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BIOL 2104 > Midterm 2 > Flashcards

Midterm 2 Flashcards

1
Q

What is incomplete dominance?

A

One copy of the functional allele is not enough to completely make up for the nonfunctional one
Phenotypic ratios reflect genotype ratios
Red+white=pink flowers

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2
Q

What is codominance?

A

Shows both alleles

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3
Q

Explain how ABO blood types are an example of codominance

A

Type of molecules on cell indicate blood type
Can be A, B, or AB
A are AA or Ai and have A sugars
AB have both A and B sugars

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4
Q

Define allele frequencies

A

The percentage of the total number of gene copies for one allele in a population

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5
Q

Define monomorphic and polymorphic

A

Monomorphic: gene with one common wild-type allele
Polymorphic: more than one common allele

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6
Q

Define pleiotropy and give an example

A

Gene that affects more than one trait

Ex. Whites mutation in cats causes white coat, blue eyes, and deafness

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7
Q

What are recessive lethal alleles?

A

Allele that gives a viable phenotype in one dose
Lethal in 2 doses
Ex. Yellow lethal mutation in mice

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8
Q

What are Heath sensitive alleles?

A

Wild type phenotype at permissive temperature and mutant phenotype at restrictive temperature
Ex. Shibire mutation in dresophilia

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9
Q

Give an example of external environment affecting genetics

A

Phenylketonuria (PKU)
Autosomal recessive condition
Lost enzyme to convert phenylalanine to tyrosine
Can treat with low phenylalanine diet

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10
Q

How can two genes interact to determine one trait?

A
  1. Novel phénotypes can result from gene interactions eg. Seed coat in lentils
  2. Complementary gene action eg. Flower colour
  3. Épistasis eg. Dog fur
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11
Q

Define epistasis

A

The effects of an allele at one gene masking the effects of another gene

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12
Q

Explain how coat colour in labs is an example of epistasis

A

One gene for pigment synthesis (B= black, b=brown)
Second gene needed to transport pigment (action of e allele is to prevent pigment deposition in hairs)
Ie. e allele is masking, or epistatic to, the b gene being masked, or is hypostatic

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13
Q

What is recessive epistasis?

A

Epistatic gene must be homozygous recessive
Ex. Bombay phenotype when hh genotype is present for blood
9:3:4 ratio for unlinked

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14
Q

What is dominant epistasis I?

A

Epistatic gene must have at least one dominant allele present
The dominant allele of one gene masks both alleles of another gene
12:3:1 ratio

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15
Q

What is dominant epistasis II?

A

The dominant allele of one gene masks the dominant allele of another gene

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16
Q

Give the F2 ratios for the different gene interactions

A 
Four distinct: 9:3:31
Complementary: 9:7
Recessive epistasis: 9:3:4
Dominant epistasis I: 12:3:1
Dominant epistasis II: 13:3
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17
Q

What is complementary gene interaction?

A

One dominant allele of each of two genes in necessary to produce phenotype

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18
Q

What is the complementation test?

A

Functional test for allelism
Cross two mutants together and observe what happens
Can be applied only with recessive phénotypes

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19
Q

What can cause phenotypic variation for some traits?

A

Differences in penetrance and/or expressivity
Effects of modifier genes
Effects of environment
Pure chance

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20
Q

Define penetrance

A

The percentage of a population with a particular genotype that shows the expected phenotype
Can be complete or incomplete
Presence or absence of trait phenotype when carrying the genotype that confers that trait

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21
Q

Define expressivity

A

The degree or intensity with which a particular genotype is expressed in a phenotype
Differing strength of phenotype for same genotype

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22
Q

What do modifier genes do?

A

Alter the phénotypes produced by alleles of other genes

Can have major or subtle effects

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23
Q

What are the three key properties of genetic material?

A
  1. Replication: stores genetic information and accurately transmitted from parent to offspring
  2. Gene expression: material controls phenotype of the organism
  3. Mutable: must be able to change on rare occasion to allow for variation
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24
Q

What are the chemical constituents to DNA?

A

Deoxyribose
Phosphate
A nitrogenous base (CUT = pyrimidines)

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25
Q

What is a nucleoside? Nucleotide?

A

Side: base + sugar
Tide: phosphate + side

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26
Q

How is DNA attached?

A

Nucleotides linked in a directional chain

Phosphodiester bonds always form covalent link between 3’ carbon of one nucleoside and 5’ of next nucleoside

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27
Q

Describe complementary base pairing

A

Base pairs consist of hydrogen bonds between a purine and a pyrimidine
Each base pair has about the same shape

28
Q

What are some characteristics of the DNA double helix?

A

Polyanions (negatively charged)
Phosphoribose backbone toweards aqueous environment
Helix core excludes h2o
Base pairs at centre of helix
Successive base pairs stacked
Abtiparallel orientation of complementary strands
Strands held together by interchain H-bonds
Complementary base pairing results in specific association of the two chains of the double helix

29
Q

Describe DNA replication

A

Strand separation followed by coping of each strand
Each separated strand acts as a template for the synthesis of a new complementary strand
Base pairing dictates accurate replication of DNA double helix

30
Q

What does DNA polymerase do?

A

Replicates DNA in a 5’ to 3’ direction only

Only adds deoxyrubonucleotides to the 3’ end using single strand of DNA as a template

31
Q

Describe the initiation of DNA replication

A

Begins at the origin (ori) of replication
Initiation protein binds to ori
Helicase unwinds the helix
Two replication forks are formed
SSBP keep helix open and primase synthesizes rna primer
Primers are complementary and antiparallel to each strand

32
Q

What direction does DNA replication go in?

A

Bidirectional

Begins at one of more origins of replication

33
Q

Describe elongation

A

Correct nucleotide sequence in copied from template strand to newly synthesize of DNA
DNA polymerase III catalyzed phosphodiester bond formation between adjacent nucleotides
DNA polymerase I replaces rna primer with DNA sequence
DNA ligase covalently joins successive Okazaki fragments together

34
Q

Define leading and lagging strand

A

Leading: continuous synthesis
Lagging: discontinuous

35
Q

Define Okazaki fragment

A

Short DNA fragments in lagging strand

36
Q

How is the lagging strand replicated?

A

Semi discontinuous

  1. Primase synthesizes short rna oligonucleotides copied from DNA
  2. DNA polymerase III elongates rna primer with new DNA
  3. DNA polymerase I removed rna at 5’ end of neighbouring fragment and fills gap
  4. DNA ligase connects adjacent fragments
37
Q

What does DNA gyrase do?

A

Removes extra twists
If DNA is circular, positive suoercoils must be introduced, one for each turn of the helix unwound
DNA gyrase introduces negative super coils

38
Q

What is a replisome?

A

Two DNA pol III enzymes replicating leading and lagging strands simultaneously

39
Q

What are telomeres?

A

Ends of DNA would get progressively shorter each round of synthesis
Telomerase maintains telomere length

40
Q

What are ribonucleoproteins?

A

Rna component serves as a template for synthesis of telomeric repeats at DNA ends

41
Q

How are telomeres, aging and cancer related?

A

Most normal somatic cells lack telomeres
Somatic cells have a limited number of doubling (20-60)
Gremline cells, stem cells, and unicellular eukaryotes have high telomerase activity and are therefore essentially immortal as are cancer cells

42
Q

Define forward mutation

A

Changes wild type allele to a different allele (change of phenotype in this case)
Ex. A+ to a

43
Q

Define reverse mutation (reversion)

A

Changes a mutant allele back to wild type (change in phénotype)
Ex. a to A+

44
Q

What are the 4 types of mutations?

A

Point mutations
Deletions or insertions
Inversions
Epigentic

45
Q

What are the two types of point mutations?

A

Transitions: purine to purine or pyrimidine to pyrimidine
Tranversions: purine to pyrimidine

46
Q

Describe insertions and deletions

A

Usually 1 bp, but can be much bigger

47
Q

Describe inversion

A

180 rotation of a segment of DNA (small or big)

48
Q

Define epigenetic

A

DNA sequence itself is unchanged

49
Q

What are the two types of large scale chromosomal mutations?

A

1) change in chromosome structure

2) change in chromosome number

50
Q

Define germ line cells and somatic cells

A

Germ line cells: give rise to gametes (mutations are transmitted to the progeny)
Somatic cells: all non-germ line cells (mutations only affect descendants of that cell, not progeny)

51
Q

Describe the replica playing technique

A
  1. Invert master plate, pressing against velvet surface leaves an imprint of colonies. Save plate
  2. Invert second plate with penicillin in medium, pressing against velvet surface picks up colony imprint
  3. Incubate plate
  4. Only penicillin resistant colonies will grow. Compare with position of colonies on original plate
52
Q

What is depurination?

A

One human cell losses ~1000 purines/hour

If not fixed to DNA replication, a random base is introduced opposite the apurinic site

53
Q

What is deamination?

A

C to U

T to A

54
Q

What are some sponanteous mutations that can alter DNA sequences?

A 
Depurination
Deamination
Deletions from naturally occurring radiation
UV light produces thymine dimers
Oxadative damage
55
Q

How does UV light produce thymine diners?

A

Halts replication fork, if normal repair system is overwhelmed, then an error prone repair system kicks in to bypass the stall by adding random nucleotides

56
Q

What are some sources of accuracy in replication?

A

Balanced levels of dNTPs
Polymerase reaction is highly accurate (conformational changes in active site core)
3’ to 5’ exonuclease activities of replicases
Battery if wnzyme repaire systems

57
Q

By what mechanism can mutations be induced?

A
  1. Radiation produce deletions and point mutations
  2. Replace a regular base in DNA with an analog that has altered base pairing properties
  3. Chemically alter a regular base in DNA so that is midpoints with another base
  4. Alter base stacking with intercalculating agent (proflavin, acridine orange) causing insertions/deletions
58
Q

What type of molecular changes might be responsible for a mutation that cannot be induced to revert?

A
  1. Deletion of a gene
  2. Mutation nucleotide substitutions in the gene
  3. Complex DNA rearrangement with more than one breakpoint in the gene
59
Q

What are some DNA repair mechanisms?

A
  1. Proofreading mechanisms of DNA polymerase
  2. Methyl-directed mismatch repair
    3 enzymatic reversal of DNA base alterations
  3. Base excision repair
  4. Nucleotide-excision repair
  5. Translesion DNA synthesis - error prone (SOS system)
  6. Repair of double-strand breaks (non-homologous end-joining)
60
Q

What are the steps to forward genetics?

A
  1. Varient phenotype: natural variation or induced mutation, screen for phenotype
  2. Make cross between strains: back cross of complementation cross (# of genes involved)
  3. Careful analysis of alterations in cellular processes: alteration in biochemical, physiological, cell biology and/or developmental processes, gene interactions
  4. Gene mapping and cloning: molecular analysis of gene and biochemical analysis of gene product
61
Q

What occurs with the complementation test if different genes?

A

F1 hétérozygote makes functional product for both genes

The mutations rescue of complement each other to give wild type phénotypes

62
Q

What occurs with the complementation test if same gene?

A

F1 hétérozygote make no functional product for gene 1

Gives mutant phenotype

63
Q

What are some types of mutagens?

A

Chemical mutagens: point mutations - affect proteins through truncation or replacement of key amino acids
Radiation - leads to small or large deletions of DNA or even chromosome breakage and rearrangements
Insertional mutagens: mutagenize genes by sticking a large chunk of DNA in the middle of it or its regulatory sequence

64
Q

Define selection

A

Only the desired mutants survive
Easy to screen large numbers
Limited to specific types of genes/roles

65
Q

Define screening

A 
Analyze all individuals
Give greater range of phénotypes 
Allow to identify unexpected phénotypes
More work than selection
Screening can be easy of laborious
66
Q

Define prototroph and auxotroph

A

Prototroph: wild type strain that grows in minimal media without nutritional supplements
Auxotroph: mutant strain that cannot grow in minimal media

BIOL 2104 (2 decks)

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