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genetics > Linkage and Chromosome Mapping > Flashcards

Linkage and Chromosome Mapping Flashcards

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1
Q

linked genes

A

alleles at different loci travel together

they do not assort independently

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2
Q

complete linkage

A

when genes are close together and no crossing over occurs between them

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3
Q

What allows recombinant types to be produced?

A

crossing over

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4
Q

crossing over

A
  • occurs between non-sister chromatids of homologous chromosomes
  • occurs in pachytene
  • allows recombinant types to be produced
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5
Q

recombinant gamete types

A

gametes that arose due to a crossover

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6
Q

parental gamete types

A

gametes that are not a product of crossing over

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7
Q

Which type are more frequent: parental or recombinant?

A

parental

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8
Q

coupling phase

A

when one chromosome contains the dominant alleles for both loci and the other contains the recessive alleles for both loci

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9
Q

repulsion phase

A

when each chromosome contains both a dominant and recessive allele - heterozygous for both

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10
Q

recombination frequency

A

the frequency of crossing over between two genes

it is proportional to the distance between the genes

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11
Q

are there more crossovers between genes that are further apart or closer together?

A

far apart

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12
Q

map distance

A

numerically equal to the percentage of recombination between the loci

= (recombination frequency)(100)

1% recombination = 1 centimorgan

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13
Q

2 point mapping experience

A

you are trying to determine the distance between two linked loci

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14
Q

Steps to 2 point mapping

A
  • mate 2 pure-breeding individuals opposite in phenotype for the two loci in question
  • test cross F1
  • classify the testcross progeny into parental types and recombinant types
  • determine the map distance as percentage of progeny that were due to a recombination event between the two loci
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15
Q

If independent assortment occurs, then there should be…

A

an equal number of parental and recombinant types

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16
Q

Which would you expect when genes are linked?

  • # parental > # recomb
  • # parental < # recomb
  • # parental = # recomb
A

parental > # recombinant

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17
Q

Interpret a map distance of 13

A
  • there are 13 centimorgan between A and B loci
  • the probability of a crossover between the A and B loci is 0.13
  • 13% of the gametes from the heterozygous individual are expected to be the recombinant type
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18
Q

For map distances <25…

A

there is a nearly linear relationship between recombination frequency and actual distance

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19
Q

For map distances >25…

A

the percent recombination underestimates map distance

20
Q

What is the map distance that will show for independently assorting loci?

A

50 cM

21
Q

mapping function

A

a graph that shows the relationship between the percent recombination that we observe in an experiment and the actual map distance between genes

22
Q

Creighton and Morgan

A
  • crossing over does involve physical exchange between homologous chromosomes
23
Q

3 point map

A

looks at 3 genes on a chromosome

24
Q

Steps to 3 point mapping

A
  • create an individual heterozygous for 3 genes
  • test cross
  • pair up the data based on opposite characteristics - crossovers in the same location
  • Identify the NCO and DCO
  • determine gene order
  • rewrite F1 gametes in correct order
  • classify progeny based on type of cross over
  • determine map distance
25
Q

Testing for linkage in a 3 point test

A
  • complete chi square between each loci for independent assortment
  • find the parental types - those that are pure breeding and those that have the same phenotype combination as the pure breeding
  • if fail to reject with more parental, can assume linkage
26
Q

classes of crossover with 3 gene types

A
  • NCO - no crossing over
  • SC1 - cross over in left region of map
  • SC2 - cross over in right region of map
  • DCO - double crossover
27
Q

Determining gene order with 3 genes

A
  • Find NCO and DCO
  • write down both NCO
  • write down one DCO
  • circle the DCO alleles in the NCO
  • the allele circled alone is in the center of the map
  • rewrite both NCO with the correct allele in the center
  • put one NCO on the top and the other on the bottom
28
Q

coefficient of coincidence

A

determine if a cross over in one region affects the change of getting a simultaneous cross over in the other region or if the crossing overs are independent of each other

C = (Observed # DCO)/(Expected # DCO)

29
Q

interference

A

when number of observed DCO is less than expected, something “interfered” with crossing over

I = 1-C

30
Q

NCO

A

=1-any crossover
=1-SCO1-SCO2-DCO
=1-r1-r2+DCO

31
Q

SCO1

A

=r1-DCO

32
Q

SCO2

A

=r2-DCO

33
Q

DCO

A

=r1r2C

34
Q

ascus

A

the sac containing all products from the meiotic and mitotic divisions of Neurospora crassa

35
Q

describe how an ascus is form

A
  • Fertilization of haploid female and male occurs
  • both divisions of meiosis occur
  • a mitotic division occurs
  • all products are held together in one sac
36
Q

1st division segregation

A

when no crossover occurs in meiosis of Neurospora crass

4/4 pattern

37
Q

2nd division segregation

A

a crossover between gene and centromere occurs in meiosis of Neurospora crassa
there are 4 types of these patterns

38
Q

pedigree analysis

A

observe multiple families to find traits that are associated with each other by tracing them on pedigrees

39
Q

sendai virus

A

used to fuse mouse and human cells for synteny testing

40
Q

synteny test

A

used to locate human genes to their chromosomes
cell culture test so looking at enzymes, proteins not phenotypes
performed by fusing mouse and human cells

41
Q

synkaryon line

A

stabilized cell lines in synteny tests

contain a few human chromosomes and most if not all of the mouse chromosomes

42
Q

heterokaryon

A

a cell that has two nuclei

43
Q

GWAS

A
  • genome wide association studies
  • used to map human genes based on associations between phenotypic characteristics and molecular markers
  • can help identify small region of the chromosome to look for genes that have biological significance for our phenotype
44
Q

SNPs

A

single nucleotide polymorphisms
molecular marker most commonly used in GWAS
variations at a single base pair

45
Q

What do GWAS look at?

A

populations of individuals

not pedigrees or parent-child-family relationships

genetics (5 decks)

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