Genetics Test 2 Mastering
Suppose a diploid cell with three pairs of homologous chromosomes (2n = 6) enters meiosis. How many chromosomes will the resulting gametes have if nondisjunction of all three chromosome pairs in meiosis I
0 or 6. If all chromosome pairs undergo nondisjunction in meiosis I, half the gametes will have twice the normal haploid number of chromosomes (2n), and half will have no chromosomes.
Suppose a diploid cell with three pairs of homologous chromosomes (2n = 6) enters meiosis. How many chromosomes will the resulting gametes have if nondisjunction of all three chromosomes in one daughter cell in meiosis II
0,3, or 6. If all chromosomes undergo nondisjunction in meiosis II, half the gametes will have the normal haploid number of chromosomes (n), one-quarter will have twice the haploid number (2n), and one-quarter will have no chromosomes.
deoxyribose sugar links
1' carbon links to base, 2' and 4 carbon no linkage, 3' and 5' carbon links to next nucleotide
Suppose a diploid cell with three pairs of homologous chromosomes (2n = 6) enters meiosis. How many chromosomes will the resulting gametes have if nondisjunction of one chromosme pair in meiosis I
2 or 4. If one chromosome pair undergoes nondisjunction in meiosis I, half the gametes will have an extra chromosome (n +1), and half will be missing a chromosome (n - 1).
Suppose a diploid cell with three pairs of homologous chromosomes (2n = 6) enters meiosis. How many chromosomes will the resulting gametes have if nondisjunction of one chromosome in one daughter cell in meiosis II.
2,3,or 4. If one chromosome undergoes nondisjunction in meiosis II, half the gametes will have the normal haploid number of chromosomes (n), one-quarter will have an extra chromosome (n +1), and one-quarter will be missing a chromosome (n - 1).
Suppose a diploid cell with three pairs of homologous chromosomes (2n = 6) enters meiosis. How many chromosomes will the resulting gametes have if meiosis occurs normally?
3
If 15% of the nitrogenous bases in a sample of DNA from a particular organism is thymine, what percentage should be cytosine?
35%
The condition known as cri-du-chat syndrome in humans has a genetic constitution designated as...?
46, 5p-
What is the complementary DNA sequence to 5′ ATGCTTGACTG 3′
5′ CAGTCAAGCAT 3′
For a species with a diploid number of 12, indicate how many chromosomes will be present in the somatic nuclei of individuals that are haploid, triploid, tetraploid, trisomic, and monosomic.
6;18; 24; 13; 11
One of the most common spontaneous lesions that occurs in DNA under physiological conditions is the hydrolysis of the amino group of cytosine, converting the cytosine to uracil. What would be the effect on DNA structure of a uracil group replacing cytosine?
A base substitution of G:C to A:T after two rounds of replication.
Which of the following arrangements would yield the greatest reduction in gamete viability? An inversion homozygote for a large inversion; An inversion heterozygote for a large inversion; An inversion homozygote for a small inversion; An inversion heterozygote for a small inversion
An inversion heterozygote for a large inversion. A large heterozygous inversion will result in greater numbers of genes that are duplicated or deleted when crossing over occurs.
Predict the genetic composition of gametes derived from tetrads of inversion heterozygotes where crossing over occurs within a pericentric inversion.
Crossing over in the inversion loop of a pericentric heterozygote produces all chromatids with centromeres, but the two chromatids involved in the crossover are genetically unbalanced. The balanced chromatids are of either normal or inverted sequence.
Why does crossing over occur more often between two distantly linked genes than between two closely linked genes on the same chromosome?
Crossing over is somewhat randomly distributed over the length of the chromosome. Two loci that are far apart are more likely to have a crossover between them than two loci that are close together.
central conclusion of the Hershey-Chase experiments?
DNA is the identity of the hereditary material in phage T2.
methods for determining the linkage group and genetic map in humans involve
DNA markers
Which of these three human chromosomal abnormalities--Down, Patau, or Edwards syndrome--has the longest average survival time? Why is that the case?
Down syndrome, because trisomy 21 involves the smallest chromosome of the three.
which technique can be used to identify the location of genes on a chromosome?
FISH. Fluorescent in situ hybridization is a technique used to identify the location of a gene or a specific DNA sequence on a chromosome. The technique involves hybridizing single-stranded DNA probes, labeled with a fluorescent dye, to their complementary DNA strand in the genome. Their location on the chromosome can be viewed under a fluorescent microscope.
T/F. Of the three types of segregation possible at anaphase I in translocation heterozygotes, all occur with roughly equal frequency.
False. Correct. Adjacent-2 segregation is far less common than either adjacent-1 or alternate segregation patterns.
T/F. Females with only one X chromosome do not develop; this condition is lethal.
False. Females with only one X chromosome are viable but have Turner syndrome, which is characterized by underdeveloped ovaries. Males that lack an X chromosome do not develop; this condition is lethal.
T/F. Inversion loops do NOT form during meiosis in paracentric inversion heterozygotes
False. Loop formation allows pairing within inverted regions of homologous chromosomes regardless of whether the centromere is included in the inversion.
T/F. In order to create the possibility of generating a trisomy, nondisjunction must occur during meiosis II.
False. Nondisjunction during either meiosisI or meiosis II creates gametes that will generate trisomies if fertilized.
Which of the following syndromes is not paired with its causative chromosomal aberration? Cri du chat syndrome - deletion; Huntington disease - duplication; Fragile X syndrome - deletion; Down syndrome - Robertsonian translocation
Fragile X syndrome-deletion. Fragile X syndrome is an example of a trinucleotide repeat disorder, which shows increasing severity with increased copy number of a specific three‑base sequence.
Familial Down syndrome facts
It accounts for approximately 5% of all Down syndrome cases. Heterozygous carriers of the Robertsonian translocation that causes familial Down syndrome can have children who are phenotypically normal and are not carriers of the translocation. Heterozygous carriers of the Robertsonian translocation that cause familial Down syndrome can have children who are also carriers of the translocation. Three viable zygote types are possible when fertilization occurs between one normal and one heterozygous parent. One-third has a normal chromosome complement, one-third is a carrier, and one-third has Down syndrome.
The Hershey and Chase experiments involved the preparation of two different types of radioactively labeled phage. Why were two preparations were required?
It was necessary that each of the two phage components, DNA and protein, be identifiable upon recovery at the end of the experiment.
Inversions are said to "suppress crossing over." Is this technically correct? Why or why not
No, crossovers still occur, but deleted or duplicated sequences in the resulting chromosomes reduce viability of potential zygotes.
What phenotype would be expected in balanced translocation heterozygotes in the absence of position effects?
Normal, Because they have a normal amount of genetic material. Balanced translocation heterozygotes have a normal amount of genetic material, but it is in a translocated configuration. As long as there are no position effects, these individuals can be phenotypically normal
In the classic experiment conducted by Hershey and Chase, why was the pellet radioactive in the centrifuge tube that contained bacteria with viruses?
The bacteria were in the pellet, and many contained the radioactive viral DNA
What essential criteria must be met in order to execute a successful mapping cross?
The genotypes of the offspring must be readily determined from their phenotypes. Recombination must occur in the sex that displays genetic heterogeneity. One parent should be heterozygous and the other homozygous recessive for all the genes being mapped.
What observation did Griffith make in his experiments with Streptococcus pneumoniae?
The mouse did not survive when injected with a mixture of live, avirulent (rough) Streptococcus pneumoniae and heat-killed, virulent Streptococcus pneumoniae.
DNA structure
The nucleic acid strands in a DNA molecule are oriented antiparallel to each other, meaning they run in opposite directions.
Predict how the synaptic configurations of homologous pairs of chromosomes might appear when one member is normal and the other member has sustained a deletion or duplication.
There will be point-for-point pairing in all sections that are capable of pairing. The section that has no homolog will loop out to form a deletion or compensation loop
T/F. Gene duplications provide an explanation for the origin of gene families.
True
T/F. Duplications and deletions can be detected during meiosis by the presence of extrachromosomal loops that do not pair properly with their homolog.
True. During meiosis, the presence of a chromosomal loop signals that a duplication or deletion has occurred.
trisomy
a gain of one chromosome in addition to an otherwise diploid genome
aneuploidy
a general condition when an organism gains or loses one or more chromosomes but not a complete set
monosomy
a loss of one chromosome from an otherwise diploid genome
what is the proposed basis for positive interference
a physical rigidity of chromatids
autotetraploid
a polyploid that has two extra sets of chromosomes, identical to the normal haploid complement of the same species.
patau syndrome
a trisomy of chromosome 13 in humans
edwards syndrome
a trisomy of chromosome 18 in humans
transfer RNA
acts as the link btw codons and amino acids; has a cloverleaf secondary structure
Recombination frequencies between linked genes along a chromosome are
additive, so the recombination frequency between genes X and Z is 25 + 5 = 30.
amphidiploid
an allotetraploid derived from two known original species
paracentric inversion
an inversion that has breakpoints that do not include the centromere
pericentric inversion
an inversion that has breakpoints that include the centromere
What is the chemical basis of molecular hybridization?
base complementarity
The basic structure of a nucleotide includes
base, sugar, and phosphate
why does RNA act differently than DNA during electophoresis
because of intrastrand base pairing of single stranded RNA molecules
messenger RNA
carries information from the nucleus to cytoplasm; sequence specifies the order of amino acids in a protein
ribosomal RNA
catalyzes the formation of peptide bonds btw amino acids; a structural part of the enzyme responsible for translation
All of the following could result from meiosis in a pericentric inversion heterozygote in which a single crossover occurred within the inversion loop except a _______. chromosome with some duplicated regions; completely normal chromosome; chromosome with two centromeres; chromosome with some deleted regions
chromosome with two centromeres. When the centromere is contained within the inversion, it is neither duplicated nor deleted
How many chromosomes would be found in an allopolyploid plant if its parents had diploid numbers of 4 and 6 respectively?
diploid number of 5. The parents contribute 2 and 3 chromosomes respectively to each of their gametes.
clusters of terms accurately describes DNA as it is generally viewed to exist in prokaryotes and eukaryotes
double-stranded, antiparallel, (A + T)/C + G) = variable, (A + G)/(C+ T) = 1.0
Each of the following is a consequence of heterozygous reciprocal translocation except... semi-sterility; production of completely normal gametes; failure of homologous chromosome pairing; production of gametes that contain both duplications and deletions
failure of homologous chromosome pairing. Homologous regions of chromosomes in translocation heterozygotes are able to pair with one another.
T/F. Hershey and Chase used labeled DNA and protein to determine that DNA is the genetic material in bacteria
false
T/ F. Crossing over during prophase I of meiosis occurs between alleles on sister chromatids
false. Crossing over during meiosis occurs between alleles on nonsister chromatids.
A cross between a tetraploid and a diploid member of the same species will produce offspring that can undergo sexual reproduction.
false. Offspring from this cross would be triploid and produce gametes with an uneven number of homologous chromosomes, making sexual reproduction unlikely.
euploidy
general condition where complete haploid sets of chromosomes are present
In 1928, Frederick Griffith established that
heat-killed bacteria harbor the constituent(s) necessary to convey genetic properties to living bacteria. Because some of the nonvirulent bacteria acquired properties of the virulent bacteria, instructions for this transformation must be carried by the virulent bacteria.
Which of the following accurately describes a possible meiotic nondisjunction event? Meiosis fails to proceed to completion. Homologs fail to separate during meiosis I. Fusion of gametes results in trisomy. Sister chromatids fail to separate during meiosis I.
homologs fail to separate during meiosis 1
Considering the structure of double-stranded DNA, which kind(s) of bonds hold one complementary strand to the other?
hydrogen
To be certain that the extract prepared from virulent cells still contained the transforming principle that was present prior to lysis, Avery _______.
incubated nonvirulent cells with the complete extract. The complete extract possessed the same ability to induce transformation in IIR bacteria as whole heat-killed IIS bacteria.
the genetic material must be stable enough to maintain...
information in storage from one cell to the next and one organism to the next
deletion
loss of part of a chromosomal segment
allopolyploid individuals
may be sterile and unable to produce offspring
linkage of purine and pyrimidine
n purines, the N-9 atom is covalently bonded to the C-1' of the sugar. In pyrimidines, the N-1 atom is covalently bonded to the C-1' of the sugar.
The incidence of Down syndrome, also known as trisomy 21, increases with increasing maternal age. What error most likely produces this condition?
nondisjunction during either meiosis I or II in the female gamete. Nondisjunction during either meiosis I or II can produce a gamete that will result in a trisomic zygote. Since the incidence of Down syndrome increases with maternal age, it is likely that this error occurs in the female gamete.
Regarding the structure of DNA, the covalently arranged combination of a deoxyribose and a nitrogenous base would be called a(n)
nucleoside
Events that occur during normal meiosis
one diploid cell produces four haploid cells, sister chromatids separate from one another during meiosis II, homosolous chromosomes separate from one another during meiosis I.
The classic Hershey and Chase (1952) experiment that offered evidence in support of DNA being the genetic material in bacteriophages made use of which of the following labeled component(s)?
phosphorus and sulfur
If Avery had observed transformation using only the extracts containing degraded DNA, degraded RNA, and degraded protein, but NOT the extract containing degraded polysaccharides, he would have concluded that _______.
polysaccharides are the genetic material. Failure to transform suggests that the chemical degraded in that preparation is the one responsible for transformation, in this case polysaccharides.
the phenomenon in which one crossover decreases the likelihood of crossovers in nearby regions is called
positive interference
Guanine and adenine are...
purines found inDNA
hydrogen bonds
responsible for base complementarity; electrostatic charge attraction; weak bonds (easy to break)
structure difference of ribose and deoxyribose
ribose has the OH group of the 2' carbon. Deoxyribose just has H group.
Watson and Crick used information from several individuals to construct their model of DNA. Whose X-ray diffraction studies were critical to their work
rosalind franklin
covalent bonds
sharing of electrons btw two or more atoms; strong bonds (difficult to break)
What is the physical state of DNA after being denatured by heat?
single-stranded
autopolyploidy
the addition of one or more extra sets of chromosomes, identical to the normal haploid complement of the same species.
allopolyploidy
the case of polyploidy when the chromosomes originate from the hybridization of two different species, usually closely related.
the more hydrogen bonds btw bases,...
the higher the temp needed to separate the pair
replication
the process that leads to the production of identical copies of the existing genetic information.
expression
the processing of genetic information that results in synthesis of proteins which contribute to the phenotype of the organism
The probability of a double crossover is
the product of the probabilities of the single crossovers: 0.25 x 0.05 = 0.0125, or 1.25%.
thymine and cytosine are
the pyrimidines found in DNA
mutation
the random variation of genetic material that provides the basis for evolution
inversion
the removal of a segment followed by its reinsertion into the same chromosome in the reverse orientation.
duplication
the repetition of a segment. The repeated segment may be located next to the original or at a different location, and its orientation may be the same as the original or the reverse.
For a given meiosis in a translocation heterozygote, the factor that determines whether the resulting gametes are genetically complete is _______.
the segregation pattern of chromosomes at anaphase I. Alternate segregation at anaphase I will result in the formation of genetically complete gametes.
Describe the cytological observation that suggests that crossing over occurs during the first meiotic prophase.
the side-by-side pairing of chromosomes; chiasmata
A Robertsonian translocation is considered non-reciprocal because _______.
the smaller of the two reciprocal products of translocated chromosomes is lost. After several cell divisions, only the larger of the two translocated chromosomes remains. Its reciprocal is lost.
translocation
the transfer of a segment to a nonhomologous chromosome. Translocations may be reciprocal (two nonhomologous chromosomes exchange segments) or nonreciprocal (one chromosome transfers a segment without receiving one).
individual organisms with 27 chromosomes are _____ and are more likely to be sterile because there are ______at meiosis I that cause a relatively high number of unbalanced gametes to be formed.
triploid (3n); trivalents
G-C base pairs have three hydrogen bonds while A-T base pairs have
two hydrogen bonds
nondisjunction products during meiosis I
two products of the second meiotic division have both the maternal and paternal chromosmes of a set and the other two products have none for that set.
A genomic condition that may be responsible for some forms of fragile-X syndrome, as well as Huntington disease, involves ________.
various lengths of trinucleotide repeats.
if interference is complete, what is the frequency of double crossovers
zero
