin acid changes into one that encodes a stop codon (cystic fibrosis)
3 types of POINT MUTATIONS
- SUBSTITUTION MUTATIONS
- BASE INSERTIONS AND
- DELETIONS
2 Types of SUBSTITUTION MUTATIONS
- MISSENSE- specifies for a different amino acid changing the shape of the the protein
- Nonsense cause the base to to code for a “ stop”codon shortening the polypeptide
eg. BASE INSERTIONS AND DELETIONS
FRAMESHIFT MUTATION
FRAMESHIFT MUTATION
adds or deletes nucleotides in any number other than a multiple of three changing the reading frame and altering the amino acid sequence.
EXPANDING REPEAT MUTATION
the number of copies of 3 or 4 nucleotides sequence increases over several generations.
With each generation the symptoms begin earlier or more sever ,or both.
REPLICATION ERRORS/ SPONTANEOUS SUSTITUTION MUTATON
usually originates a DNA replication error.
Replications errors can also cause insertions and deletions, especially ingenues with repeated base sequences.
MUTAGEN
Is any external agent that induces mutations
Egs
UV radiation, X-rays, nuclear accidents, chemicals
List the causes of mutations
- Spontaneous substitution mutation/addition and deletion= Replication Errors
- Mutagens
- Errors in Meiosis ( misalignment at at crossover point)
- Inverted chromosomes
- two different chromosomes fusing together
- TRANSPOSABLE ELEMENT
2.
TRANSPOSABLE ELEMENT MUTaTIONS
or TRANSPOSON is a Dna sequence that can jump within the genome.
It can insert itself randomly into chromosomes disrupting a gene’s function or leaving a gap in a gene when it leaves.
GERMLINE MUTATION
occurs in the cells that give rise to sperm and eggs
Why are germline mutations heritable
They are heritable because mutated Dna will be passed down to at least some of the sex cells that the organism produces
the result of inheriting a germ line mutation
every cell in that organism produces
Non heritable mutations
SOMATIC MUTATIONS
SOMATIC MUTATIONS
occurs in non sex cells.
They are non- heritable
The mutation is not passed down to their offsprings
Why are mutations important
- They produce genetic variability
- They are raw materials for evolution because they create new alleles
- Homeotic genes
- Improves reproductive success in some species ( bacteria)
- Allow some viruses to jump from animal to humans
- Induced mutations create crop variety
ALLELES
Variants of a gene
Except for identical twins everyone has a different combination of genes
Allele combinations and fitness
In every species individuals with some allele combination reproduce more successfully than others
NATURAL SELECTION EDITS OUT THE LESS FAVORABLE ALLELE COMBINATIONS
HOMEOTIC GENES
They cause the development of specific structures in plants and animals. They control the pattern of body formation during early embryonic development
They encode transcription factors that are expressed during the development of an embryo. If the transcription factors are faulty, the signals that control the formation of an organism’s body part become disrupted
how have HOMEOTIC genes affected animal evolution
limb modifications trace their origins to homeotic mutations
e.g. of how mutations enhance an organisms reproductive success
Antibotic Resistant Bacteria ( offsprings are are unaffected by antibiotic drugs)
- ramdom mutations in viral genomes enable viruses to jump from other animals to humans
- Scientist induce mutations to learn how normal genes function
- they are also induced to create variety
What is a mutation?
A mutation is a change in the DNA sequence of a cell.
What are the types of mutations, and how does each alter the encoded protein?
A point mutation changes one or a few base pairs of genes. Point mutations include substitution mutations (which replace one DNA base for another), insertions, and deletions. Substitution mutations might change one amino acid to another in the encoded protein (which is called a missense mutation), might change an amino acid to a stop codon (which is called a nonsense mutation), or might not change an amino acid (which is called a silent mutation). Insertions of deletions of more or fewer than three nucleotides will shift the “reading frame” of the gene; these frameshift mutations might alter many amino acids in the protein, drastically changing its shape and function. An insertion of three nucleotides adds one amino acid to the encoded protein. A deletion of three nucleotides removes one amino acid from the encoded protein. Expanding repeat mutations increase the number of copies of three-or four-nucleotide sequences over several generations. This causes extra amino acids to be inserted into a protein, deforming it.
What causes mutations
Mutations are caused by DNA replication errors, errors in crossing over during meiosis, chromosome inversions and translocations, or exposure to chemicals or radiation.
. What is the difference between a germline mutation and a somatic mutation?
A germline mutation is one that occurs in a cell that will give rise to a sperm or an egg cell. A somatic mutation occurs within a non-germline body cell.
How are mutations important?
Mutations are used to learn how genes normally function and to develop new varieties of crop plants. Mutations can also be used to trace the evolution of viruses and other infectious agents.
Why can silent mutations occur
Because more than one codon encodes most amino acids
