Ch 3 Lecture (The Interrupted Gene) Flashcards
Interrupted Genes
Genes for which the coding sequence is not continuous due to the presence of introns
Primary Transcript (pre-mRNA)
The original unmodified RNA product corresponding to a transcription unit
RNA Splicing
The process of excising introns from RNA and connecting the exons into a continuous mRNA
Mature Transcript
A modified RNA transcript that moves to cytoplasm for translation
Modifications: alterations to 5’ and 3’ ends & removal of introns
Mutations in Exons
Can affect polypeptide sequence
Mutations in Introns
Can affect RNA processing
Usually deleterious
Most are point mutations at the intron-exon boundary
–most common outcome is a nonsense mutation (X –> stop)
Homologous Genes
Genes share a common ancestor
Negative Selection
Selection against mutations that alter the function of the polypeptide
Not having changes in exons is favored
Positive Selection
An advantageous mutation has a greater fitness relative to those without the mutation
Having changes in exons will be favored
Overlapping Gene
A gene in which part of the sequence is found within part of the sequence of another gene
Nested Gene
Complete gene inside of the intron of a larger gene
Alternative Splicing
Production of different polypeptides by including or excluding individual exons or choosing between alternative exons
Gene Family
A set of genes within a genome that encode related or identical RNA or proteins
Derived by duplication of an ancestral gene and accumulation of changes in sequence between copies
*More similar
Superfamily
A set of genes all related by presumed descent from a common ancestor
Now show considerable variation
*Very different but still related
Orthologous Genes
A special type of homolog
Related genes in different species
what stays the same in homologous genes
exon length and organization
why do introns mutate more rapidly than exons
exons are under selective pressure to produce a specific polypeptide with a specific function
introns may be … than exons if the gene is under positive selection
more highly conserved
when introns are being conserved, what parts are the most important
branch points and splice sites
example of positive selection
snake venom and prey resistance
why are there more interrupted genes in higher-level eukaryotes
Specialized cells, specialized functions, larger, make multiple proteins.
the overal length of a eukaryotic gene is determined largely by
the length of the introns
