Genetics-Gene Identification Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

What are the two ways we can identify diseased genes?

A

1) Functional cloning: knowledge of the protein function helps you find the gene. 2) Positional cloning: map the disease, find the gene and then figure out the function of the protein.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What percent of the human genome actually codes for protein?

A

1.5%. The rest is involved in control of regulation of gene expression.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What percent of the human genome is actually transcribed?

A

80.00%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Although humans don’t have very many genes, what allows us to have a lot of variation?

A

Splicing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a genetic marker?

A

Polymorphic site that has a sequence difference between two or more gene alleles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the most common genetic markers?

A

1) SNPs (single nucleotide polymorphisms) and SNVs (single nucleotide variants, which included polymorphisms, deletions and insertions) 2) Microsatellites (simple sequence repeats) 3) Restriction fragment length polymorphisms (RFLPs, restriction enzyme sites)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a genetic linkage?

A

Physical linkage of two genes located on the same chromosome that are inherited together.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the 3 patterns of gene segregation?

A

Independent assortment, linkage of loci close together on same chromosome and recombinate gametes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What determines the frequency of recombination between two linked loci?

A

Recombination fraction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How do you know this was the recombinant gene?

A

All of the other children have a B if they have an A or a b if they have an a. This last child has a b with an A. Crossing over must have happened. Recombination fraction is 0.1.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Recombinant fraction if no recombination occurs

A

0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Recombinant fraction if the loci are unlinked

A

0.5, there is a 50% chance of any allele pairing with the other.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What method do we use to describe genetic linkages?

A

LOD scores (log of the odds).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What LOD score is the threshold for favoring odds of linkage?

A

Z > 3 (odds of being linked are 10^3, or 1000x > than odds of not being linked)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How is recombination frequency determined?

A

By the distance two genes are away from each other, the closer they are, the lower the recombination frequency. Note that 1 centiMorgan = 1% or in 100 meiotic divisions, 1 will become recombinant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

On average, what is the distance of 1cM?

A

1 centiMorgan is about 1 Megabase pair

17
Q

How do we map disease genes by linkage analysis?

A

1) Enroll affected families 2) Determine disease status of each family member 3) Determine genotypes at set polymorphic markers across genome 4) Look for correlation between your markers and disease status

18
Q

Did the C allele in the Huntingtin study cause disease?

A

No, although 22 out of 24 people with Huntingtin disease had the C allele, it does not mean it caused disease. It means that the gene that caused disease is located near the C allele. Hence, people who do not have a family history of Huntingtin disease, but do have the C allele are not at risk for Huntingtin’s.

19
Q

This is a family with Huntingtin disease. The family wants to know the status of the fetus. The family was genotypes for the G8 locus which only has A and B alleles. What is the chance of II-1 to inherit disease? What is the risk the father has the disease? What is the chance the baby is affected? What is the total chance the fetus inherits the disease?

A

1) 50% 2) 0%, he is unaffected, despite B allele, he is not in the family line 3) 3%, A came from the mom and B came from the dad. Although A is unaffected, G8 and the Huntingtin allele are 3cM apart = 3% chance of recombination. 4) Chance inherits disease allele from mom (1/2) x chance of recombination (3/100) = 3/200 = 1.5%.

20
Q

What is a haplotype?

A

A set of linked polymorphic alleles that can occur in different combinations across two separate chromosomes. For this person the possible haplotypes are abc, abC, aBc, Abc, ABc, AbC, aBC and ABC (3 genes = 2^3 = 8 types)

21
Q

How do you know haplotypes are in linkage equilibrium?

A

The percentage of each haplotype is predictable from the individual allele frequencies.

22
Q

How do you know haplotypes are in linkage disequilibrium?

A

Assortment of haplotypes is not random and there may be many more haplotypes of the original founders.

23
Q

Why do we care about haplotypes?

A

If a particular haplotype occurs more frequently in affected individuals, a gene contributing to the disease may be located within the haplotype (between b and c shown below)

24
Q

What is responsible for a mosaic structure of haplotypes (haplotype blocks) in chromosomes over time?

A

There are recombination hotspots where recombination usually occurs and spots where it doesn’t really occur.

25
Q

What can you do to reduce the number of SNPs you are testing for in a study?

A

Figure out which haplotype block the gene is in and only test for a few SNPs within that block

26
Q

What is the difference between linkage analysis and association studies?

A

Linkage analysis are best for single gene disorders within families. Association studies are best for multifactorial diseases across different families.