Review for Genetics Exam 2

What is recombination?

The exchange of genetic material between chromosomes. E.g. crossing over of chromosomes w linked genes

What is the relationship between map units and rate of recombinaton?

Directly proportional. Farther away means higher rate of recombination.

How do you find the map units between two chromosomes?

Examine the phenotypic ratio, transform into percentages. The percentage of total recombinant offspring is converted into map units.

What is the maximum distance threshold between two mapped linked genes? More than this number would mean unlinked genes.

50 mu

How do you determine the % of recombination of double crossovers?

Multiply the expected frequency of the two single crossovers

When looking at the gametes resulting from meiosis, the ones who maintained the original linkage are described as _____________, whereas the crossovers are described as _____________.

parental, recombinant

The presence of linkage violates which of Mendel's postulates?

independent assortment, because when linked the likelihood of one gene being assorted is changed (it is combined with another linked gene)

How do you determine recombination percentage for a cross?

subtract each real percentage from each expected percentage and average them

What is the general effect of linkage on genetic variation?

decreases

"Complete linkage" of two genes means what?

there is no crossing over.

Two genes that are found to be 55 map units apart are expected to show what % recombination?

independent assortment. no linkage

What are chiasmata?

The structures of chromosomes which wrap around each other during crossing over.

Other than map units, what other units could be used to describe the distance between linked genes on a chromosome?

centiMorgans (cM)

What did the Meselson-Stahl experiment demonstrate and what variable was used in this experiment?

Eukaryotic DNA replication is semi-conservative. 15N (heavy nitrogen) vs. light nitrogen 14N

What does ORI or OriC stand for? What is it?

Origin of replication. The particular sequence in a genome in which the replication fork/”bubble” is formed and replication is initiated.

What is needed in order to fill in DNA bases in replication?

3’OH group must be available for bases to be added.

What are all the major players involved in DNA replication and what do they do?

gyrase: remove supercoiling.

helicase: unzip DNA

ssbp: stabilize strands in open conformation

primase: add rna primers

polymerase: add bases to 3’ end

lygase: fuse leading and lagging strands together

Which type of chromosomal banding is used in karyotypes to create a striped pattern along each chromosome? Which type stains only the centromere?

G-banding, C-banding

Which amino acid begins all protein sequences?

Methionine (met)

What is the purpose of the 3’ poly A tail?

Stabilizes mRNA while it travels to destination

What is the purpose of the 5’ mG cap?

Signaling and directions to where it needs to go

Which part of a tRNA molecule is needed to match mRNA?

anticodon

If an mRNA molecule has a sequence of 48 bases, how many amino acids would be found in the resulting polypeptide?

15 (remove one because it’s the “stop” codon)

What type of enzyme is primase?

RNA polymerase

Which process is best associated with Okazaki fragments?

lagging strand DNA synthesis

Which polymerase is responsible for chewing through primers when they are no longer needed during DNA replication?

DNA polymerase I

What does degeneracy mean?

Several codons can code for the same amino acid.

Which type of mutation results in a premature stop codon signal?

nonsense

Which RNA Polymerase is used to create messenger RNA?

RNA Polymerase II

Which section of a tRNA molecule attaches to the amino acid?

'3OH end

Which site in the ribosome is the entry point for new tRNA molecules?

A site