Genetics Final Exam Section D

How do eukaryotic ribosomes identify which RNAs in the cell are mRNA, and therefore should be translated?

mRNAs have a 5' methyl G cap which the ribosome binds to

How is it that heterozygotes for recessive, loss-of-function mutations can have the same phenotype as homozygotes for the wildtype allele?

Half the amount of product can still fully complete the role of that protein in the cell, because it is not the rate-limiting step

How many SNPs does each person have, on average, compared to the "standard" human genome sequence?

5 million

Humans have more genes than any other species

False

Humans have the same number of protein coding genes as the nematode C elegans.

True

If someone is heterozygous for a wildtype allele and a non-functional mutant allele, what level of protein product will be present in the cell, compared to someone who is homozygous for wildtype alleles?

50%

Most of the RNA that is made in all cells is never translated.

True

Roughly how many protein coding genes does a typical, multicellular eukaryote have?

25,000

What defines the start of the open reading frame of a gene?

An AUG codon

You are looking at the genome sequence of an unknown individual and notice that one of their tyrosinase alleles has a mutation in the ORF that predicts a Glu to Ala change in its amino acid sequence. What effect will this have on the tyrosinase enzyme produced from this allele?

depends on the importance of that particular Glu in the tyrosinase enzyme

How many introns are there in the average human gene?

8

Strong promoters in E coli drive higher levels of transcription and usually show what feature?

Better match to the -35 and TATA box consensus

What binds to the TATA box of eukaryotes?

TBP

What is the function of sigma70 in E coli?

to identify a promoter, the +1 site, and which is the template strand

What is the key role of the branchpoint in splicing?

To bind to the first G in the intron

What protein binds to the -35 and -10 sequences in E. coli genes?

Sigma

Which of these describes how transcription is often terminated in E coli?

A stem-loop forms, causing the RNA polymerase to stall

Which of these is a good description of alternative splicing?

Including/excluding certain exons to generate a set of similar but distinct proteins

Which of these occurs during transcription of mRNA in eukaryotes?

\n addition of the methyl-G cap, Binding of TFIID to the promoter region, and removal of introns

What sequence is required to get the poly-A tail correctly added to eukaryotic mRNAs?

AAUAAA

Cystic fibrosis is due to an autosomal recessive mutation. If someone who has cystic fibrosis has children with someone who is a carrier (ie: heterozygous) what do you expect to see in their children?

50% will have CF

How many genes encoding miRNAs exist in multicellular genomes?

a few thousand

How similar are monozygotic twins?

Identical

If a red-green colorblind (sex-linked recessive) male who is also a carrier for a CF mutation (autosomal recessive) has children with a woman who is a carrier for a red-green colorblindness mutation, but homozygous for wild-type alleles of the CF gene, what will you see in their children?

\-half the males will be colorblind

or

\-no males or females will have CF

or

\-none of the above are true

If your great uncle (for example, your grandmother's brother) died of Tay-Sachs disease (autosomal recessive), what is the probability that you are a carrier of the same, mutant TS allele?

1/6

Mutations in the region encoding the 3' UTR of an mRNA would have the potential to disrupt what process?

binding of a miRNA guide

The human gene VAMP7 is pseudoautosomal. If a male who is a carrier for a VAMP7 mutation has children with a woman who is also a carrier for a VAMP7 mutation, what fraction of their progeny will show the VAMP7 mutant phenotype?

25%

What important function do the PAR1 and PAR2 regions of the X and Y chromosome serve in vertebrates?

allow them to pair up during meiosis in males

What is meant by the term "consanguineous" mating?

A mating between closely related people

Which of these is a good description of RISC?

It binds to a short sequence of RNA, which guides it to a target transcript

Flies with a mutation in the gene wrinkly have wings with ripples in them. Wrinkly mutations are autosomal recessive. When you cross flies that are both heterozygous for wrinkly mutations, you find that the F1 have a 6:1 ratio of normal:wrinkled wings. What is a likely explanation for this finding?

The wrinkly mutant allele is semi-lethal

FLies with the limpy mutation are uncoordinated. Some affected flies begin to show abnormal walking at 2 days old, whereas others take five or more days to show any problem. This is an example of:

variable expressivity

If a crossover occurs between two linked genes, what might be observed in the progeny?

recombinant combinations of the alleles of these two genes

If the genes a and b are 10cM apart, what fraction of the progeny will be recombinant?

10%

In a biosynthetic pathway A to B to C (letters are the names of molecules, C is the final product), the A to B step is catalyzed by Enzyme X, the B to C step is catalyzed by Enzyme Y. If X works at 50 molecules per minute and Y works at 10 molecules per minute, what will be the overall rate of production of C?

10 molecules per minute

Mutations of the gene FLO are dominant negative, and homozygous lethal. If someone who is homozygous for wildtype FLO alleles has children with someone who has the mutant FLO phenotype, what fraction of their children would you expect to have FLO disease?

50%

The stubby petal mutation in daffodils shows 60% penetrance. The mutation is autosomal recessive. If you cross two daffodils that are heterozygous for stubby petal mutations, what fraction of the F1 will show the stubby phenotype?

15%

Which of these is a missense non-conservative change?

Gly to Glu

Which statement is true about genes in which a null mutation is recessive?

It is haplosufficient

You have two different strains of cow, both of which have no tail. When you cross them, all of the F1 calves have a normal tail. What is a logical interpretation?

The mutations in the two strains are in different genes

In a GWAS to identify important risk loci for Thackeray Disease, what are you looking for?

SNPs that are found in people with the disease much more frequently than expected by chance

Thackeray Disease is due to mutations of a gene on Chromosome 7. The SNP called rs10556 is on chromosome 8, found in two forms, either G or A. In the general population 80% of alleles of rs10556 are G, the rest are A. What do you expect to see when you examine rs10556 among a large group of people with Thackeray Disease?

80% will have G, 20% will have A

In plasmid cloning, to join two DNA molecules from different sources together, which of these would make sense?

Cut them both with the same restriction enzyme first

What does Whole Exome Sequencing do?

Generate sequence of all the exons of all genes

What happens in the process referred to as transformation, during plasmid cloning?

The recombinant plasmid enters an E. coli cell

What is a "sticky end"?

The single-stranded overhang left after cutting DNA with a restriction enzyme

Which of these is NOT a useful aspect of Agrobacterium in making transgenic plants?

It generates a crown gall in the infected plant

Why is an antibiotic always used during plasmid cloning?

To kill the cells that have not taken up the plasmid

Why were some codons in the PSY and CRTI genes altered in making Golden Rice?

To remove rarely used codons that would have slowed translation

Why were the natural promoters for the PSY and CRTI genes not used in the completed recombinant Ti plasmid?

The genes needed to be transcribed specifically in one rice tissue

After the 4th cycle of PCR has been completed, there are found to be 100 molecules of the target present. How many molecules of the target would you expect to be present after four more cycles have completed?

1600

If NHEJ occurs after a chromosome break, what is likely to be the result?

the break is repaired, but usually with a mutation at the join that knocks out the gene

Take a look at the DNA sequence above, which of the sequences below could you order that could work to amplify the target by PCR, as the left-hand member of a pair?

5'-AGCTCGTATC-3'

To make a specific, desired mutation such as a missense change via CRISPR, why does there need to be a homology arm on each side of the repair template?

To provide a region for two crossovers, one each side of the change

What is happening during the 55-degrees celsius step of each PCR cycle?

Primers are binding to their complementary region of the DNA

What is the function of Cas9 in CRISPR?

To make a double-strand break in a chromosome

What is the function of each unique spacer within a natural crRNA made by wildtype bacteria?

to specify which viral genome the Cas9 enzyme cuts

Why are linkers added to the DNA used in Illumina sequencing?

To allow sequencing primers to bind to all fragments

To allow the DNA to bind to the flow-cell

To allow all the DNA fragments to be amplified on the flow-cell

Why can the original DNA strand be washed away after the first step in Illumina sequencing is complete?

A copy of it has already been made and is covalently bonded to the flow-cell

Why is a DNA polymerase specifically from Thermus aquaticus so critical to the process?

It is not denatured by the 95-degree celsius step in each cycle

A set of genes with a related function, transcribed in one mRNA from one promoter is a good description of what?

an operon

Copy Number Variants can be problematic because

there is an abnormal amount of wild-type protein for the genes in the CNV

How similar are the genomes of two randomly chosen people?

99\.9%

If a dominant mutation shows 65% penetrance, what fraction of individuals that are heterozygous will show the mutant phenotype?

65%

The idea that there are genetically distinct races is supported by genomic sequences from people across the world.

False

What two things do micro RNAs bind to, to achieve their function?

RISC and 3' UTR

What typically happens when an effector binds to an allosteric site?

The protein changes shape

Which of these can't be determined from RNA-seq data?

a. relative abundance of an mRNA compared to others

b. whether alternative splicing is occurring

c. whether a particular gene is expressed in a specific tissue

d. whether a candidate gene is actually a pseudogene

%%**e. all of the above can be determined**%%

Why do inversions often have no effect on phenotype?

the breaks that produce them don't disrupt any genes

You are annotating the newly sequenced genome of the great blue heron. The beta-globin gene in vertebrates usually has three exons and two introns. You find a long open-reading frame that would encode a standard globin protein, but it has no introns and there's a run of A's at the 3' end. This is probably what?

processed pseudogene

If a CpG island is heavily methylated, what will happen as a result?

the nearby gene will be turned off

If the level of cAMP in an E. coli cell is relatively low, what do you also definitely know about this cell?

the intracellular level of glucose is relatively high

If there is no lactose available, and the level of glucose in the cell is low, what will be the level of transcription seen in the lac operon?

very low, but not zero

What are the major components of nucleosomes?

Eight histones plus DNA wrapped around twice

What do HATs do?

add acetyl groups to histone, opening up the chromatin

What does the U2 snRNA bind to?

the branchpoint A of introns

What is the role of CAP in regulating the lac operon?

it adjusts transcription according to the exact level of glucose available

What is the role of SWI-SNF/BAP/BAF in eukaryotes?

to move nucleosomes around, adjusting chromatin compaction state

What of these is NOT an epigenetic change?

mutation of a base in the 5' UTR of a gene

Why do histones have so many lysine, arginine and histidines in them?

they are positively charged to counteract the negative charge of DNA

Dad is a 15//9 repeat genotype at a VNTR locus, Mom is a 4//10 genotype. which of these individuals is most likely to be their child?

Sinead, genotype 9//4

What happens within the D-loop of telomeres?

TTAGGG repeats bind to the CCCTAA-containing strand from earlier repeats

Which of these is NOT involved in the process of imprinting?

Ribosome mutations leading to altered translation level

Why are 5' methyl cytosines a hotspot for mutation?

they spontaneously lose an amino group, which causes mispairing

Why are VNTR loci important for DNA typing, and more individual specific than using SNPs?

there are many more alleles for each one, so people are usually heterozygous

Why do people with Fragile-X have the symptoms they do?

a repeat expands, generating a CpG island near the +1 site

Why do we lose about 150-200 nucleotides from each telomere each time the chromosome is replicated?

primase can't put a primer opposite the absolute end of the template

Why is dosage compensation needed?

males have only one X chromosome, whereas women have two

Why is Lysine 9 of histone H3 especially important?

it gets trimethylated as a key step in heterochromatin formation