11: mutations, viruses, evolution

Question 1

Homologous structures

Answer 1

Structures with the same form but different functions (ie, forearms in mammals) -> divergent evolution (same common ancestor)

Question 2

Analogous structures

Answer 2

Structures with different shapes but the same function (ie, bird vs. butterfly wings) -> convergent evolution (evolved independently)

Question 3

Allopatric speciation

Answer 3

Populations are geographically separate and accumulate differences due to physical separation

Question 4

Sympatric speciation

Answer 4

Populations are not geographically isolated but by other means

Question 5

Prezygotic isolation mechanisms

Answer 5

• Ecological isolation - diff. habitats
• Temporal isolation - diff. reproductive schedules
• Behavioral isolation - diff. mating rituals
• Mechanical isolation - diff. reproductive structures

Question 6

Postzygotic isolation mechanisms

Answer 6

• Hybrids don’t survive
• Hybrids are infertile

Question 7

Conserved traits (+ significance)

Answer 7

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

Question 8

Double-stranded breaks fixes

Answer 8

• 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

Question 9

Slipped mispairing

Answer 9

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

Question 10

Triplet expansion

Answer 10

Codons are replicated too many times and accumulate over time as the same repeated code gets copied again and again

Question 11

Inversion of chromsomes

Answer 11

• 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

Question 12

Transposition

Answer 12

• 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

Question 13

Insertional inactivation

Answer 13

• Sometimes due to transposition
• Can be positive or negative

Question 14

Enveloped vs. non-enveloped viruses

Answer 14

Animal viruses are typically enveloped
Bacteriophages typically aren’t

Question 15

Ways for viruses to enter cells

Answer 15

• 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)

Question 16

Lytic cycle

Answer 16

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

Question 17

Lysogenic cycle

Answer 17

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

Question 18

Host cell components for reproduction

Answer 18

Nucleic acids, enzymes, ribosomes, tRNAs, amino acids, ATP, and other things needed to synthesize viral proteins

Question 19

Internal viral components for reproduction

Answer 19

• viral RNA polymerase (host cells don’t have it)
• glycoproteins

Question 20

DNA genome infection steps

Answer 20

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

Question 21

RNA virus infection

Answer 21

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

Question 22

Retrovirus infection

Answer 22

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

Question 23

Evidence for evolution

Answer 23

• Similar nucleotide sequences
• Fossil records indicate homologous structures
• Conserved traits
• Embryonic development
• Vestigial structures