Mutations

Duplication

- a change to a chromosome in which a portion of the chromosome is duplicated, resulting in extra genetic material. - known human disorders include Charcot-Marie-Tooth disease type 1A which may be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17.

Deletion

- a change to a chromosome in which a portion of the chromosome is missing or deleted. - known disorders in humans include Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; Cri du chat syndrome is due to a partial deletion of the short arm of chromosome number 5.

frameshift mutation: deletion

- a nucleotide is lost or deleted from a DNA sequence example if this T gets deleted that our ex) If everything shifts one space to the left, all of these spaces will also have shifted one space to the left so, as well as this codon being different, all of these subsequent ones will be as well

Chromosome mutation

- alterations of chromosome number or structure cause some genetic disorders - large-scale chromosomal alterations often lead to miscarriages or cause a variety of developmental disorders or even cancers - breakage of a chromosome can lead to four types of changes in chromosome structure: deletion, duplication, inversion, and translocation

Mutation

- any change in the nucleotide sequence of DNA - can involve large regions of a chromosome or just a single nucleotide pair - can cause the overall sequence of amino acids to change so the protein that it ends up forming would be different as well, meaning that it can have a different shape or function

types of mutations within a gene:

- base substitutions - base insertions or deletions

Base substitutions may cause...

- changes in a protein that prevent it from functioning normally - occasionally, a base leads to an improved protein that enhances the success of the mutant organism and its descendants - much more often, though, mutations are harmful (if a base substitution changes an amino acid codon to a stop codon, a shortened, probably nonfunctional, polypeptide will result) (prematurely terminated polypeptide)

DNA makes up...

- genes and genes can code for proteins that influence different traits. - so when a mutation in DNA happens, different proteins can be produced which can affect an organism's traits.

Inversions are...

- less likely than deletions or duplications to produce harmful effects, because in inversions all genes are still present in their normal number - many deletions in human chromosomes, however, cause serious physical and mental problems

frameshift mutation

- mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide - changes the amino acid sequence from this point forward

Mutations involving the insertion of deletion of one or more nucleotides in a gene...

- often have disastrous effects and are more dangerous - bc mRNA is read as a series of nucleotide triplets (codons) during translation, adding or subtracting nucleotides may alter the reading frame (triplet grouping) of the message - all the nucleotides that are "downstream" of the insertion or deletion will be regrouped into diff codons, resulting in a nonfunctional polypeptide - lead to many amino acid changes

Mutations are...

- random But there can be factors that can make mutations more likely to occur: - External factors, like certain types of chemicals or excessive radiation - Internal factors, like an event that causes a problem with DNA replication in interphase.

how can mutations be useful?

- rich diversity of genes in the living world, a diversity that makes evolution by natural selection possible - essential tools for geneticists (creates different alleles needed for genetic research)

Translocation

- when a portion of one chromosome is transferred to another chromosome. - sometimes, parts of different chromosomes switch places (reciprocal exchange). - may or may not be harmful ex) some ppl w Down syndrome have only part of a third chromosome 21; as a result of a translocation, this partial chromosome is attached to another non homologous chromosome

frameshift mutation: insertion

- when an extra base is inserted/added into the sequence - these mutations are actually a lot worse than substitution mutations are because it means that all the subsequent bases are shifted along by one which alters all of the subsequent columns and so the amino acid chain after that point would be completely different

Which type of mutation is responsible for new variations of a trait?

all types besides silent mutations

Gene mutation

mutations that affect a single gene by changing its base sequence, resulting in an incorrect, or nonfunctional, protein being made

Which type of mutation stops the translation of an mRNA molecule?

nonsense mutation

Which type of mutation does not result in an abnormal amino acid sequence?

silent mutation

substitution: missense mutation

when a substitution changes the amino acid

substitution: nonsense mutation

when a substitution changes the amino acid to a "stop"

substitution: silent mutation

when a substitution does not change the amino acid ex) if a mutation causes an mRNA codon to change from GAA to GAG, for instance, no change in the protein product would result because GAA and GAG both code for the same amino acid (glu)

What kind of gene mutation is more likely to result in a nonfunctional protein, a frameshift or a substitution point mutation? Why?

Frameshift - most/all of the amino acids after the insertion/deletion will change leaving a non-functional protein. - substitution will only affect one amino acid (may be silent which would leave the protein unchanged). - if it is a missense it may cause a problem or it may cause a new variation. - if the amino acids are similar in chemical properties it may not change the protein much at all - a nonsense mutation would most likely cause a non-functional protein but frameshifts guarantee a non-functional protein due to all of the subsequent changes.

Inversion

a change to a chromosome in which a portion of the chromosome has broken off, turned upside down, and reattached, therefore the genetic material is backward.

substitution

a mutation in which a nucleotide or a codon in DNA is replaced with a different nucleotide

Why are chromosome mutations potentially more serious than gene mutations?

They involve hundreds/thousands of nucleotides which would likely encompass more than one gene. More genes being affected would cause more issues.