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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
Q

Why isn’t the full chromosome not always sent

A
  • 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

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24
Q

Mapping genes by conjugation

A
  • 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

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25
Q

The order and time at which genes were transferred

A

able to map and assign relative positions of several genes of E. coli chromosome

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26
Q

Transformation

A

occurs when bacteria take up DNA from disintegrated bacteria
- linear fragments recombine by double crossing
- transformation bacteria usually have DNA protein in wall

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27
Q

Artificial transformation (part of transformation)

A
  • 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

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28
Q

Transduction

A
  • 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

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29
Q

3a. Generalized Transduction

A

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

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30
Q

3b specialized Transduction

A

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 *
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31
Q

Virulent vs Temperate Bacteriophage

A

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

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32
Q

Genetic Recombination in Eukaryotes : Meiosis

A
  • 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
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33
Q

Sexual Reproduction

A
  • 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
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34
Q

Fertilization

A
  • fuses nuclei of egg and sperm
    = zygote
  • restores parental chromosome number
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35
Q

Animal Life Cycles

A
  • 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

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36
Q

What must eggs have for zygote formation

A

large amount of cytoplasm because if its fertilized its ready to be divided to make macromolecules etc etc

37
Q

Homologs Chromosome pairs

A
  • 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
Q

Meiosis 1

A
  • recombination exchanges segments between homologues
  • produces two haploid cells with chromatids attached
39
Q

alleles

A

version of 1 gene

40
Q

Meiosis separates homologs pairs

A

before meiosis: diploid (2n)

after meiosis: haploid (n)

41
Q

Meiosis 2

A
  • sister chromatids separate into separate cells
  • produces 4 recombined haploid cells
42
Q

2 meiotic divisor produce

A

4 haploid non-identical nuclei

43
Q

What are things that occur during meiotic cell cycle

A

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
Q

Prometaphase 1

A
  • nuclear envelope breaks down
  • kinetochores (miroctubules) attach to polar spindles + (not directly) to chrosomes
45
Q

Metaphase 1 and Anaphase 1

A

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
Q

Telophase 1 and Interkinesis

A
  • No change in chromosome
  • spindle disassembles

Interkinesis: the pause between meiosis 1 and 2 where no DNA replication occurs

47
Q

Prophase 2, Prometaphase 2

A
  • chromosome condense, spindles form
  • nuclear envelope breaks, kinetochores attach to microtubules
48
Q

Metaphase 2

A
  • chromosomes align on metaphase plate
    independent arrangement
49
Q

Meiotic Cell Cycle

A

Anaphase 2 and Telophase 2

  • spindles separate chromatids
  • spindles disassemble
  • new nuclear envelopes form
  • 4 GENETICALLY DIFFERENT HAPLOID CELLS FORM *
50
Q

What is nondisjunction

A
  • 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
Q

Nondisjunction in plants

A

an irregular number of chromosomes can be beneficial

52
Q

Sex Chrosomes in Meiosis

A
  • gametes produced by female may receive either X (oogenesis)
  • gametes produced by males may receive either X or Y chromosome (spermatogenesis)
53
Q

Meiosis and Mitosis compared

A
  • 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
Q

GENETIC VARIABILITY

A

1) GENETIC RECOMBINATION

2) RANDOM SEGREGATED AT ANAPHASE 1

3) ALTERNATIVE COMBO AT ANAPHASE 2

4) RANDOM FERTILIZATION

55
Q

Genetic recombination

A
  • 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
Q

Crossing-Overs

A
  • 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
Q

Synaptonemal Complex

A
  • how homologs chromosomes are held together
58
Q

Random segregation

A
  • 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
Q

At Metaphase 1

A
  • Chromosomes line up randomly
60
Q

alternative combo at anaphase 2

A
  • attachment of spindle to kinetochore on sister chromatids is random
  • therefore alignment is random
  • increased variation
61
Q

random fertilization

A

random chance of male and female gamete forming zygote
- meiosis allows randomness bc gametes are genetically different necessary for mendelian laws of inheritance

62
Q

what happens to hydrogen bonds when DNA is separated

A

they are broken, forming templates to allow for precise replication of genetic material

63
Q

How is DNA paired

A

by enzymes that separate H bonds of one double helix and allow the base to reassociate with bases in a homologus helix.

64
Q

in some types of bacterial recombination, one of the participating cells Is what

A

DEAD

65
Q

what were Lederberg and Tatum testing in essence

A

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
Q

T/F auxotrophs are mutant strands

A

T, and this is why they cant synthesize amino acids

67
Q

What is Lederberg and Tatums experiment important for?

A

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
Q

What do bacterial cells do instead of fusing

A

Conjugate
- make contact via long tubular sex pilus to make a cytoplasmic bridge

69
Q

conjugation facilitates what

A

form of sexual reproduction in prokaryotic organisms

70
Q

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

A
  • VERTICAL
  • HORIZONTAL
71
Q

How does F plasmid become part of main bacterial chromosome

A
  • 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
Q

Is the integrated Plasmid with 1 cell or is it between the chromosomes of different cells

A

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
Q

Why are Hfr cells called that

A
  • high frequency cells
  • because they can promote recombination of DNA between cells by exporting copies of chromosomal genes to another cell
74
Q

What happens when the F plasmid is integrated into the bacterial chromosome

A
  • genes are still available for expression
  • therefore, Hfr cells make sex pili and can conjugate with an F- cell
75
Q

Difference between F plasmid transfers alone than when Hfr cells transfer genetic material

A

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
Q

What happens to incoming alleles that are not recombined onto the chromosome

A

they’re lost

77
Q

what do transcription and transduction allow for that conjugation doesn’t

A

enables recipient cells to recombine with DNA obtained from dead donors

78
Q

What can a mistake in the infection cycle cause

A

transfer of bacterial genes from a donor to a recipient cell

79
Q

What is a prophage essentially

A
  • state of phage (virus) integrated into host chromosomal DNA
80
Q

What is specific to specialized transduction

A

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
Q

Two kinds of Differences with Meiosis

A
  • halves chromosome number
  • new combinations of alleles arising from recombined DNA sequences
82
Q

Different alleles of a given gene have similar

A

BUT DISTINCT DNA SEQUENCES
- Therefore they likely encode different variations of RNA or proteins

83
Q

Differentiate between
CHROMATIN
CENTROMERE
SISTER CHROMATIDS
CHROMOSOME

A

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
Q

How can we determine the number of chromosomes a cell can have

A

count the number of centromeres
- two of each type of chromosome are found in a cell-diploid
- one of each-haploid

85
Q

T/F Chromosomes pair up during mitosis

A

F

86
Q

What happens when homologs chromosomes are paired

A

chromatids physically exchange segments

87
Q

the synapotmeal complex is a

A

protein framework
- it disappears when exchange is complete towards the end of prophase 1

88
Q

spindle attachment during mitosis vs meiosis

A

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
Q

T/F cells from meiosis directly enter cell duplicating again

A

F, they produce reproductive cells

90
Q

the nucleus will have (at start of meiosis)

A

1/2 the number of chromosomes present in meiocyte that began meiotic division

91
Q

why is it hard for humans to produce genetically identical offpsirng

A
  • so much variability introduction by recombination and juggling at DNA
  • TWINS:
  • arise from mitotic division of.a fertilized egg
92
Q

genetic variability arrives from 4 sources

A

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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