Lecture 21 - Dynamic Genomes and Creation of Diversity

Question 1

Genetic variation in bacteria is due to…..

Answer 1

Mutations! Most frequently arise due to mistakes made during DNA replication and repair.

Question 2

Conjugation

Answer 2

Bacterial mating - pass F plasmid from F+ male to F- female through sex pilus.

Conjugation = conjugal visit, f plasmid = fuckin

Question 3

F plasmid

Answer 3

Passed between bacteria, infrequently integrates into host chromosome

Can carry genes for antibiotic resistance

Question 4

Transformation

Answer 4

Bacteria are lysed and DNA fragmented - taken up by other bacteria and can be inserted into genome

Question 5

Bacterial homologous recombination

Answer 5

2 homologous, ds DNA sequences are lined up, nick is made allowing one strand to invade and anneal to complementary strand. The displaced strand is nicked and anneals to the other homologue at which point the ends are ligated to complete formation of the cross-strand exchange

Plasmids integrate into chromosome via short regions of homology

Question 6

Transduction

Answer 6

Infection by bacteriophage whose genome can be integrated into the host bacterial’s.

When the viral DNA is excised, it can take some bacterial DNA with it. These are then packaged into new bacteriophages which go on to infect more bacteria.

Question 7

Transposon

Answer 7

Relatively short DNA sequence that has the capacity to move from place to place within the genome of organisms by a process called transposition

Contribute to genetic diversity by:

1. Disrupting genes where they land
2. Altering expression of neighbor genes
3. Facilitating rearrangement of bac chromosome through homologous recombination
4. Hopping into plasmids or bacteriophages
5. Amplifying copies of antibiotic resistance

Question 8

Independent assortment

Answer 8

At meiosis, maternal and paternal chromosome pairs segregate independently from each other during meiosis.

Question 9

Eukaryotic homologous recombination

Answer 9

Induced during meiosis after DNA replication. Homologues pair with help of cohesins

Avg of 3 crossovers per chromosome per meiosis

Question 10

Retrotransposons in Humans

Answer 10

Small mobile DNA elements in humans - (ex LINE 1, SINEs, Alu elements)

Contribute to human genetic diversity

1. Disrupt gene fxn by inserting w/in exon of gene (ex. insertion in Factor VIII gene for hemophilia)
2. Affect expression of genes
3. Create sites for illegitimate homologous recombination (unequal crossovers)

Question 11

Describe the creation of gene families by unequal crossovers

Answer 11

Transposon insertions that flank a gene can lead to mis-alignment and ultimately lead to “unequal crossing”

Can lead to exon amplification or duplication

Extreme example - dystrophin, probably arose from exon amplification

Question 12

Exon shuffling

Answer 12

The movement of whole genes by the transposition of flanking transposable elements

Question 13

Describe the role of retroviruses and genetic instability

Answer 13

Virus integrates genome into host DNA, can have the following impact on host DNA

1. Disrupts gene function by inserting into exon
2. Since viral promoters can be very active, insertion can inappropriately turn on neighboring genes
3. Upon packaging of new virus, neighboring genes can be incorporated into viral genome and passed on

Question 14

The average person inherits _____ loss of function alleles. And on average, every person is heterozygous for ________ varients known to caused inherited disorders.

Answer 14

250-300

50-100