Exam #7

Question 1

When Thomas Hunt Morgan crossed his red- eyes F1 generation files to each other, the F2 generation included both red- and white- eyed files. Remarkably, all the white eyed files were male. What was the explanation for this result?

• The gene involved is on an autosome, but only in males
• The gene involved is on the Y chromosome.
• The gene involved is on the X chromosome.

Answer 1

The gene involved is on the X chromosome.

Question 2

Which of the following is the meaning of the chromosome theory of inheritance as expressed in the 20th century?

• Mandelian genes are at specific loci on the chromosomes and in turn segregate dur
• No more than a single pair of chromosomes can be found in a healthy normal cell
• Individuals inherit particular chromosomes attached to genes

Answer 2

Mendelian genes are at specific loci on the chromosomes and in turn segregate dur

Question 3

Males are more often affected bye sex- linked traits then females because

• males are hemizygous for the X chromosomes
• mutations on the Y chromosomes often worsen the effects of X-linked mutations
• male hormones such as testerone often alter the affects of mutations of the X chromosome

Answer 3

Males are hemizygous for the X chromosome

Question 4

SRY is the best described in which of the following ways?

• a gene region present on the Y chromosome that triggers male development
• a gene present on the X chromosomes that triggers female development
• an autosomal gene that is required for the expression of genes on the X chromosomes

Answer 4

A gene region present on the Y chromosome that triggers male development

Question 5

Normally, only female cats have the tortoiseshell phenotype because

• the Y chromosome that has a gene blocking orange coloration
• the males die during embryonic development
• a male inherits only one allele of the X - linked gene controlling hair color.

Answer 5

A male inherits only one allele of the X- linked gene controlling hair color.

Question 6

Sex determined in mammals is due to the SRY region of the Y chromosome. An abnormality of this region could allow which of the following to have a male phenotype ?

• Down syndrome, 46, XX
• translocation of SRY to an autosome of a 46, XX individual
• a person with an extra X chromosomes

Answer 6

Translocation of SRY to an auto some of a 46, XX individual

Question 7

In humans, clear gender differentiation occurs not at fertilization, but after the second month of gestation. What is the first event of this differentiation ?

• activation of SRY in females and feminization of the gonads
• activation of SRY in male embryos and masculinization of the gonads
• formation of estrogens in female embryos

Answer 7

Activation of SRY in male embryos and masculinization of the gonads

Question 8

Duchesse muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome. The patients have muscles that weaken over time becuase they have absent or decreased dystrophin, a muscle protein. They rarely live past their 20s. How likely is it for a woman to have this condition?

• Vary rarely
• Woman can never have this condition
• One- half of the daughters are affected

Answer 8

Very rarely : it is rare that an affected male would mate with a carrier female.

Question 9

All female mammals have on active X chromosome per cell instead of two. What causes this?

• attachment of methyl ( CH3) groups to the X chromosomes that will remain active
• activation of the XIST gene on the X chromosome that will become the Barr body
• activation of the BARR gene on one X chromosomes, which then becomes inactive

Answer 9

Activation of the XIST gene on the C chromosome that will become the Barr body

Question 10

What does a frequency of recombination of 50% indicate?

• Independent assortment is hindered.
• The two genes are likely to be located on different chromosomes
• The genes are located on sex chromosomes

Answer 10

The two genes are likely to be located on different chromosomes.

Question 11

What is one map unit equivalent to ?

• 1% frequency of recombination between two genes
• the distance between a pair of homologs chromosomes
• the physical distance between two linked genes

Answer 11

1% frequency of recombination between two genes

Question 12

What is the reason that closely linked genes are typically inherited together?

• The likelihood of a crossover event between these two genes is low.
• Genes align that way during metaphase I of meiosis
• Chromosomes are un breakable

Answer 12

The likelihood of a crossover enemy between these two genes is low.

Question 13

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?

• There are four major functional classes of genes in Drosophila
• The overall number of genes in Drosophilia is a multiple of four
• Drosophila genes cluster into four distinct groups of linked genes.

Answer 13

Drosophila genes cluster into four distinct groups of linked genes.

Question 14

One possible result of chromosomal breakage for a fragment to join a nonhomolgous chromosome. What is this alteration called?

• inversion
• translocation
• deletion

Answer 14

Translocation

Question 15

A no reciprocal crossover causes which of the following products?

• deletion and duplication
• duplication only
• deletion only

Answer 15

Deletion and duplication

Question 16

How do we describe transformation in bacteria ?

• assimilation of external DNA into a cell
• the creation of a strand of DNA from an RNA molecule
• the infection of cells by a phage DNA molecule

Answer 16

Assimilation of external DNA into a cell

Question 17

After mixing a heat - killed, phosphorescent ( light - emitting ) strain of bacteria with a living, nonphosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observations would provide the best evidence that the ability to phosphorescence is a heritable trait?

• The phosphorescence in the living strain is especially bright.
• Descendants of the living cells are also phosphorescent
• DNA passed from the heat- killed strain to the living strain

Answer 17

Descendants of the living cells are also phosphorescent.

Question 18

In trying to determine wheher DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?

• DNA contains nitrogen, whereas protein does not
• DNA contains phosphorus, whereas protein does not
• DNA contains Sulfur, whereas protein does not

Answer 18

DNA contains phosphorus, whereas protein does not .

Question 19

Which of the following investigation was responsible for the following discovery? In DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine.

• Erwin Chargaff
• Alfred Hershey and Martha Chase
• Matthew Meselson and Franklin Stahl

Answer 19

Erwin Chargaff

Question 20

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

• 42%
• 8%
• 16%

Answer 20

8%

Question 21

Which of the following can be determine directly from X - Ray photographs of crystallized DNA?

• the sequence of nucleotides
• the rate of replication
• the diameter of the helix

Answer 21

The diameter of the helix

Question 22

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary info in which of the following?

• sequence of bases
• side groups of nitrogenous bases
• different five- carbon sugars

Answer 22

Sequence of bases

Question 23

An Okazaki fragment has which of the following arrangement?

• 5’ DNA to 3’
• 5’ RNA nucleotide, DNA nucleotide 3’
• Primase, polymerase, ligase

Answer 23

5’ RNA nucleotides, DNA nucleotides 3’

Question 24

Which enzyme catalysts the elongation of a DNA strand in the 5’ -> 3’ direction ?

• DNA polymerase III
• Primase
• DNA ligase

Answer 24

DNA polymerase III

Question 25

What is the function of topoisomerase?

• relieving strain in the DNA ahead of the replication fork
• adding methyl groups to bases of DNA
• unwinding of the double helix

Answer 25

Relieving strain in the DNA ahead of the replication fork

Question 26

What is the role of DNA ligament in the elongation of the lagging strand during DNA replication?

• It stabilizes the unwound parental DNA
• It synthesizes RNA nucleotides to make a primer
• It joins Okazaki fragments together

Answer 26

It joins Okazaki fragments together.

Question 27

Which of the following helps to hold the DNA strands apart while they are being replicated?

• Single strand binding proteins
• ligase
• Primase

Answer 27

Single - strand binding proteins

Question 28

Individuals with the disorder xeroderma pigmentosum are hypersensitive to the sunlight. This occurs because their cells are impaired in what way?

• They cannot replicate DNA
• The cannot undergo mitosis
• They cannot repair thymine dimers

Answer 28

They cannot repair thymine dimers.

Question 29

Which of the following sets of materials is required by both eukaryotes and prokaryotes for replication?

• ligase, primers, nucleases
• double- stranded DNA, four kinds of dNTPs, primers, origins of replication
• topoisomerase, telomerases, polymerases

Answer 29

Double - stranded DNA, four kinds of dNTPs, primers, origins of replication.

Question 30

Which of the following statements describes the eukaryotic chromosome?

• It consists of a single linear molecule of double- stranded DNA plus proteins
• it composed of DNA alone
• The nucleoside is its most basic functional subunit

Answer 30

It consists of a single linear molecule of double- stranded DNA plus protein.