GENE LINKAGE Flashcards

1
Q

WHAT IS GENE LINKAGE?

A

the genes are located on the same chromosome and their alleles have a tendency to be inherited together
-exception to Mendelian genetics (against independent assortment)
-always more genes than chromosomes, therefore, not all genes undergo independent assortment

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2
Q

DEFINE HAPLOTYPE

A

combination of alleles which are inherited together
-every human has 2 haplotypes of any autosomal region (1 from mother, 1 from water)
-a whole single haplotype is always passed to gamete

EG: example - Y chromosome or MHC complex on 6p21.3 (codominant gene in complete linkage)
-men are hemizygotes for characteristics coded on non-homologous regions of Y
chromosomes
-Y-haplotype is identical from father to son, which is used is genealogic studies à we
can examine the inheritance of Y chromosome through centuries

EG: MHC complex on chromosome 6 (6p21.3)
-divided into 3 classes
-very polymorphic
-codes for glycocalyx recognizing non-self structures

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3
Q

WHAT HAPPENS DURING COMPLEX LINKAGE?

A

genes are so close to each other that they dont segregate during crossing over
-only combinations of alleles which are also present in parents

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4
Q

WHAT ARE THE POSSIBILITIES OF P IN A DIHYDRIDE CROSS?

A
  • cis (coupling) AABB x aabb
  • trans (repulsion) AAbb x aaBB
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5
Q

EXPLAIN THE F1 GENERATION OF A DIHYDRIDE CROSS?

A

form only two types of gametes with non-recombined alleles
-1:1

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6
Q

EXPLAIN THE F2 GENERATION OF A DIHYDRIDE CROSS?

A

genotypic ratio 1:2:1
phenotypic ratio is 3:1 or 1:2:1

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7
Q

EXPLAIN THE RESULT OF A DIHYDRIDE BACKCROSS?

A

always having a phenotypic and genotypic ration of 1:1 = LINKAGE
- F1 (heterozygote) x recessive homozygote: AaBb x aabb -> phenotypic and genotypic ratio is the same

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8
Q

WHAT IS INCOMPLETE LINKAGE?

A

individual genes are on the same chromosomes but so far apart that they can be separated through recombination / crossing over
-maximal probability of recombination is 50%
-frequency of crossing-over is directly proportional to the distance between genes

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9
Q

WHAT IS THE PURPOSE OF CROSSING OVER DURING PROPHASE 1?

A

gametes with a set of alleles that are in gene linkage, and which is different from the parental set, are created when there have occurred a recombination between the alleles

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10
Q

DISCUSS THE MONOHYBRID PATTERN OF LINKED GENES

A
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11
Q

HOW DOES F1 OF DIHYBRID IMCOMPLETE LINKAGE LOOK?

A
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12
Q

HOW DOES F2 OF DIHYBRID INCOMPLETE LINKAGE LOOOK?

A
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13
Q

WHAT ARE THE POSSIBLE PARENTAL AND RECOMBINANTS OF DIHYBRID CROSS?

A
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14
Q

IS THERE A DIFFERENCE BETWEEN CIS AND TRANS RATIOS IN B1?

A

yes
INCOMPLETE LINKAGE

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15
Q

HOW IS GENE STRENGTH MEASURED?

A

based on the number of recombinant and non-recombinant offspring in the analytical (test) backcross – B1

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16
Q

WHAT IS MORGANS NUMBER?

A

p = recombinant frequency / whole population

p = 0 (complete linkage)
p = 0.5 (free assortment)
1cM = 1% frequency of recombination

17
Q

WHAT IS BATESONS NUMBER?

A

measures how many times more probable it is for the formation of non-recombinant gametes when compared to recombinant ones

c = non recombinant / recombinant
always = 1 (independent assortment) < c < infinity (complete linkage)

18
Q

IS IT POSSIBLE TO HAVE MORE RECOMBINANT GAMETES THAN PARENTAL GAMETES?

A

no
there are always more non-recombined gametes than recombined

19
Q

WHAT ARE THE FACTORS THAT AFFECT GENE LINKAGE STRENGTH?

A

1- multiple crossing over
2 - interference
3 - absolute linkage
4 - pseudoallelism

20
Q

WHAT IS THE RATIO OF A B1 CROSS THAT HAS NO LINKAGE?

A

1:1:1:1

21
Q

HOW MANY cM EQUALS COMPLETE LINKAGE?

A

0

22
Q

HOW MANY cM EQUALS NO LINKAGE?

A

50

23
Q

HOW MANY cM EQUALS INCOMPLETE LINKAGE?

A

any other number