Lecture 10 - Linkage, Recombination, and Eukaryotic Gene Mapping

Question 1

What is meant by recombinant and nonrecombinant genes?

L10 S7;11

Answer 1

Recombinant:
-when the combination of alleles on a chromosome varies from the parent chromosome

Nonrecombinant:
-when the combination of alleles on a chromosome is the same as the parent chromosome

Question 2

For single crossovers, the frequency of recombinant gametes is half the frequency of crossing over because:

L10 S13-14

A. A test cross between a homozygote and heterozygote produces 1/2 heterozygous and 1/2 homozygous progeny
B. The frequency of recombination is always 50%
C. Each crossover takes place between only two of the four chromatids of a homologous pair
D. Crossovers occur in about 50% of meiosis

Answer 2

C. Each crossover takes place between only two of the four chromatids of a homologous pair

Question 3

What is the formula for calculating recombination frequencies?

L10 S15

Answer 3

Recombination frequency = (# of recombinant progeny / total # of progeny) x 100%

Question 4

What do the terms coupling and repulsion mean?

L10 S16

Answer 4

Coupling:
-one chromosome contains both of the wild-type alleles and the other contains both mutant alleles

Repulsion:
-both chromosomes contain a wild-type allele and mutant allele

Question 5

How does the map unit (or centiMorgan) relate to crossing over?

L10 S20

Answer 5

The crossover rate per map unit is 0.01 (1%) per generation

Question 6

Why can recombination frequency be used to map genes?

L10 S20-25

Answer 6

The closer genes are, the less frequently a crossing over even will occur between the genes to create a recombinant genotype

Question 7

How do you calculate coefficient of confidence and interference?

L10 S26-27

Answer 7

Coefficient of confidence = # of observed double crossovers / # of expected double crossovers

Interference = 1 - coefficient of confidence

Question 8

What are linkage disequilibrium and haplotypes? How do they relate?

L10 S30-31

Answer 8

Linkage disequilibrium:
-when genes segregate more or less than would be expected based off their actual distance

Haplotype:
-a set of alleles that tend to be inherited together, this can occur because they are actually located close enough that crossing over is uncommon or because they demonstrate linkage disquilibirum

Question 9

How did somatic-cell hybridization help to identify which chromosome a gene was on?

L10 S39-40;42-3

Answer 9

When human somatic cells are hybridized with mouse somatic cells certain human chromosomes will be eliminated.
You can identify which chromosomes remain and whether the gene products are present.
By doing this several times you can identify the common chromosome.

Question 10

What is GWAS?

L10 S57

Answer 10

Genome-wide Association Studies

Examination of genetic sequences to look for genome variants that are associated with a certain trait or disease.