Genetics Chapter 6
To conduct a chi square analysis to discriminate between linkage and independent assortment in a cross, a scientist needs
-The expected number of recombinant offspring. -The expected number of non recombinant offspring. -A hypothesis.
You perform a particular three-point test cross in Drosophila that produced 1,000 flies. You expect 30 double crossover recombinants, however, you could only detect 24. What is the value for interference?
0.20
In a small animal, P, E and B are found on a chromosome at map positions 5, 25, and 55, respectively. A three-factor cross was performed that yielded 1,000 progeny, including 42 double crossover recombinants. What is the value for interference?
0.30
Refer to the data of question 17. What is the value for interference?
0.64
What is the value for interference if the coefficient of coincidence is 0.3?
0.7
Genes a, b and c are linked on a particular chromosome in this order. The distance between a and b is 9.0 map units, while b and c are 30 map units apart. What is the probability of a double crossover if interference in this chromosomal region is 70%?
0.81%
Genes x, y and z are linked on a particular chromosome in this order. The distance between x and y is 7.5 map units, while y and z are 23.1 map units apart. What is the probability of a double crossover in this chromosomal region? (Assume no interference)
1.73%
In dragons, straight tails require the presence of either or both of two dominant alleles, Z and T. Individuals homozygous for both recessive alleles have zigzag tails. The two genes are on the same chromosome and recombine with a frequency of 24 percent. From the cross ZT/zt X ZT/zt, what is the expected frequency of individuals with zigzag tail in the progeny?
14.44%
How many phenotypic classes are expected in the progeny of a FOUR-POINT test cross?
16
Genes A and B are linked with recombination frequency of 0.2. Both genes segregate dominant (A and B) and recessive alleles (a and b). The parental cross AABB x aabb is performed and then the F1 progeny is testcrossed to aabb. If 10 individuals are counted in the F2, how many are expected to have recombinant phenotypes?
2
In a particular plant, genes A and B are completely linked. A plant of genotype A b/A b is crossed with one of genotype a b/a b. Which of the following is TRUE?
All progeny will be phenotypically Ab
Alternative names for genetic mapping
Chromosome mapping Gene mapping
Assume that a cross is made between AaBb and aabb plants, and all of the offspring are either AaBb or aabb. These results are consistent with which of the following circumstances?
Complete linkage
Geneticists only study the transmission of one character at a time in a given genetic cross.
FALSE
What is the name of the phenomenon in which genes located together on a chromosome are usually transmitted together?
Genetic linkage
Recombination frequencies
increase with genetic distance.
The number of _____ offspring divided by the total number of offspring multiplied by 100 equals the genetic _____ distance.
recombinant; map
The fraction of ____ in a testers gives an idea of the physical ____ between two genes on the same chromosome.
recombination; distance
Results from the experiments by McClintock and Creighton supported the view that genetic _____ involves a physical exchange between _____ chromosomes.
recombination; homologous
In a particular animal, genes C and D are unlinked. A plant of genotype C/C D/D is crossed with one of genotype c/c d/d. The F1 animals are then testcrossed. What percent of the F2 generation is expected to be c/c d/d?
25%
Refer to the data of question 17. The map distance between the genes A/a and C/c is
27
Refer to the data of question 17. The map distance between the genes B/b and C/c is
31
Refer to the organism of question 22. From the cross Zt/zT X ZT/zt, what is the expected frequency of individuals with zigzag tails in the progeny?
4.56%
How many map units apart do two genes have to be to follow the law of independent assortment?
50 mu
The corn chromosome 9 used in experiments by Creighton and McClintock had what unusual structural features?
A knob at one end of the chromosome, and a translocation of piece of chromosome 8.
Which of the following statements best defines a linkage group?
All of the genes that are located on the same chromosome.
Which of the following statements about crossing-over is TRUE?
It does not occur in Drosophila melanogaster males.
How many genes does a typical human chromosome contain?
Many hundreds
Consider three genes P, Q and R, that have the following distances in map units: P-Q = 3 m.u; P-R = 7 m.u; and Q-R = 10 m.u. What is the gene order?
Q-P-R
Crossing over does not occur during _____ formation in Drosophila.
Sperm
Alternative methods of gene mapping allow genes to be mapped in species with long generation times or without experimental crosses.
TRUE
What explanation did Bateson and Punnett offer for their results in which the observed numbers from a two-factor cross did not conform to a 9:3:3:1 ratio?
The transmission of the two characters from the parental generation to the F2 generation was coupled and not assorted independently.
A positive value for interference suggests
a crossover in one region of a chromosome decreases the probability that a second crossover will occur nearby.
A testcross is a cross between
a heterozygote and a recessive homozygote.
A triple heterozygote (AaBbCc) was mated to a triple recessive (aabbcc). The progeny were as follows: ABC 4 aBC 335 aBc 48 ABc 127 abC 123 AbC 51 Abc 327 abc 5 The allele arrangement in the triple heterozygote must have been
aBC/Abc
Crossovers produce recombinant chromosomes through
an exchange of chromosomal segments between homologous chromosomes.
The terms cis and trans describe the
arrangement of alleles on homologous chromosomes.
The first direct evidence that genes are physically located on the same _____ came from the studies of _____, who studied the inheritance pattern of characters following an _____- linked pattern of inheritance.
chromosome; Thomas Hunt Morgan; X
A _____ is sometimes called a _____ _____ because it contains a group of genes that are physically linked together.
chromosome; linkage group
In Drosophila, the genes j and r are linked. Parental flies of genotype j+ r+/ j+ r+ and j r/ j r are crossed. What allele arrangement would the F1 flies contain?
cis
Genetic mapping is based on estimating the distance between linked genes based on the likelihood that a _____ will occur between them.
crossover
Morgan proposed that the likelihood of crossing over depends on the _____ between two genes.
distance
In a three-factor cross, ____ crossovers are incorporated into map distance by multiplying their number by 2 and adding this number to the previous value of _____ offspring in the equation for map distance.
double; recombinant
McClintock and Creighton hypothesized that a crossover between a normal chromosome 9 and a knobbed/translocated chromosome 9 would produce a recombinant chromosome that had
either a knob and a translocation, but not both.
A gene distance of 1 cM is
equivalent to 1% recombination and 1 map unit.
A diploid cell has a pair of homologous chromosomes. One chromosome has the alleles FGH and the other chromosome has the alleles ugh. The cell undergoes meiosis. Which alleles would be found in the non recombinant haploid cells.
fgh; FGH
A double crossover between two genes could involve _____, _____, or _____ chromatids.
four, three, or two
Traditional genetic mapping approaches are feasible in
fungi; Drosophila; algae; several plant species
A known locus of a _____ within a genetic _____ may help molecular geneticists to clone the _____.
gene; map; gene
The transmission of _____ that are close to each other on the same chromosome violates the law of _____ _____.
genes; independent assortment
A _____ _____ is a diagram that describes the order of genes along a chromosome.
genetic map
Statistical analysis cannot prove that a _____ is true.
hypothesis
Linkage violates which of the following Mendelian principles?
independent assortment
A _____ and a _____ on corn chromosome 9 proved instrumental in showing that crossing over can result in genetic recombination, in experiments by Creighton and McClintock.
knob; translocation
You may have noticed that people who have red hair usually have freckles too. Which of the following can best describe this phenomenon?
linkage
When conducting a chi square analysis to determine if genes in a two factor cross are linked or independently assorted, scientists begin with the hypothesis that the genes are not _____.
linked
Distance on a chromosome is generally measured in
map units (mu), and centiMorgans (cM)
When two genes are linked, offspring tend to inherit the _____ pattern of alleles more often than the _____ pattern of alleles.
non-recombinant; recombinant
Genes C and D are linked with a recombination frequency of 0.4. Both genes segregate dominant (C and D) and recessive alleles (c and d). The parental cross CCDD x ccdd is performed and then the F1 progeny is testcrossed to ccdd. If 10 individuals are counted in the F2, how many are expected to be dominant for BOTH genes?
none of the above
A cross of two Drosophila strains of genotypes z+ t+ and z t produced the following progeny: 126 z+ t+, 133 z t, 15 z+ t, and 18 z t+. What is the frequency of recombination between genes t and z?
none of these choices
In the Chinese primrose, the alleles A and a result in blue-colored versus slate-colored flowers, B and b in green vs. red stigma, and C and c in short vs. long style. All 3 genes involved are on the same chromosome. A pure-breeding blue-colored, green-stigma, short-style strain was crossed to a pure-breeding slate-colored, red-stigma, long-style strain. The heterozygous F1 strain was testcrossed to a triply homozygous recessive strain. The progeny are as follows: Flower Stigma Style Number of progeny blue green long 14 blue green short 224 slate green long 142 slate green short 118 slate red long 226 blue red long 122 slate red short 16 blue red short 138 The map distance between the genes A/a and B/b is
none of these choices
The maximum recombination frequency between two genes is
none of these choices
In a three-factor cross involving linked genes, two of the eight possible phenotypes will be _____, while the other six phenotypes will be _____.
nonrecombinant; recombinant
In Morgan's three-factor fly crosses, he observed a higher proportion of a _____ pattern of traits in the F2 generation.
nonrecombnant
In a three-factor cross, double cross-over recombinants
occur less frequently than any of the single crossovers.
Crossing over occurs during _____ of meiosis I.
prophase
In humans, the genes for fibroblast growth factor receptor 1 and lipoprotein lipase are both on chromosome B. Therefore these genes are
syntenic.
In developing a hypothesis to explain Morgan's fly data, we assume that
the alleles question follow the law of segregation and the four phenotypes produced by his crosses are equally viable.
The null hypothesis for chi square analysis of a two factor cross states that
the genes in question are not linked.
According to Morgan's fly experiment, crossing over was more likely to occur if
two genes were far apart on the X chromosome.
In Drosophila melanogaster, the wild-type eye color is red. White eyes is a recessive mutation. Which of the following genotypes will exhibit a white eye phenotype?
w w