11: mutations, viruses, evolution Flashcards
Homologous structures
Structures with the same form but different functions (ie, forearms in mammals) -> divergent evolution (same common ancestor)
Analogous structures
Structures with different shapes but the same function (ie, bird vs. butterfly wings) -> convergent evolution (evolved independently)
Allopatric speciation
Populations are geographically separate and accumulate differences due to physical separation
Sympatric speciation
Populations are not geographically isolated but by other means
Prezygotic isolation mechanisms
- Ecological isolation - diff. habitats
- Temporal isolation - diff. reproductive schedules
- Behavioral isolation - diff. mating rituals
- Mechanical isolation - diff. reproductive structures
Postzygotic isolation mechanisms
- Hybrids don’t survive
- Hybrids are infertile
Conserved traits (+ significance)
Traits that are almost identical across different species; indicates that the trait is very advantageous regardless of species and mutations in that trait are likely fatal
Double-stranded breaks fixes
- Sometimes only 1 chromosome (of the homologous pair) is damaged , so the cell can use the homologous chromosome as a template for a new strand of DNA
- Non-homologous end joining - broken section of DNA is excised and the remaining stitched together by ligase (leads to missing sections of DNA)
- Apoptosis
Slipped mispairing
Since there are codon repeats in many genes, one strand of the double helix may match with a codon farther downstream than the correct one, leading a loop to form
Excision -> at least 1 codon is lost
Leave loop -> DNA is difficult to package into histones
Apoptosis -> cells may decide that the mutation is too harmful
Triplet expansion
Codons are replicated too many times and accumulate over time as the same repeated code gets copied again and again
Inversion of chromsomes
- A segment of a chromosome (with multiple alleles) is “upside down,” meaning alleles are in a different order
- During synapsis and crossing over (during Prophase I) chromosomes cross over at the same locations (loci), not necessarily ensuring they have the same alleles
-> Exchange of different length alleles
-> No longer homologous chromosomes
Transposition
- Transposon enzyme moves gene segments from 1 region of a chromosome to another region on the same chromosome / a different chromosome
- Increases genetic diversity because it can turn off certain genes (diverse gene expression)
- Does so because when a cell sees a long stretch of unfamiliar, transposed DNA, it may inactivate the entire gene, making it not code for a protein
Insertional inactivation
- Sometimes due to transposition
- Can be positive or negative
Enveloped vs. non-enveloped viruses
Animal viruses are typically enveloped
Bacteriophages typically aren’t
Ways for viruses to enter cells
- Envelope fuses with membrane and viral genome enters (only if virus has envelope - so animal viruses)
- Endocytosis (virus tricks cell into letting it enter by. using glycoproteins)
Lytic cycle
1) Bacteriophage injects genetic material into cell
2) Phage genome and proteins assemble into more viruses
3) Cell lyses, killing the host cell; viruses infect others
Lysogenic cycle
1) Bacteriophage injects genetic material into cell
2) Viral genetic material is incorporated into host cell DNA; is silent initially but can be triggered
3) Cells reproduce, copying viral genome as well
4) When the viral genome (prophage) detaches from the chromosome, it turns on, and the cell enters the lytic cycle
Host cell components for reproduction
Nucleic acids, enzymes, ribosomes, tRNAs, amino acids, ATP, and other things needed to synthesize viral proteins
Internal viral components for reproduction
- viral RNA polymerase (host cells don’t have it)
- glycoproteins
DNA genome infection steps
1) Virus enters cell and releases viral DNA
2) Host enzymes replicate the viral DNA
3) Host enzymes transcribe the viral DNA into viral mRNA
4) Ribosomes use viral mRNA to make viral proteins
5) Viral DNA and viral proteins assemble into new viruses, which leave the cell
RNA virus infection
1) Virus enters cell and releases viral RNA
2) Viral RNA Polymerase makes the complementary strand to the original viral RNA (single strand)
3) More copies of double-stranded viral RNA are made
4) Viral RNA functions as mRNA
5) Ribosomes produce viral proteins
6) Virus self-assembles and buds from cell
Retrovirus infection
1) Virus enters cell and releases viral proteins, viral RNA, and reverse transcriptase
2) Reverse transcriptase catalyzes 1 strand of RNA to 1 strand of DNA
3) Reverse transcriptase synthesizes the complementary DNA strand to the first
4) Double-stranded DNA is incorporated into host genome as a provirus
5) Ribosomes transcribe the provirus (DNA) into mRNA
6) The mRNA codes for viral proteins
7) New viruses assembled and leave
Evidence for evolution
- Similar nucleotide sequences
- Fossil records indicate homologous structures
- Conserved traits
- Embryonic development
- Vestigial structures
