Chapter 4: Variation & Mutation Flashcards
when is a gene expressed
when a gene is read, transcribed and translated into a protein
what is the phenotype
by coding for proteins, genes determkine important facts of biological structure and function. these observable traits are known as the phenotype
what is variation
the diversity of genetic and phenotypic traits within and between populations
what are the mechanisms behind variation
environmental factors, mutation, and sexual reproduction
what are the types of environmental factors
external = temperature, ph, avaliability of food.
internal = action of hormones
what is epigenetics
the study of inheritable (but reversable changes in gene expression without a change in DNA sequence.
epigenetics can also influence phenotype by controlling gene expression,, and can effect growth and developement of organisms
when can spontaneous mutations occur
during cell division or DNA replication
what are mutagens
physical or chemical environmental factors that induce mutations
when do spontaneous mutations occur
during the S phase of the cell cycle, when dna is exposed during replication is vulnerable to damage.
what are the main ideas scientists have formed about mutations
mutations arise spontaneously and are not directed by the environment. mutations are persistent. majority of mutations confer disadvantages on the organisms that inherit them.
how do mutations occur during meiosis
unequal corssing over, if non-sister chromatids misalign during crossing over, one gamete may gain extra nucleotides (leading to an insertion mutation), and one may lose some nucleotides (leading to a deletion mutation).
name three physical mutagens
x-rays, UV light, nuclear radiation
what do x-rays do
gene and chromosome aberrations
what does uv light do
stuctural distortion by cross-linking neighbouring nucleotides
what does nuclear radiation
breaks in DNA strands
give an example of a chemical mutagen
mustard gas , affects the base guanine , resulting in a substitution mutation
what are point mutations
the simplest form of a mutation, just a single nucleotide within the original DNA sequence is affected by a substitution, addition or deletion.
what is substitution
occurs when one nucleotide is replaced by another, they have number of affects on the translated protein, they are the source for new SNPs
what are SNPs
single nucleotide polymorphisms, if it occurs in a gene, the mutated gene sequence can be transcribed and translated into a protein that is the same as that encoded by the original form of the gene.
what are the types of point mutations
synonymous mutation, missense mutation, nonsense mutation
what are synonymous mutations
also called silent mutations, occurs when the substituted base results in a codon that codes for the same amino acid as the original codon. this happens because there is a level of redundancy in the genetic code.
what are missense mutations
when a SNP changes the amino acid.
what are nonsense mutations
occurs when a SNP creates a new stop codon within the original gene sequence, this leads to early termination of translation of the transcribed gene sequence. results in the production of an incomplete polypeptide
what is a frameshift mutation
the reading frame for the corresponding amino acid has been nudged away from the original, can be from a gene insertion or deletion, has a profound effect on the corresponding protein
