max112
09-12-2007, 04:30 AM
mutation-- a change in the genetic material ie. DNA.
Why are mutations important?
There are several reasons:
1) they may have deleterious or (rarely) advantageous consequences to an organism
2) they are important to geneticists: the most common way we study something is to break it--ie., we search for or make a variant (mutant) lacking the ability to perform a process which we want to study. These genetic variants possess mutant alleles of the genes we are interested in studying.
3) Mutations are important as the major source of genetic variation which fuels evolutionary
change
mutations that occur in germiline cell are a heritable but mutations that take place in somatic cell (body cell) are not heritable
II. Types of Mutations
mutations may be gross (at chromosomal level) which can be detected by cytogenetical methods or be point mutation at niclotides level
A- Single nucleotide mutations:
1- silent mutation:mutation that chage the codon but it does not change the amino acid
2- missense mutation: mutation that changes the amino acid
3-nonsense mutation :mutation that chage the codon to stop codon
#transitions mutation :nucleotide substitution from purine to purine or pyrimidine to pyrimidine
#transversions mutation:nucleotide substitution from purine to pyrimidine or pyrimidine to purine
B. Frameshift mutations
These result from the insertion or deletion of one or more (not in multiples of three) nucleotides in the coding region of a gene. This causes an alteration of the reading frame: since codons are groups of three nucleotides, there are three possible reading frames for each gene although only one is used.
Chromosomal abnormalities
There are two ype of Chromosome abnormalities:
A- Numerical abnormalities: When an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy).
B- Structural abnormalities: When the chromosome's structure is altered. This can take several forms:
#Deletion: when a portion of chromsome is missing
#Duplications:A portion of the chromosome is duplicated, resulting in extra genetic material.
#Translocations:When a portion of one chromosome is transferred to another chromosome.
#Inversions:A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.
#Rings:A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material.
#Isochromosome:one of the chromosome arms is missing and replaced the other armso the two arms are the same .
I HOPE THAT I MADE A USEFUL TOPIC FOR YOU GUYS
MY NEXT TOPIC WILL BE IN THE CAUSES OF DNA MUTATIONS AND THE DNA REPAIR SYSTEM
Why are mutations important?
There are several reasons:
1) they may have deleterious or (rarely) advantageous consequences to an organism
2) they are important to geneticists: the most common way we study something is to break it--ie., we search for or make a variant (mutant) lacking the ability to perform a process which we want to study. These genetic variants possess mutant alleles of the genes we are interested in studying.
3) Mutations are important as the major source of genetic variation which fuels evolutionary
change
mutations that occur in germiline cell are a heritable but mutations that take place in somatic cell (body cell) are not heritable
II. Types of Mutations
mutations may be gross (at chromosomal level) which can be detected by cytogenetical methods or be point mutation at niclotides level
A- Single nucleotide mutations:
1- silent mutation:mutation that chage the codon but it does not change the amino acid
2- missense mutation: mutation that changes the amino acid
3-nonsense mutation :mutation that chage the codon to stop codon
#transitions mutation :nucleotide substitution from purine to purine or pyrimidine to pyrimidine
#transversions mutation:nucleotide substitution from purine to pyrimidine or pyrimidine to purine
B. Frameshift mutations
These result from the insertion or deletion of one or more (not in multiples of three) nucleotides in the coding region of a gene. This causes an alteration of the reading frame: since codons are groups of three nucleotides, there are three possible reading frames for each gene although only one is used.
Chromosomal abnormalities
There are two ype of Chromosome abnormalities:
A- Numerical abnormalities: When an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy).
B- Structural abnormalities: When the chromosome's structure is altered. This can take several forms:
#Deletion: when a portion of chromsome is missing
#Duplications:A portion of the chromosome is duplicated, resulting in extra genetic material.
#Translocations:When a portion of one chromosome is transferred to another chromosome.
#Inversions:A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.
#Rings:A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material.
#Isochromosome:one of the chromosome arms is missing and replaced the other armso the two arms are the same .
I HOPE THAT I MADE A USEFUL TOPIC FOR YOU GUYS
MY NEXT TOPIC WILL BE IN THE CAUSES OF DNA MUTATIONS AND THE DNA REPAIR SYSTEM