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BIOL 311 > Chapter 4 & 5 > Flashcards

Chapter 4 & 5 Flashcards

1
Q

What are lethal alleles?

A

When 2 copies of the mutant allele are inherited then it is lethal for the organism.

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2
Q

What is penetrance?

A

The number of organisms that show the phenotype that associates with the genotype

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3
Q

What is expressivity?

A

The level of gene expression that results in a certain degree of the phenotype.

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4
Q

What factors impact penetrance?

A

1.) Environment
2.) Other gene influence
3.) Mutations

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5
Q

What are auxotrophs?

A

These are the necessary materials or mediums needed to make an organism, gene, or mutation grow.

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6
Q

What is the complementation test?

A

When there is a mutation that causes a loss of function for a phenotype, then there is a second mutation that causes a loss of function for another phenotype, if the 2 mutations double they can complement and result in the wild type phenotype if they are different genes if they are on the same gene then they cannot complement and lead to the wild type phenotype.

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7
Q

Summary of Complementation

A

Complement occurs when the alleles are on different genes and failing to complement occurs when the alleles are on the same gene.

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8
Q

What is epistasis?

A

This is when the phenotype of one mutation masks the phenotype of another.

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9
Q

What is a suppressor mutation?

A

This is when the mutation reveses the effect of the mutation in another gene back to wild type.

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10
Q

What are synthetic mutations?

A

These are mutations in 2 different genes that do cause a phenotype individually but together lead to a mutant.

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11
Q

What are the different methods to determine functional relationships between genes?

A

1.) Mutate
2.) Complementation Test
3.) Make a double mutation line

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12
Q

What to look for in a gene interaction?

A

For a gene interaction the 9:3:3:1 will be less and the 9:3:3:1 genotype is standard for no interaction in a dihybrid cross.

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13
Q

What are the 5 ratios?

A

1.) No interaction => 9:3:3:1
2.) Same pathway => 9:7
3.) Recessive epistasis => 9:3:4
4.) Dominant epistasis => 12:3:1
5.) Suppressor mutation => 13:3

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14
Q

Which level of phenotypic expression is quantitative?

A

Expressivity

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15
Q

Which level of phenotypic expression is qualitative?

A

Penetrance

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16
Q

What happens to the ratio of the genotypes and phenotypes when there is gene interaction?

A

The ratio decreases for a dihybrid it would decrease from 9:3:3:1 and for a monohybrid it would decrease from 3:1.

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17
Q

What is recessive epistasis?

A

This is when the phenotype of the recessive allele masks the phenotype of another allele.

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18
Q

What is dominant epistasis?

A

This is when the phenotype of the dominant allele specifically masks the phenotype of the other allele.

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19
Q

What is the normal ratio?

A

9:3:3:1

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20
Q

What is the ratio if the mutations are on the same gene?

A

9:7

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21
Q

What is the ratio for recessive epistasis?

A

9:3:4

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22
Q

What is the ratio for dominant epistasis?

A

12:3:1

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23
Q

What is a pleiotropic allele?

A

Alleles that are able to affect several properties of an organism.

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24
Q

What are the factors that impact expressivity?

A

1.) Environment
2.) The allelic constitution of the genome

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25
Q

When does the 9:3:3:1 occur?

A

This is the phenotypic ratio between 2 heterozygous organisms - F2 generation this is also expected when unlinked.

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26
Q

When does the 1:1:1:1 occur?

A

This is the phenotypic ratio between a heterozygous and a tester organism this is also expected when unlinked.

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27
Q

What are syntenic genes?

A

These are genes that are on the same chromosome.

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28
Q

What is the difference between a syntenic gene and linked genes?

A

For genes to be linked they have to be on the same chromosome but they have to be close enough to each other for independent assortment to be impacted.

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29
Q

What is the cis conformation?

A

This is when 2 of the same type of the alleles are on the same homolog or on the same chromosomes (for example 2 wild type or 2 mutant).

30
Q

What is the trans conformation?

A

This is when 2 different types of alleles are on the same homolog or on the same chromosome (for example 1 wild type and 1 mutant allele).

31
Q

What is the result on the gametes when there is no crossing over?

A

Only parental type gametes will form without crossing over.

32
Q

What evidence proves that crossing over or recombination takes place?

A

The chiasmata it is an X shape that forms when the tetrads in propase 1 are undergoing synapsis and then crossing over.

33
Q

What is the difference between synapsis and crossing over?

A

Synapsis is when 2 homologous chromosomes pair up and then crossing over is the recombination of genes.

34
Q

When is crossing over more likely to occur?

A

When the genes are further apart rather than closer together. Also, if you think of it as a dart board when you are looking at the bigger circle you are more likely to hit the board compared to when you isolate to a smaller circle.

35
Q

What is the recombinant frequency?

A

This represents the distance between the genes < 50% means linked genes, but > 50% means unlinked genes and each time the chromosomes are segregated the genes will maintain this RF distance and the units are cM.

36
Q

What can the recombinant frequency tell us about recombination?

A

That the percent calculated is the probability that crossing over will occur.

37
Q

What is a trihybrid cross?

A

A cross that looks at 3 traits.

38
Q

How do you find the total number of gamete possibilities?

A

2^(# of genes)

39
Q

How can you determine which gene is in the middle quickly?

A

Look at the parental phenotype and then the lowest recombinant and compare which ever allele is flipped that one is the middle gene.

40
Q

Why do the recombinant frequencies not add up?

A

Because we are assuming that only 1 crossing over event takes place however crossing over can occur in more than 1 place which we have to take into account in order for the distances to add up.

41
Q

How do you account for DCO?

A

By multiplying the 2 smallest categories by 2 and adding it to the total from the genes that are the furthest apart.

42
Q

Where are the double crossovers more likely to occur?

A

Between the genes that are the furthest away.

43
Q

Why are the DCO often overlooked?

A

This is because the they look like the parental phenotype so they are often forgotten.

44
Q

What type of crossovers will have an impact?

A

When there are an even number of cross overs the result of one cross over can be undone therefore the easiest to distinguish are odd numbers of crossing over.

45
Q

How do you calculate if the genes are linked if the parental phenotype class is unclear?

A

1.) Chi-squared test => Using unlinked as the null hypothesis
2.) The DF=1 method

46
Q

What is the degree of freedom = 1 method?

A

This method involves using the observed to calculate the interference and then the expected values and you end up using 1 value to calculate the rest therefore the DF=1 and this can be used when a complete dataset is not provided.

47
Q

What are the molecular pathways to crossing over?

A

1.) Double stranded break on the chromatids
2.) Continue to break a part of the chromatids to get to the 3’ region
3.) Invsasion and dispacement replacing the break with some of the non-sister chromatids
4.) Polymerization 3’=>5’ growth
5.) Heteroduplex regions are sealed off by ligase

48
Q

What does crossing over occur between?

A

During prophase 1 the homologous chromosomes undergo synapsis to form tetrads and pair up then non-sister chromatids undergo crossing over primarily. Sister chromatids can undergo crossing over but it’s rare and doesn’t lead to new allele combinations.

49
Q

What is interference?

A

This is finding out if one crossing over event is independent or dependent of another.

50
Q

How to determine the interference?

A

Take the 2 smaller recombinant frequencies multiply by the total and observe the rare phenotypic class if they are consistent they are independent but if they are different then there is interference.

51
Q

What is heteroduplex DNA?

A

When there is more than 1 mismatch nucleotide pair.

52
Q

What is a double stranded break?

A

When there is a clip in both strands of the DNA of the DNA helix which leads to crossing over this occurs due to the endonuclease enzyem which in yeasts is Spo 11. Also the phosphodiester bonds of both strands are clipped.

53
Q

What is eroding?

A

This is when the 5’ end of the chromatids break and leave the 3’ end exposed this allows for additions later on.

54
Q

How do the Holliday junctions form?

A

When the D-loop is enlarged by the new DNA synthesis at the 3’ end of the invading strand and is uses the displaced strand as a template.

55
Q

What is the Displacement or D-Loop?

A

When a single strand tail invades the non-sister chromatid and forms a stable heteroduplex.

56
Q

What is polymerization?

A

The other strand acts as a template for the old strand and polymerase comes in to generate the nucleotide sequences and during which the helix is being separated. Also the heteroduplex regions of both DNA are elongated.

57
Q

What is the holliday junction orientation when crossing over does not occur?

A

Both junctions are in the same direction.

58
Q

What is the Holliday junction orientation for crossing over to occur?

A

1 Junction that is up and down
1 Junction that is left and right

59
Q

What is the end product?

A

The chromatids have nicks which are sealed by DNA ligase and the strands have undergone crossing over. Thus the Holliday junctions or chiasma form.

60
Q

What was the experiment that Meselson and Weigle conducted in relation to crossing over?

A

They observed 2 genotypes in bacteriophages those that had light and heavy alleles. These bacteriophages then infected other E.Coli whch led to were a mix of light on heavy and heavy on light.

61
Q

Were there variations in the phenotype?

A

Yes, there was expressivity in the phenotype which varied based on how much of the region was light or heavy.

62
Q

What occurs in yeast when there is NO crossing over?

A

The ratio is 4:4 and in yeast the chromosomes were contained within the ascus which were anchored together so they had a specific orientation to them.

63
Q

What occurs in yeast when there is crossing over?

A

The ratio is 2:4:2 or 2:2:2:2 and in this case there is mixing among the chromosomes.

64
Q

How did the conculsion of allele conversion come about (frequent)?

A

The allele conversions were too common to be spontaneous so the rationale was that crossing over then had to occur.

65
Q

What is the ratio when the heteroduplex is not corrected?

A

Aberrant 3:1:1:3

66
Q

What is the ratio when one strand is corrected?

A

5:3

67
Q

What is the ratio when both strands are corrected?

A

6:2

68
Q

How do you determine if the genes had crossed over?

A

Compare what you started with before prophase to after if there is any change then crossing over occurred.

69
Q

What causes the allelic conversions?

A

The recombination event

70
Q

What results in the reciprocal products of recombination?

A

Breakage and repair

71
Q

Does recombination lead to a gain or loss of nucleotide pairs?

A

No, because there is a mututal exchange

72
Q

What does interference do?

A

It decreases the amount of double cross overs that can occur.

I = 1 - ((DCO Observed)/(DCO Expected))

BIOL 311 (12 decks)

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