Topic 4 Molecular Crossovef

Question 1

Meselson and stahl experiment

Answer 1

Two genotypes of phages one genotype heavy one light

Can see recombination if one got light or heavier

Question 2

Ascus contains what?

Answer 2

Products of a single meiosis

Question 3

What should the cross of two haploid fungi (neurospora crassa) that differ at a single gene yield

Answer 3

And ascus that has an equal proportion of each genotype (assuming no crossing over) 4 A : 4 a ratio after meiosis two than mitosis

Question 4

What should the cross of two haploid fungi (neurospora crassa) that differ at a single gene yield of recombination occurs

Answer 4

2 dark : 2 light : 2 dark : 2 light

Question 5

What is gene (allele) conversion

Answer 5

Crossing over within a GENE that causes aberrant (not expected) ratios

Question 6

What is heteroduplex dna

Answer 6

Mismatched region on dna that needs to be fixed to either the mutant sequence or WT sequence

Question 7

What are the ratios if heteroduplex region in neurospora is not corrected, if one strand correct, if two

Answer 7

3:1:1:3
3:5
2:6

Question 8

What is the double strand break repair model

Answer 8

First step is that one chromatid has a cut in its dna

One strand that is cut is degraded, and other single strand cut invades the non sister chromatid (forming a heteroduplex d loop)

The displaced other strand from d loop forms heteroduplex region with the other chromatid and this results in a Holliday junction