FIRST MIDTERM

Question 1

Compare c value and n value contained in a cell.

Answer 1

C-value refers to the amount of DNA usually measured in base pairs.
N-value refers to the number of chromosomes found in the haploid cell

Question 2

Differentiate haploid and diploid cells.

Answer 2

Haploid cells contain a single set of unpaired chromosomes, while diploid cells contain a homologous pair of every chromosomes.

Question 3

What are bivalents?

Answer 3

Homologs pairing during Prophase I

Question 4

What does crossing over mean?

Answer 4

Physical exchange of DNA b/w nonsister chromatids of homologs

Question 5

What is a ter sequence?

Answer 5

Ter sequence refers to the termination sequences located opposite of the origin sequence

Question 6

What is the function of the TUS protein?

Answer 6

TUS protein recognize and bind ter sequence and prevents further opening of the replication fork

Question 7

What are ORCs?

Answer 7

ORCs are origin recognition complexes which bind origin of replication. They recruit DNA polymerase.

Question 8

What does the PULSE-CHASE experiment involve?

Answer 8

PULSE = exposure and incorporation of a labelled reagent
CHASE = removal of labelled reagent from medium

Question 9

What are nucleosomes?

Answer 9

DNA wrapped around proteins called histones

Question 10

What is the function of CAF1?

Answer 10

• Delivers new histones to replicated DNA (need to double the amt of histones)
  
  • Recognizes PCNA (a processivity factor of DNA pool)

Question 11

Differentiate between condensins and cohesins.

Answer 11

Condensins bundle chromatids while cohesins link sister chromatids together.

Question 12

What are telomeres?

Answer 12

Telomeres are repeated sequences found at the end of linear chromosomes, they are non-coding DNA and do not have coding information.

Question 13

What are telomerase?

Answer 13

Telomerase are enzymes that extends telomeres by adding short repeats to the 3’ end of the chromosome using a small RNA template

Question 14

What are operons?

Answer 14

A set if coordinately controlled genes. In prokaryotes, they are gene clusters where several genes lie in tandem and are governed by the same promoter and the same inhibitory and stimulatory mechanisms

Question 15

Differentiate exons and introns.

Answer 15

Exons are expressed or the coding region while introns are the intervening sequence or the noncoding region.

Question 16

What are positive regulators and give an example.

Answer 16

Proteins that bind DNA and promote transcription.

MyoD in eukaryotes binds to DNA and turns on transcription. It recognizes specific sequence in minor groove.

Question 17

What are negative regulators?

Answer 17

Negative regulators are proteins that bind DNA and prevent transcription.

Question 18

How does Lac I work?

Answer 18

Lac I is a heterodimer that binds to DNA and represses lac operon expression by:

• preventing RNA polymerase from associating with promoter
• by preventing RNA polymerase from moving down the DNA

Question 19

How are operons regulated in prokaryotes?

Answer 19

Operons are transcribed as a single mRNA with multiple coding regions. They are regulated at the OPERATOR where the cell can sense different environment cues to turn on or off the operon.

Question 20

What happens to the lac operon in the absence of lactose in prokaryotic cells?

Answer 20

In the absence of lactose, Lac I binds to the operator and the transcription is blocked.

Question 21

In the presence of lactose, what happens to Lac I?

Answer 21

Lactose is an allosteric inhibitor of Lac I. In its presence, Lac I loses its regular shape making it unable to bind to the DNA and inhibit lac expression. Therefore, Lac Z, Y and A are now expressed.

Question 22

What is the difference between genotype and phenotype?

Answer 22

Genotype is all of an organism’s genes/DNA, while phenotype is the expression/manifestation of genotype.

Question 23

What is the difference between cis-acting and trans-acting mutations?

Answer 23

Trans-acting mutations: can act on sites other than the DNA molecule on which the mutation is located. Generally, these are genes for products (Proteins or RNAs) that can influence the expression of other genes or interact with the products of other genes.
Cis-acting mutations: only affects sites located on the same DNA molecule as the mutations. They do not code for gene products but are sites that can influence nearby gene expression. (E.g. Mutations on the promoter)

Question 24

Explain the logic of arranging genes in an operon.

Answer 24

Operons are arranged so that one regulatory event can control the expression of several genes that are required normally in the same pathway. Operons are regulated by having an operator region that controls a set of genes upstream of the transcription start site.

Question 25

Why do eukaryotes do not organize genes like how prokaryotes organize theirs in an operon?

Answer 25

Multicellular organisms often have different requirements for different regions in their genes, therefore co-regulating would be a waste of energy. Eukaryotes have introns and more complicated gene structure that does not make them amenable to polycistronic messages.

Question 26

What is a genetic locus?

Answer 26

A sequence in the genome that gives rise to a testable phenotype

Question 27

What is the difference between homozygote and a heterozygote?

Answer 27

``` Homozygote = organism with identical alleles at the gene of interest Heterozygote = an organism with different alleles at a gene of interest ```

Question 28

What is a wild type allele?

Answer 28

Commonly accepted normal form in a genetic organism

Question 29

What does haplosufficient mean?

Answer 29

One copy of an allele is sufficient for full phenotype

Question 30

If mutant allele is RECESSIVE, the wild type allele is ____________.

Answer 30

Haplosufficient. This means one copy of wild type allele is sufficient to give wild type phenotype.

Question 31

If mutant allele is DOMINANT, wild type allele is ____________.

Answer 31

Haploinsufficient. This means that one copy of wild type allele is NOT sufficient to give wild type phenotype.

Question 32

What are Mendel's conclusion about inheritance after his research?

Answer 32

1. Existence of genes 2. Genes are in pairs 3. Dominance vs. Recessiveness 4. Halving of gene pair in gametes 5. Equal segregation 6. Independent assortment

Question 33

What is a monohybrid cross?

Answer 33

A cross between two individuals identically heterozygous at one gene pair.

Question 34

What does true breeding mean?

Answer 34

A group of identical individual organism that always produce offspring of the same phenotype as the parents.

Question 35

What is a test cross?

Answer 35

A cross of individual organism of unknown genotype with a tester. This is done to a) determine the genotype of an unknown individual or b) test linkage.

Question 36

What is a tester?

Answer 36

A tester is an individual organism homozygous recessive for all alleles being tested.

Question 37

How does law of segregation tie in with our understanding of meiosis?

Answer 37

Alleles segregate in anaphase I (and it's a 50/50 chance) | Each gamete gets one allele

Question 38

What does Mendel's First Law state?

Answer 38

The two members of a gene pair segregate from each other into the gametes so half the gametes carry one member of the pair and the other half of the gametes carry the other member of the pair.

Question 39

What is a dihybrid cross?

Answer 39

A cross between two individuals identically heterozygous at two loci.

Question 40

Mendel's Second Law states that:

Answer 40

Unlinked or distantly linked segregating gene pairs assort independently at meiosis.

Question 41

What is a reciprocal cross?

Answer 41

A reciprocal cross is when you swap sexes of the parentals to determine if a gene is on an X-chromosome. This performed when you want to determine of the gene is sex-linked.

Question 42

What are auxotrophs?

Answer 42

Organisms that cannot grow on minimal media and they can only grow when minimal media (MM) is supplemented with a specific substance. Also called "metabolic mutants".

Question 43

What are prototrophs?

Answer 43

Prototrophs are organism that will grow on minimal media.

Question 44

What does a minimal media (MM) contain?

Answer 44

Lab growth media containing a sugar, inorganic salts + water.

Question 45

What does Complementation mean?

Answer 45

The production of a wild type phenotype when two different recessive mutations are combined in a diploid or heterokaryon.

Question 46

Explain the logic behind the complementation test.

Answer 46

In crossing two mutant lines, if heterozygote shows mutant phenotype, then the 2 mutations are within the same gene type (i.e. If they do not complement, they're allelic). If heterozygote shows wild type phenotype, then 2 mutations are in a different gene (i.e. if they complement they are NOT allelic).