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BIOL 1101 > Lecture 8: Genetic Recombination > Flashcards

Lecture 8: Genetic Recombination Flashcards

1
Q

What is the outcome of mitosis

A

genetically identical cells

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2
Q

Lottery and Genetic Recombination Analogy

A
  • you wouldn’t put the same number on the tickets you would put different ones for greater success
  • cells will genetically recombine to help with success, so that hopefully as environment changes we can increase the amount of winning combos to keep organisms alive
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3
Q

Why are we so diverse (3 reasons)

A

1) mutation
- alter genes and their outcomes
2) random fertilization
- any sperm+any egg
3) recombination
- reshuffle genes to provide evolutionary advantage to continue species

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4
Q

Mechanism of Genetic Recombination

A

a) requires 2 DNA molecules that similar but non-identical

b) Homology allows DNA on different molecules to line up and recombine precisely

c) Enzymatic cutting + pasting of both DNA backbones from each of 2 DNA molecules required for recombination

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5
Q

what kinds of DNA are similar but not identical

A

homologs chromosomes
- we need this DNA bc 2n (mom and dad are similar to each other, dipoles are homologs)
- same genes, same order

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6
Q

Simplified model of genetic recombination

A

We enzymatically cut and paste backbone of DNA and eventually re-seperate them
- they are then recombined

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7
Q

Genetic Recombination in Bacteria

A

occurs in E.Coli

  • BACTERIAL CONJUGATION: brings DNA of two cells into close proximity
  • TRANSFORMATION and TRANSDUCTION provide additional sources of DNA for recombination
  • Some bacteria genetically reshuffle as genes are transferred and recombined with existing DNA (genetically identical clones allow for this, we basically worked with them and manipulated them for understanding)
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8
Q

Genetic Recombination in E.Coli

A

Prototrophs- bacteria grow on minimal media because they make their own a.a (all 20)

Auxotrophs- bacteria with mutations does not grow on minimal medium

  • Three letter gene name: + normal, - mutated allele
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9
Q

Complete vs Minimal Medium

A

Prototrophs ON MINIMAL
- have full complement of nutrients don’t need the complete media

Auxotrophs ON COMPLETE
- missing some nutrients so they need the complete media

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10
Q

Replica Plating

A

technique to
1) identify prototrophs versus auxotrophs
2) identify+count genetic recombination in bacterial colonies

PROCESS:
In replica plating, a master plate containing a complete medium allows the growth of both prototrophic (photo) and auxotrophic (auxo) mutants because it provides all necessary nutrients, while a minimal medium only supports prototrophic mutants that can synthesize all required nutrients, thus not allowing auxotrophic mutants to grow.

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11
Q

Experimental Evidence for Genetic Recombination in Bacteria

A

Lederberg and Tatum

demonstrated genetic recombination in bacteria by mixing two strains of E. coli (auxo), leading to the formation of prototrophic colonies that could grow without specific nutrients, indicating that genetic material was exchanged.

important bc it shows that bacteria can exchange genetic information important for antibiotic resistance

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12
Q

Bacterial Conjugation

A

Bacterial recombination by conjugation:
- bacteria are haploid
- sex pilus connects 2 bacteria
- donor sends DNA via cytoplasmic bridge to recipient

Recipient Undergoes Recombination
Plasmids: Circular, non chromosomal transferable DNA (independent of bacterial chromosomes)
R Plasmids: confer resistance to antibiotics (have specific genes that are resistant to antibiotics)

= HORIZONTAL GENE TRANSFER

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13
Q

VERTICAL TRANSFER

A

new transferred genes from 1 bacterial cell to another
- from parent to offspring

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14
Q

Bacteria will get homologs chrosomes from

A

another bacterial cell, donor will send pilus to connect the bacteria

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15
Q

What does the F factor have genes for

A

genes to encode for sex pilus
- cytoplasmically connects F+ cell to F- cell
- F- cell converts to F+ cell
- No recombination

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15
Q

F Factor + Conjugation

A

we need this to make sex pilus
- Donor cell must have F factor (fertility plasmid)

F+ cells = donors with F factor
F- cells = recipients w/o F factor

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16
Q

Difference between F+ and F-

A

F+ = transfers a copy of F- plasmid to recipient to F- to F+ so that is becomes a donor

  • Just copying/sending chromosome, no actual genetic recombination occurs *
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17
Q

Transfer of Genetic Mutation During Conjugation

A

F Factor plasmid backbone cut
- 1 of 2 strands is sent over to recipient and simultaneously is being replicated
- allowing for double strands of DNA in both cells = ROLLING CIRCLE REPLICATION

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18
Q

Is F Plasmid transferred in Rolling Circle Replication

A

Yes
- no bacterial chromosome has been moved over yet, so recombination cant occur yet

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18
Q

Hfr Cells and Recombination

A

Hfr integrate F factor into bacterial chromosome through recombination:
- Her cells can conjugate with F- cells
- Recipient becomes partial diploid

Hfr Cells- high frequency cells ex F+ plasmid

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19
Q

How does genetic recombination occur

A

double-crossing over in recipient
- new generations have recombined DNA

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20
Q

F factor into chromosomal DNA yield

A

Hfr cell

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21
Q

gene mapping

A

genes that are closest
- increases likelihood of getting across

  • mutated versions of genes are therefore, homologs
    = similar but not identical

**The frequency of recombination with all genes on chromosomes. If a particular gene has an increased frequency, its clear to frequency plasmid
- increased likelihood of making it across sex pilus

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22
Q

Partial Diploid

A

bacteria that possesses 2 copies of some genes, typically due to the presence of an extra piece of DNA, such as a plasmid, along with its chromosomal DNA.

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23
Why isn't the full chromosome not always sent
- because the sex pilus is deconstructed = remains a F- cell, because when you cut F plasmid not all of it is transferred PARTIAL DNA IS TRANSFERRED AND DNA RECOMBINATION OCCURS
24
Mapping genes by conjugation
- mated Hfr and F- cells that differ in number of alleles - at regular intervals after conjugation commenced, remove cells and break apart mating pairs - cultured separated cells and analyzed for recombinants *greater time to conjugate before separation, the greater number of donor genes into recipient*
25
The order and time at which genes were transferred
able to map and assign relative positions of several genes of E. coli chromosome
26
Transformation
occurs when bacteria take up DNA from disintegrated bacteria - linear fragments recombine by double crossing - transformation bacteria usually have DNA protein in wall
27
Artificial transformation (part of transformation)
- alters cell membrane for DNA penetration electroporation: *recipient can grab DNA from dead cell/environment* - can be or a natural availability for some bacteria, DNA comes through to make pores ELECTROPORATION DEFINITION: technique that uses an electric field to increase the permeability of cell membranes, allowing DNA or other substances to enter the cells; it can involve recipient cells taking up fragments of dead cells through a process called "natural transformation," where they scavenge for DNA from their environment. = Horizontal gene transfer
28
Transduction
- occurs when bacterial phages (which are DNA carriers from donor to recipient) transfer DNA from 1 bacteria to another - Virus incorporate DNA fragments from host cell: - if DNA fragments are homologs * bacteria becomes partial diploid - Recombination by double crossovers = Horizontal Gene transfer
29
3a. Generalized Transduction
1) phage attachment 2) phage enzymes: releases enzymes to poke holes 3) phage DNA replication: viral enzymes will cut up bacterial chromosome wants to take the energy to build more self-viruses RECOMBINATION CAN OCCUR 4) phage proteins: reconstruct bacteriophages 5) phage assembly 6) phage release: phage removed to infect new bacterial cells *a piece of bacterial chromosome is put in* - stats alive but on another molecule to reproduce and recombine
30
3b specialized Transduction
Viral DNA is brought in, and could stay is living cell and lysogenic cycle *can also go Dormant to make no viral products* Prophage - will grow and divide (multiply DNA by separation) - continue to reproduce the viral chromosome * Comes out of lysogenic cycle *
31
Virulent vs Temperate Bacteriophage
virulent bacteriophage - uses only lytic cell of infection - kill host bacteria temperate bacteriophage - uses both lysogenic and lytic cycle of infection - may or may not kill host bacteria prophage- bacteriophage integrated into host DNA
32
Genetic Recombination in Eukaryotes : Meiosis
- meiosis occurs in different places in organismal life cycles - meiosis changes both chromosome number and DNA sequence - meiosis produces 4 genetically different daughter cells - several mechanisms contribute genetic diversity
33
Sexual Reproduction
- produces offspring by union of male and female gametes (sperm and egg) - meiosis produces gametes with 1/2 chromosome number *gametes are genetically different* - evolutionary advantage: genetic shuffling
34
Fertilization
- fuses nuclei of egg and sperm = zygote - restores parental chromosome number
35
Animal Life Cycles
- diploid phase dominates 1) meiosis followed by gamete formation 2) haploid phase is reduced and short, no mitosis In Males=4 nuclei from meiosis form separate sperm cells In Females=only 1 nucleus becomes an egg
36
What must eggs have for zygote formation
large amount of cytoplasm because if its fertilized its ready to be divided to make macromolecules etc etc
37
Homologs Chromosome pairs
* paternal chromosomes from male parent * maternal chromosomes from female parent = sets are homologs to each other, their alleles may be different within homologs pairs
38
Meiosis 1
- recombination exchanges segments between homologues - produces two haploid cells with chromatids attached
39
alleles
version of 1 gene
40
Meiosis separates homologs pairs
before meiosis: diploid (2n) after meiosis: haploid (n)
41
Meiosis 2
- sister chromatids separate into separate cells - produces 4 recombined haploid cells
42
2 meiotic divisor produce
4 haploid non-identical nuclei
43
What are things that occur during meiotic cell cycle
1) prophase 1: sister chromatids condense into chromosomes 2) synapsis: pairing of homologs 3) tetrads: fully paired homologs 4) recombination: mixes alleles across tetrads
44
Prometaphase 1
- nuclear envelope breaks down - kinetochores (miroctubules) attach to polar spindles + (not directly) to chrosomes
45
Metaphase 1 and Anaphase 1
METAPHASE: - tetrads align on metaphase plate ANAPHASE: - homologs segregate move to poles (sister chromatids attached) for both: - Nondisjunction creates abnormal chromosome number *RANDOM ALLIGNMENT*, 1 pair of homologs doesn't dictate the arrangement of chromosome
46
Telophase 1 and Interkinesis
- No change in chromosome - spindle disassembles Interkinesis: the pause between meiosis 1 and 2 where no DNA replication occurs
47
Prophase 2, Prometaphase 2
- chromosome condense, spindles form - nuclear envelope breaks, kinetochores attach to microtubules
48
Metaphase 2
- chromosomes align on metaphase plate *independent arrangement*
49
Meiotic Cell Cycle
Anaphase 2 and Telophase 2 - spindles separate chromatids - spindles disassemble - new nuclear envelopes form * 4 GENETICALLY DIFFERENT HAPLOID CELLS FORM *
50
What is nondisjunction
- both members of pair of homologs chromosomes connect to spindles from the same pole - following anaphase, one pole then receives both copies of pair and the other pole receives 0 = gametes that have 2 copies of a chromosome AFTER FERTILIZATION: zygote has 3 copies of chromosome instead of 2 Ex. Trisomy 21 (seperation is inaccurate due to gametes)
51
Nondisjunction in plants
an irregular number of chromosomes can be beneficial
52
Sex Chrosomes in Meiosis
- gametes produced by female may receive either X (oogenesis) - gametes produced by males may receive either X or Y chromosome (spermatogenesis)
53
Meiosis and Mitosis compared
- both: similar cell divisions, meiosis divides twice - mitosis: 2 identical daughter cells (diploid) - meiosis: 4 genetically different cells (haploid) - premeiotic interphases similar to mitotic interphase (G1,S,G2) - chromosome copied into sister chromatids
54
GENETIC VARIABILITY
1) GENETIC RECOMBINATION 2) RANDOM SEGREGATED AT ANAPHASE 1 3) ALTERNATIVE COMBO AT ANAPHASE 2 4) RANDOM FERTILIZATION
55
Genetic recombination
- recombination (crossing over) key genetic shuffle of prophase 1 tetrads held together at synaptonemal complex: - 2 of 4 chromatids exchange alleles - chiasmata or crossovers are points of exchange
56
Crossing-Overs
- Occurs at random on CHIASMATA (synaptonomeal complex of proteins that keep the chromosomes back to back) - occurs between non sister chromatids where they just exchange segments of DNA
57
Synaptonemal Complex
- how homologs chromosomes are held together
58
Random segregation
- key genetic shuffle of metaphase 1 - each chromosome of a homologs pair may randomly end up at either spindle pole * Any combo of maternal and paternal chromosomes= segregated to gametes * - 2X number of possible combination
59
At Metaphase 1
- Chromosomes line up randomly
60
alternative combo at anaphase 2
- attachment of spindle to kinetochore on sister chromatids is random - therefore alignment is random - increased variation
61
random fertilization
random chance of male and female gamete forming zygote - meiosis allows randomness bc gametes are genetically different necessary for mendelian laws of inheritance
62
what happens to hydrogen bonds when DNA is separated
they are broken, forming templates to allow for precise replication of genetic material
63
How is DNA paired
by enzymes that separate H bonds of one double helix and allow the base to reassociate with bases in a homologus helix.
64
in some types of bacterial recombination, one of the participating cells Is what
DEAD
65
what were Lederberg and Tatum testing in essence
whether or not bacteria have a kind of sexuality in they reproduction process - they use E.Coli for their experiment to isolate two strains, where 1 strain could grow only with biotin or methionine and the other didn't need biotin or methionine but needed leucine, thiamine, and theorenine. When they were mated they carried SOME protortophic alleles - some form of recombination between the DNA molecule of the two parental types must have produced the necessary combination with prototrophic alleles
66
T/F auxotrophs are mutant strands
T, and this is why they cant synthesize amino acids
67
What is Lederberg and Tatums experiment important for?
Antibiotic resistance -Lederberg's experiment showed that recombination in bacteria results from pre-existing genetic mutations, not from mutations induced by environmental factors -showing that resistant bacteria survive and reproduce when antibiotics are introduced.
68
What do bacterial cells do instead of fusing
Conjugate - make contact via long tubular sex pilus to make a cytoplasmic bridge
69
conjugation facilitates what
form of sexual reproduction in prokaryotic organisms
70
if the F plasmid is passed onto each daughter cell, its what type of inheritance If the F plasmid is copied and passed directly from the donor to recipient cell, its what type of inheritance
- VERTICAL - HORIZONTAL
71
How does F plasmid become part of main bacterial chromosome
- F plasmid gets near main chromosome and lines up in a short region of homology to undergo recombination - when 2 circular DNA molecules recombine they fuse into a larger circle
72
Is the integrated Plasmid with 1 cell or is it between the chromosomes of different cells
with 1 cell - meaning that after recombination the F plasmid is put into a cell ITS NOT put into the chromosomes of different cells
73
Why are Hfr cells called that
- high frequency cells - because they can promote recombination of DNA between cells by exporting copies of chromosomal genes to another cell
74
What happens when the F plasmid is integrated into the bacterial chromosome
- genes are still available for expression - therefore, Hfr cells make sex pili and can conjugate with an F- cell
75
Difference between F plasmid transfers alone than when Hfr cells transfer genetic material
F plasmid: recipient cells become F+ with the plasmid Hfr: origin of transfer is near the middle of the integrated F plasmid, so only 1/2 of the total F plasmid DNA is transferred at the front of the other 1/2 of F plasmid {BECAUSE SEX PILUS BREAKS BECAUSE INTEGRATION OF F FACTOR MAKES PILUS FORMATION PRONE TO DISRUPTION} - therefore the cell will become a partial diploid
76
What happens to incoming alleles that are not recombined onto the chromosome
they're lost
77
what do transcription and transduction allow for that conjugation doesn't
enables recipient cells to recombine with DNA obtained from dead donors
78
What can a mistake in the infection cycle cause
transfer of bacterial genes from a donor to a recipient cell
79
What is a prophage essentially
- state of phage (virus) integrated into host chromosomal DNA
80
What is specific to specialized transduction
In specialized transduction, only bacterial genes near where the phage inserted itself in the bacterial DNA are mistakenly included in the phage DNA due to a recombination error. THE ERROR: phage DNA incorrectly cuts out, taking nearby bacterial genes with it.
81
Two kinds of Differences with Meiosis
- halves chromosome number - new combinations of alleles arising from recombined DNA sequences
82
Different alleles of a given gene have similar
BUT DISTINCT DNA SEQUENCES - Therefore they likely encode different variations of RNA or proteins
83
Differentiate between CHROMATIN CENTROMERE SISTER CHROMATIDS CHROMOSOME
CHROMATIN - stuff chromosomes are made from: nucleic acid + proteins CENTROMERE - structure that helps chromosome get oriented during cell division and hold SC together SISTER CHROMATIDS - evident after chromosome replicates its DNA CHROMOSOME - joined sister chromatids are part of one chromosome
84
How can we determine the number of chromosomes a cell can have
count the number of centromeres - two of each type of chromosome are found in a cell-diploid - one of each-haploid
85
T/F Chromosomes pair up during mitosis
F
86
What happens when homologs chromosomes are paired
chromatids physically exchange segments
87
the synapotmeal complex is a
protein framework - it disappears when exchange is complete towards the end of prophase 1
88
spindle attachment during mitosis vs meiosis
MITOSIS: spindle fibers attach to centromeres of sister chromatids MEIOSIS: spindle fibers attach to homologous chromosomes during meiosis I and sister chromatids during meiosis II.
89
T/F cells from meiosis directly enter cell duplicating again
F, they produce reproductive cells
90
the nucleus will have (at start of meiosis)
1/2 the number of chromosomes present in meiocyte that began meiotic division
91
why is it hard for humans to produce genetically identical offpsirng
- so much variability introduction by recombination and juggling at DNA - TWINS: - arise from mitotic division of.a fertilized egg
92
genetic variability arrives from 4 sources
1) genetic recombniation betwn homologs chromosomes 2) differing combinations of mom and dad chromosomes segregated to poles during anaphase 3) differing combinations of recombinant chromatids segregated to the poles 4) sets of male and female gametes that unit

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