Practice Exam for Test 4

How many nucleotides are in 12 mRNA codons?

36

In Charleston salamanders, eye color is inherited by one gene with four different alleles. Gametes from this salamander would have one of how many different possible alleles for the eye color gene?

4

Although the expression of most genes is tightly regulated, some genes are expressed at roughly constant rates (i.e., constitutively). Which of the following genes would you predict to be constitutively expressed?

genes that code for ribosomal RNAs

What amino acid would be added during translation if a point mutation in the codon for alanine changed the second base from C to G?

glycine

X-linked recessive traits in humans (or in Drosophila) are observed ________.

in more males than females

The reason for differences in the sets of proteins expressed in a nerve and a pancreatic cell of the same individual is that nerve and pancreatic cells contain different _____.

sets of regulatory proteins

What is an operon?

(sequence of functionally related genes under control of a single promoter)

Put the following events of elongation in prokaryotic translation in chronological order. 1. Binding of mRNA with small ribosomal subunit 2. Threading of mRNA along the small ribosomal subunit 3. Complementary base pairing between start codon and anticodon of the first tRNA 4. Base pairing of the mRNA codon following the start codon with its complementary tRNA 5. Attachment of the large subunit

1,2,3,5,4

A man has extra digits (six fingers on each hand and six toes on each foot). His wife and their daughter have a normal number of digits. Having extra digits is a dominant trait. The couple's second child has extra digits. What is the probability that their next (third) child will have extra digits?

1/2

A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). Albinism is an autosomal (not sex-linked) recessive trait. What is the probability that their first child will be an albino?

1/4

Suppose two AaBbCc individuals are mated. Assuming that the genes are not linked, what fraction of the offspring are expected to be homozygous recessive for the three traits?

1/64

When Mendel crossed yellow-seeded and green-seeded pea plants, all the offspring were yellow seeded. When he took these F1yellow-seeded plants and crossed them to green-seeded plants, what genotypic ratio is expected?

1:1

A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color blind marries a color-blind male. What is the probability that this couple's first son will be color blind?

50%

In tigers, a recessive allele causes a white tiger (absence of fur pigmentation). If one phenotypically normal tiger that is heterozygous is mated to another that is phenotypically white, what percentage of their offspring is expected to be white?

50%

How many potential Open Reading Frames (ORFs) are there from double stranded DNA?

6

In humans, ABO blood types refer to glyocproteins in the membranes of red blood cells. There are three alleles for this autosomal gene: IA, IB, and i. The IA allele codes for the A glycoprotein, The IB allele codes for the B glycoprotein, and the i allele codes for the O glycoprotein. IA and IB are codominant, and i is recessive to both IA and IB. People with A type blood have the genotypes IAIA or IAi, people with type B blood are IBIB or IBi, people with type AB blood are IAIB, and people with O type blood are ii. If a woman with type AB blood marries a man with type O blood, which of the following blood types could their children possibly have?

A and B

If the DNA code for a particular amino acid is AGT, then the anticodon on the tRNA would be _____.

AGU

Which one of the following, if missing, would prevent translation from starting?

AUG codon

A black guinea pig crossed with an albino guinea pig produced 12 black offspring. When the albino was crossed with a second black animal, 6 blacks and 6 albinos were obtained. What is the best explanation for this genetic situation?

Albino is recessive; black is dominant.

There are 61 codons that each specify the addition of a specific amino acid, and three stop codons for which there is no corresponding amino acid. However, there are only about 40 tRNA molecules, representing 40 anticodons. How is that possible?

An anticodon forms hydrogen bonds with the codon; it must match the first two bases of the codon, but is less specific with respect to the third base.

B = big peppers; b = small peppers; R = red peppers; r = yellow peppers. You have one bush that produces big yellow peppers and another bush that produces small red peppers. When the two are crossed, you find that half of the new bushes produce big red peppers and half produce small red peppers. What are the genotypes of the parents? SHOW YOUR WORK.

Bbrr, bbRR bbRR, Bbrr

Genotype is to _____ as phenotype is to _____.

DNA base sequence; amino acid sequence

Which is the correct order for one cycle of polymerase chain reaction (PCR)?

Denature DNA; anneal primers; extend DNA from primers.

As scientists were unraveling the mysteries associated with transcription and translation, they discovered there was not a one-to-one correspondence between nucleotide sequence of a gene and base sequence of the mRNA it codes for. They proposed the genes-in-pieces hypothesis. How can the genes-in-pieces hypothesis be explained?

Introns are noncoding segments of DNA that are present in the initial transcript, but are removed by splicing.

How might a single base substitution in the sequence of a gene affect the amino acid sequence of a protein encoded by the gene, and why?

Only a single amino acid could change, because the reading frame is unaffected.

Sequencing an individual person's genome

could lead to legal issues regarding discrimination and privacy, could help make informed choices about medical treatment., and currently possible

In early forensic applications of DNA fingerprinting, DNA was extracted from crime scene material, digested with restriction enzymes, and then used to prepare a Southern blot. Today, polymerase chain reaction (PCR) is used in the early steps of forensic DNA analysis. Which of the following is an advantage that PCR provides over the former method?

PCR requires much less DNA for analysis

In negative control of transcription, a gene is activated when _____.

a regulatory protein is removed from DNA

How does termination of translation take place?

a stop codon is reached

Not long ago, it was believed that a count of the number of protein-coding genes would provide a count of the number of proteins produced in any given eukaryotic species. This is incorrect, largely due to the discovery of widespread _____.

alternative splicing

During translation, polypeptides are assembled from _____.

amino acids

Which end of the amino acid is attached to the 3' end of the transfer RNA?

carboxyl

What happens when DNA is heated to 95 degrees C during the polymerase chain reaction?

double strand separates when hydrogen bonds break between base pairs

Name a region of eukaryotic DNA that would bind a regulatory transcription factor.

enhancer, silencer, promoter proximal element

The primary difference between an enhancer and a promoter-proximal element is that _____.

enhancers are at considerable distances from the promoter and can be moved or inverted and still function; promoter-proximal elements are close to the promoter and their position and orientation must be maintained

During alternative splicing of messenger RNA, what can be removed along with the introns?

exons

Which of the following is not one of the steps in initiation of translation?

formation of a polypeptide bond

Snapdragons are flowers that come in a variety of colors, including red, pink, and white. A series of crosses with snapdragons having flowers of different colors produced the following results: pink × pink: 27 pink, 13 red, 14 white red × red: all red white × white: all white pink × white: 29 pink, 26 white pink × red: 28 pink, 27 red white × red: all pink

incomplete dominance

The lac repressor blocks transcription of the lac operon when the repressor _____.

is not bound to lactose

Does DNA have a positive or negative charge?

negative

Histone acetyl transferases exert their effect on gene activity by _____.

neutralizing positive charges on the lysines of histones

The RNA components of ribosomes are synthesized in the ________.

nucleolus

In the lac operon, what DNA sequence does the repressor protein bind to? It is between the promoter and the coding region.

operator

The observable traits expressed by an organism are described as its ________.

phenotype

If a biologist wanted to analyze the evolutionary relationship in a gene type that is found in both eukaryotes and bacteria, which of the following would NOT be useful?

prevent progression of the cell cycle unless conditions are right for moving forward

The normal function of a tumor suppressor gene is to _____.

prevent progression of the cell cycle unless conditions are right for moving forward

Mendel crossed yellow-seeded and green-seeded pea plants and then allowed the offspring to self-pollinate to produce an F2generation. The results were as follows: 6022 yellow and 2001 green (8023 total). The allele for green seeds has what relationship to the allele for yellow seeds?

recessive

Pseudohypertrophic muscular dystrophy is a human disorder that causes gradual deterioration of the muscles. Only boys are affected, and they are always born to phenotypically normal parents. Due to the severity of the disease, the boys die in their teens. Is this disorder likely to be caused by a dominant or recessive allele? Is its inheritance sex-linked or autosomal?

recessive, sex linked

Once a peptide has been formed between the amino acid attached to the tRNA in the P site and the amino acid associated with the tRNA in the A site, which process on the list occurs next?

translocation to open the A site for the next tRNA