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Name the individual whose work in the mid-1800s contributed to our understanding of the particulate nature of inheritance as well as the basic genetic transmission patterns. With what organism did this person work?
A recessive allele in tigers causes the white tiger. If two normally pigmented tigers are mated and produce a white offspring, what percentage of their remaining offspring would be expected to have normal pigmentation?
What types of phenotypic ratios are likely to occur in crosses when dealing with a single gene pair where all the genotypic combinations are of equal viability?
B. 1:2:1, 3:1
The fundamental Mendelian process that involves the separation of contrasting genetic elements at the same locus is called
In peas, gray seed color is dominant to white. For the purposes of this question, assume that Mendel crossed plants with gray seeds with each other and the following progeny were produced: 320 gray and 80 white.
(a) What is the most probable genotype of each parent?
(b) What genotypic and phenotypic ratios are expected in the progeny of such a cross?
a) using the symbols G = gray and g = white, Gg X Gg
(b) genotypic = 1:2:1, phenotypic = 3:1
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene (a). Two parents with normal pigmentation have an albino child.
(a) What is the probability that their next child will be albino?
(b) What is the probability that their next child will be an albino girl?
(c) What is the probability that their next three children will be albino?
(b) 1/4 X 1/2 = 1/8
(c) 1/4 X 1/4 X 1/4 = 1/64
Under what conditions does one expect a 9:3:3:1 ratio?
Answer: dihybrid cross (F2) with independently assorting, completely dominant genes
How many different kinds of gametes will be expected by an individual with the genotype PpCcTTRr?
In studies of human genetics, usually a single individual brings the condition to the attention of a scientist or physician. When pedigrees are developed to illustrate transmission of the trait, what term does one use to refer to this individual?
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene (a). Two parents with normal pigmentation have an albino child. What is the probability that their next child will be an albino girl?
Assuming independent assortment, what proportion of the offspring of the cross AaBbCcDd X AabbCCdd will have the aabbccdd genotype?
To test Mendel’s law of segregation, the experimenter needs a minimum of two contrasting forms of a gene.
To test Mendel’s law of independent assortment, the experimenter needs a minimum of two different genes and their two alleles.
Assuming complete dominance, a 3:1 phenotypic ratio is expected from a monohybrid sib or self-cross.
A situation in which there are more than two alternative forms of a given gene is called ________.
A. multiple alleles
B. alternation of generations
D. incomplete dominance
A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.
E. additive alleles
Hemizygosity would most likely be associated with which of the following?
B. incomplete dominance
C. trihybrid crosses
D. X-linked inheritance
E. sex-limited inheritance
Assume that a dihybrid cross (AaBb X AaBb) is made in which the gene loci are autosomal, independently assorting, and incompletely dominant. What phenotypic ratio would you expect from such a cross? Provide just the ratio, not the phenotypes.
In the mouse, gene A allows pigmentation to be deposited in the individual coat hairs, while its allele a prevents such deposition of pigment, resulting in an albino. Gene B gives agouti (wild-type fur), while its allele b gives black fur.
(a) Diagram the cross between a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse.
(b) What would be the expected phenotypic ratio in the progeny?
(a) AaBb X aabb
(b) 1 (agouti): 1 (black): 2 (albino)
The following F2 results occur from a typical dihybrid cross:
purple: A_B_ 9/16
white: aaB_ 3/16
white: A_bb 3/16
white: aabb 1/16
If a double heterozygote (AaBb) is crossed with a fully recessive organism (aabb), what phenotypic ratio is expected in the offspring?
Answer: 3 (white):1 (purple)
What types of ratios are likely to occur in crosses (F2) when one is dealing with two interacting, epistatic gene pairs?
Answer: 9:7, 9:3:4, 12:3:1, 15:1
Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. What is the probability that their first son will have hemophilia?
The genes for rose comb (R) and pea comb (P) together produce walnut comb. The fully homozygous recessive condition (rrpp) produces the single comb. Assume that a rose comb chicken is crossed with a walnut comb chicken and the following offspring are produced: 17 walnut, 16 rose, 7 pea, 6 single.a) What are the probable genotypes of the parents?(b) Give the genotypes of each of the offspring classes
(a) Rrpp X RrPp
(b) R-Pp (walnut)
A particular cross gives a modified dihybrid ratio of 9:7. What phenotypic ratio would you expect in a testcross of the fully heterozygous F1 crossed with the fully recessive type? Diagram the testcross using A,a,B,b as symbol sets.
The enzyme glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive gene on the X chromosome in humans. A phenotypically normal woman (whose father had G6PD) is married to a normal man.
(a) What fraction of their sons would be expected to have G6PD?
(b) If the husband had G6PD, would it make a difference to your answer in part (a)?
A cross was made between homozygous wild-type female Drosophila and yellow-bodied male Drosophila. All of the resulting offspring were phenotypically wild-type. Offspring of the F2 generation had the following phenotypes:
Sex Phenotype Number
male wild 96
male yellow 99
female wild 197
Based on this information:
(a) Is the mutant gene for yellow body behaving as a recessive or a dominant?
(b) Is the yellow locus on an autosome or on the X chromosome?
In a mating between individuals with the genotypes IAIB X IOIO, what percentage of the offspring are expected to have the O blood type?
Regarding the ABO blood group system in humans, if an individual is genetically IBIO and yet expresses the O blood type, it is likely that that individual has the _______ genotype.
A typical epistatic ratio is 9:3:4.
Assume that a mutation occurs in the gene responsible for the production of hexosaminidase A, such that only about 50% of the enzyme activity is found in the heterozygote compared with a homozygous normal individual. If heterozygotes are phenotypically normal, we would say that the mutant allele is recessive to its normal allele.
Name two forms of recombination in bacteria.
A. lytic and lysogenic
B. auxotrophic and prototrophic
C. conjugation and transduction
D. mixed and generalized
E. insertion and replication
Bacteriophages engage in two interactive cycles with bacteria. What are these cycles?
A. lytic and lysogenic
B. insertion and replication
C. auxotrophic and prototrophic
D. heteroduplex and homoduplex
E. negative and positive
A bacteriophage that is capable of entering either a lytic or lysogenic cycle is called a(an)
A. temperate bacteriophage.
B. virulent bacteriophage.
E. plaque-forming unit.
Name the general category into which double-stranded circular extrachromosomal DNA elements such as F factors, ColE1, and R fall.
D. partial diploid
Jacob, Wollman, and others developed a linkage map of E. coli that is based on time. What form of recombination is involved in generating a linkage map based on time?
Answer: Conjugation: An Hfr bacterium conjugating with an F– strain allows one to generate a map that is dependent on the passage of the donor chromosome across a conjugation tube.
Distinguish between F+ and F– bacteria.
Answer: F+ bacteria contain an F factor or plasmid that is capable of initiating conjugation.
How does an auxotroph differ from a prototroph?
Answer: Auxotrophs have lost, through mutation, the ability to grow on minimal medium.
What are the roles of the recBCD genes?
In general, what two methods are used to grow bacteria in the laboratory?
Name three forms of recombination in bacteria.
Answer: conjugation, transformation, and transduction
Name the typical phases of the bacterial growth cycle in liquid culture medium.
Answer: lag, log (exponential), and stationary
Bacteria that are in a particular physiological state to become transformed are called ________.
What is meant by the term cotransformation?
What is a merozygote?
In a bacterial cross where the donor (Hfr) is a+b+ and the recipient strain (F–) is a–b–, it is expected that recombinant bacteria will all be a+b+.
An Hfr cell can initiate chromosome transfer from one E. coli to another.
Cotransduction of genes is an indication that the genes are linked.
Lysogeny is a process that occurs during transformation and conjugation.
Viral mutations and variants are often categorized by changes in host range and/or plaque morphology.
When two genes fail to assort independently, the term normally applied is ________.
A. discontinuous inheritance
B. Mendelian inheritance
D. tetrad analysis
E. dominance and/or recessiveness
Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 106 AaBb, 48 Aabb, 52 aaBb, 94 aabb. These results are consistent with the following circumstance:
A. sex-linked inheritance with 30% crossing over.
B. linkage with 50% crossing over.
C. linkage with approximately 33 map units between the two gene loci.
D. independent assortment.
E. 100% recombination.
Assume that, regarding a particular gene, one scored 30 second-division ascospore arrangements and 70 first-division arrangements in Neurospora. What would be the
map distance between the gene and the centromere?
The genes for mahogany eyes and ebony body are approximately 25 map units apart on chromosome III in Drosophila. Assume that a mahogany-eyed female was mated to an ebony-bodied male and that the resulting F1 phenotypically wild-type females were mated to mahogany, ebony males. Of 1000 offspring, what would be the expected phenotypes, and in what numbers would they be expected?
Phenotypically wild-type F1 female Drosophila, whose mothers had light eyes (lt) and fathers had straw (stw) bristles, produced the following offspring when crossed to homozygous light-straw males:
Compute the map distance between the light and straw loci.
Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body. The F1 Lobe females were then backcrossed with homozygous smooth abdomen, straw body males, and the following phenotypes were observed:
smooth abdomen, straw body 820
smooth abdomen, Lobe 42
straw body 58
smooth abdomen 148 Lobe, straw body 152
(a) Lobe is in the middle.
smooth abdomen---5---Lobe-----------15-------------straw body
In Drosophila, assume that the gene for scute bristles (s) is located at map position 0.0 and that the gene for ruby eyes (r) is at position 15.0. Both genes are located on the X chromosome and are recessive to their wild-type alleles. A cross is made between scute-bristled females and ruby-eyed males. Phenotypically wild-type F1 females were then mated to homozygous double mutant males, and 1000 offspring were produced. Give the phenotypes and frequencies expected.
Answer: scute = 425; ruby = 425; wild-type = 75; scute-ruby = 75
To what scientific activities do the terms synkaryon and heterokaryon refer?
Answer: cell (heterokaryon) and nuclear (synkaryon) fusion and gene mapping in eukaryotes
a) In a three-point mapping experiment, what three general classes of offspring are expected (assuming crossovers occur)? (b) How many different genotypic classes are expected?
(a) Noncrossovers, single crossovers, double crossovers
What is the expected evolutionary significance of genetic recombination?
Two lines of work indicated that crossing over actually involves breakage and reunion of chromatid material. What organisms were involved, and who did the work?
In the early 1900s, two scientists noted that there were many more genes than chromosome pairs, thus setting the stage for the suggestion that some gene loci might be linked during meiotic processes. Who were these two scientists?
Answer: Walter Sutton and Theodor Boveri
What is the relationship between the degree of crossing over and the distance between two genes?
Answer: It is direct: as the distance increases, the frequency of recombination increases.
The cross GE/ge X ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103. From these data one can conclude that the recombinant progeny are gE/ge and Ge/ge.
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