Chapter 6 Flashcards
1
Q
What is a synteny group?
A
A group of genes that are found in the same order on the chromosomes of different species.
2
Q
What is genetic linkage or linkage groups?
A
A group of genes that are linked together because they are found on the same chromosome.
3
Q
The number of linkage groups is equal to what?
A
The number of chromosome types.
4
Q
Humans have how many autosomal linkage groups?
A
22
5
Q
What other linkage groups do humans have?
A
x chromosome linkage groups
Y chormosome linkage group.
6
Q
What did William Bateson and Reginald Punnett study in 1905?
A
How genes are not assorted independently.
7
Q
What was Bateson and Punnett’s study?
A
On Sweet Pea plants and flower color and pollen shape. The F2 generation did not follow the 9:3:3:1 ratio. They had a greater proportion of the two phenotypes found in the parental generation. They determined that the two characteristics were coupled.
8
Q
Which types of offspring are found in excess based on Mendel’s law of independent assortment in Bateson and Punnett’s study?
A
Purple flowers, long pollen, and red flowers, round pollen.
9
Q
Genetic linkage occurs because
a. genes that are on the same chromsome may affect the same character.
b. genes that are close together on the same chromosome tend to be transmitted together to offspring
c. genes that are on different chromsomes are independently assorted.
d. none of the above.
A
b. genes that are close together on the same chromosome tend to be transmitted together to offspring
10
Q
In the experiment by Bateson and Punnett, which of the following observations suggested linkage in the sweet pea?
a. a 9:3:3:1 ratio was observed in the F2 offspring
b. a 9:3:3:1 ratio was not observed in the F2 offspring
c. an unusually high number of F2 offspring had phenotypes of the parental generation.
d. both b and c suggested linkage.
A
d. both b and c suggested linkage.
11
Q
Even though the alleles for different genes may be linked along the same chromosome, the linkage can be what?
A
Altered during meiosis.
12
Q
What is crossing over?
A
A physical exchange of chromosome pieces that most commonly occurs during prophase of meiosis I.
13
Q
What is a bivalent?
A
A structure in which two pairs of homologous sister chromatids have synapsed with each other.
14
Q
If a crossover began in the short region between gene A and the tip of the chromosome, would this event affect the arrangment of the A and B alleles?
A
No, such a crossover would not change the arrangements of these alleles.
15
Q
What is genetic recomination?
A
- The process in which chromosomes are broken and then rejoined to form a nove genetic combination
- The process in which alleles are assorted and passed to offspring in combinations that are different from the parents.
16
Q
What are recombinant cells?
A
a. Combinations of alleles or traits that are not found in the parental generations.
b. DNA molecules that are produced by molecular techniques in which segments of DNA are joined to each other in ways that differ from their original arrangment in their native chromosomal sites.
17
Q
What are recombinant offspring?
A
The offspring of haploid cells that were gamates that participated in genetic recombination.
18
Q
What are nonrecombinant offspring?
A
Offspring that have inherited the same combination of alleles found in the chromosomes of their parents.
19
Q
What did Thomas Hunt Morgan study in 1911?
A
The inheritance pattern of different characters that have been shown to follow an x-linked pattern of inheritance.
Fruit flies with red and white eyes.
20
Q
Of the eight possible phenotypic combinations in the F2 generation, which ones are the product of a single crossover in Morgan’s Fruit fly study?
A
Single cross can produce: Gray body, red eyes, miniature wings
Gray body, white eyes, miniature wings;
Yellow body, red eyes, long wings;
yellow body, white eyes, long wings.
21
Q
Why are the types of offspring described in part (b) involving crossover between eye color and wing length genes more numerous than those described in part (c) involving crossover between body color and eye color genes?
A
When genes are relatively close togehter, a corssover is relatively unlikely to occur between them. Therefore, nonrecombinant offspring are more common.
22
Q
What determines the proportions of recombinant offspring?
A
The distance between the two genes.
23
Q
Why are the nonrecombinant offspring more common than the recombinant offspring?
A
The w and m genes are farther apart than the y and w genes.
24
Q
What are the seven reasons why genetic maps are useful?
A
- understand the complexity and genetic organixation of a species.
- understand the underlying basis of inherited traits.
- clone genes
- understand evolution
- diagnose and treat disases
- provide the likelihood of acouple having offspring with genetic diseases
- agricultural breeders of livestock and crops.
25
What can be used to determine if two genes are linked or independently assorted?
chi square test.
26
How do you begin determining whether genes are linked or indpendently assorted?
Begin with the hypothesis that the genes are not linked.
If the chi square value is low we cannot reject the null hypothesis, we infer that the genes are independently assorted. If the chi square value is high, then we accept the alternative hypothesis that the genes are linked.
27
What other factor could provide a false acceptance of linked genes?
Decreased viability of particular phenotypes is actually independent assortment
28
What are the steps for applying the chi square test?
Propose a hypothesis
Based on the hypothesis, calculate the expected value of each of the four phenotypes.
Apply the chi square formula, using the data for the observed values and the expected values that have been calculated.
Interpret the calculated chi square value.
29
In Creighton and McClintock's experiement, involving the corsses of two linked genes to produce nonrecombinant and recombinant offspring, what two types of characteristics can crossing over change? Hint: one type is seen only with a microscope, whereas the other type can be seen with the unaided eye.
Crossing over can change the combination of kernel phenotypes and also it can change the morphologies of the chromosomes compared to the parental chromsomes.
30
Creighton and McClintock began with what in their experiment?
A corn strain that carried an abnormal chromosome that had a knob at one end and a translocation at the other. It was Cwx
31
With regard to linked genes along the same chromosome, which of the following statements is false?
a. crossing over is needed to produce nonrecombinant offspring.
b. crossing over is needed to produce recombinant offsrping
c. corssing over is more likely to separate alleles if they are far apart on the same chromosome.
d. crossing over that separates inked alleles occurs during prophase of meiosis I.
a. crossing over is needed to produce nonrecombinant offspring.
32
Morgan observed a higher number of recombinant offspring involving eye color and wing length (401 +318) than recombinants for body color and eye color (17 + 12). These results occurred because
a. the genes affecting eye color and wing length are farther apart on the x chromsome than are the genes affecting body color and eye color.
b. the genes affecting eye color and wing length are closer together on the x chromosome than are the genes affecting body color and eye color.
c. the gene affecting wing length is not on the x chromosome.
d. the gene affecting body color is not on the x chromosome.
a. the genes affecting eye color and wing length are farther apart on the x chromsome than are the genes affecting body color and eye color.
33
In a chi square analysis involving genes that may be linked, which of the following statements is correct?
a. an independent assortment hypothesis is not proposed because the data usually suggest linkage.
b. an independent assortment hypothesis is proposed because it allows you to calculate expected number of offspring.
c. a large chi square value suggests that the observed and expected data are in good agreement.
d. the null hypothesis is rejected when the chi square value is very low.
b. an independent assortment hypothesis is proposed because it allows you to calculate expected number of offspring.
34
What are the other names for Genetic mapping?
Gene mapping
| Chromosome mapping
35
What is the purpose of genetic mapping?
To determine the linear order and distance of separation among genes that are linked to each other along the same chromosome.
36
What is locus?
The physical location of a gene within a chromosome.
37
Why is genetic mapping useful?
It allows geneticist to understand the overall complexity and genetic organization of a particular species.
It displays the inherited traits an organism displays
The locus of a gene can help molecular geneticists to clone that gene.
Useful for evolutionary understanding
Can help treat inherited diseases.
38
Genetic mapping is based on what?
The level of recombination that occurs in just one parent
39
When and in which fly or flies did corssing over occur in order to produce the recombinant offspring when dealing with fruit flies with long or short bristles and black or gray body color.
Crossing over occurs during oogenesis in the female parent of the recombinant offspring.
40
What is the map distance?
The relative distance between sites along a single chromsome.
41
What is the equation for map distance?
Map distance= (number of recombinant offspring/total number of offspring) X 100
42
What is the unit of distance for map distance?
```
Map units (mu) or
centiMorgans (cM)
```
43
A testcross is expected to yield a maximum of only what percent of recombinant offspring?
50%
44
What phenomenon explains why the maximum percentage of recombinant offspring does not exceed 50%?
Multiple crossovers prevent the maximum percentage of recombinant offspring from exceeding 50%.
45
The double crossover is always expected to be what?
least frequent category of offspring.
46
The combination of traits in the double crossover tells us what?
Which gene is in the middle.
47
When a chromatid undergoes a double crossover, what happens to the gene in the middle.
It becomes separated from the other two genes at either end.
48
To construct a genetic map, we use the distance between what?
The genes that are closest together.
49
How does the map distance map equation change when performing a double crossover?
Add the the number of offspring due to double crossovers and multiply that by two at the top of the equation.
50
How do you compute the crossover frequency?
Map distance/100.
51
How do you determine the number of expected offspring based on the crossover frequency?
Multiple the two crossover frequency numbers together to get the percentage of offspring.
52
What is positive interference?
The phenomenon in which a crossover that occurs in one region of a chromosome decreases the probability that another crossover will occur nearby.
53
what interfers with the ability for genes to form a second crossover in the immediate vicinity?
The first crossover interfers.
54
What is the coefficient of coincidence (C)?
The ratio of observed number of double crossovers to the expected number.
55
What is the equation for coefficient of coincidence?
C= observed number of crossovers/expected number of double crossovers.
56
How do you calculate interference?
I= 1 -C
57
Parental generation: True-breeding flies with red eyes and long wings were crossed to flies with white eyes and miniature wings. All F1 offspring had red eyes and long wings.
The F1 female flies were then crossed to males with white eyes and miniature wings. The following results were obtained for the F2 generation:
129 red eyes, long wings
133 white eyes, minature wings
71 red eyes, minature wings
67 white eyes, long wings.
What is/are the phenotype(s) of the recombinant offspring of the F2 generation?
a. Red eyes, long wings
b. white eyes, miniature wings
c. Red eyes, long wings and white eyes, miniature wings.
d. Red eyes, miniature wings and white eyes, long wings.
d. Red eyes, miniature wings and white eyes, long wings.
58
Parental generation: True-breeding flies with red eyes and long wings were crossed to flies with white eyes and miniature wings. All F1 offspring had red eyes and long wings.
The F1 female flies were then crossed to males with white eyes and miniature wings. The following results were obtained for the F2 generation:
129 red eyes, long wings
133 white eyes, minature wings
71 red eyes, minature wings
67 white eyes, long wings.
The recombinant offspring of the F2 generation were produced by crossing over that occured
a. during spermatogenesis in the parental generation males.
b. during oogenesis in the parental generation females
c. during spermatogenesis in the F1 males.
d. during oogenesis in the F1 females.
d. during oogenesis in the F1 females.
59
Parental generation: True-breeding flies with red eyes and long wings were crossed to flies with white eyes and miniature wings. All F1 offspring had red eyes and long wings.
The F1 female flies were then crossed to males with white eyes and miniature wings. The following results were obtained for the F2 generation:
129 red eyes, long wings
133 white eyes, minature wings
71 red eyes, minature wings
67 white eyes, long wings.
What is the map distance between these two genes?
a. 32.3mu
b. 34.5mu
c. 16.2mu
d. 17.3mu
b. 34.5mu
60
most of the earliest understanding of genetic recombination came from the genetic analysis of what?
Sac Fungi
61
Fungal cells are usually what type of cells and how do they reproduce?
Haploid cells
| Asexually
62
What are spores?
Haploid cells that are produced by certain species, such as fungi yeast and molds.
63
What is a tetrad, not to be confused with a tetrad of four sister chromatids.
A group of four fungal spores contained within an ascus.
64
What is octad?
A group of eight fungal spores contained within an ascus.
65
In ascomycete fungi and certain species of algaie, the cells of a tetrad or octad are contained where?
In a sac called an ascus.
66
What is contained in one ascus?
The products of a single meiotic division are contained within one sac.
67
What within an ascus varies from species to species?
The arrangement of spores.
68
What is an unordered tetrad or octad?
An ascus composed of four unordered cells.
69
How are unordered tetrad or octad created?
When some ascus provides enough space for the tetrads or octads of spores to randomly mix together.
70
What are ordered tetrads and octads?
An ascus composed of four cells whose order depends on crossing over during meiosis.
71
How does ordered tetrads and octads occur?
When the ascus is tight and prevents spores from randomly moving around.
72
What is a parental ditype (PD)
An ascus that contains four spores with the parental combinations of alleles.
73
What is a tetratype (T)?
An ascus that has two parental cells and two nonparental cells.
74
What is a nonparental ditype (NPD)?
An ascus that contains cells that all have a nonparental combination of alleles.
75
What percent of asci yield recombinant spores?
50%, the number of asci having a parental ditype is expected to equal the number having a nonparental ditype.
76
A single crossover event of asci produces what?
A tetratype.
77
Double crossover events in asci produce what?
A parental ditype, tetratype, or nonparental ditype.
78
When is a nonparental ditype produced in a double crossover involving asci?
When a double crossover involves all four chromatids.
79
When is a tetratype produced in a double crossover involving asci?
A three-chromatid crossover
80
When is a parental ditype produced in a double crossover involving asci?
When two chromatids are involved.
81
How is the map distance calculated in a fungi chromosome?
Map distance= (NPD+ 1/2 T/Total number of asci) X100
82
What is the map distance calculation for double crossovers?
Map distance= )single crossover tetrads + (2XDouble crossover tetrads)/total number of asci) X .5X 100
83
An ascus called an octad is the product of
a. one meiotic division
b. two meiotic divisions
c. one meiotic division followed by one mitotic division.
d. one mitotic division followed by one meiotic division.
c. one meiotic division followed by one mitotic division.
84
One yeast strain is lys+ and arg+, whereas another strain is lys-3 and arg-2. The two strains were crossed to each other and an ascus obtained from this cross has four spores with the following genotypes: lys+ arg+, lys+ arg-2, lys-3 arg+, and lys-3 arg2. This ascus is a
a. parental ditype.
b. tetratype
c. nonparental ditype
d. could be b or c.
b. tetratype
85
Crossing over during mitosis is expected to occur _______________ frequently than during meiosis.
Much less
86
What is mitotic recombination?
Crossing over that occurs during mitosis.
87
If mitotic recombination occurs during an early stage of embryonic development, what happens?
The daughter cells containing one recombinant chromosome and one nonrecombinant chromosome will continue to divide many times to produce a patch of tissue in the adult. This may result in a portion of tissue with characteristics different from those of the rest of the organism.
88
What is a twin spot?
Places in which two adjacent regions were phenotypically different from each other and also different from the rest of the body.
89
Is twin spotting a frequent occurance?
More so, then twin spotting being explained by the random positioning of two independent single spots that happened to occur close together.
90
Curt Stern propsed twin spotting was due to what?
A single mitotic recombination within one cell during embryonic development.
91
Does mitotic recombination occur in a gamete or in a somatic cell?
Somatic cells.
92
The process of mitotic recombination involves the
a. exchange of chromosomal regions between homologs during gamete formation.
b. exchange of chromosomal regions between homologs during the division of somatic cells.
c. reassortment of alleles that occurs at fertilization.
d. reassortment of alleles that occurs during gamete formation.
b. exchange of chromosomal regions between homologs during the division of somatic cells.
93
When applying a chi square approach in a linkage problem, explain why an independent assortment hypothesis is used?
It enables us to calculate the expected values based on Mendel's ratios. Using the observed and expected values, we can calculate whether or not the deviations between the observed and expected values are too large to occur as a matter of chance. If the deviations are very large, we reject the hypothesis of independent assortment.
94
Mitotic recombination can occasionally produce a twin spot. Let's suppose an animal species is heterozygous for two genes that govern fur color and length. One gene affects pigmentation, with dark pigmentation (A) dominant to albino (a); the other gene affects hair length, with long hair (L) dominant to short hair (l). The two genes are linked on the same chromosome. Let's assume this animal is AaLl; A is linked to l, and "a" is linked to L. Draw the chromosomes labeled with these alleles, and explain how mitotic recombination could produce a twin spot with one spot having albino pigmentation and long fur, the other having dark pigmentation and short fur.
If the chromosomes 2 and 4 move into one daughter cell, that will lead to a patch that is albino and has long fur. The other cell will receive chromosomes 1 and 3, which will produce a patch that has dark, short fur.
95
Chromosomes have ABC genes on one and abc on the other. Crossover is occuring at AB and ab. Labeling goes from top to bottom of chromosome legs starting with 1 going to 4. (ABC is on the top two, abc on the bottom two.)
What is the outcome of this single crossover event? If a second crossover occurs somewhere between A and C, explain which two chromatids it would involve and where it would occur to produce the types of chromosomes shown here:
A. ABC, AbC, aBc, and abc
B. Abc, Abc, aBC, and aBC
C. ABc, Abc, aBC and abC
D. ABC, ABC, abc, and abc.
A. Between 2 and 3, between genes B and C
B. Between 1 and 4, between genes A and B
C. between 1 and 4, between genes B and C
D. Between 2 and 3, between genes A and B.
96
If you try to throw a basketball into a basket, the likelihood of succeeding depends on the size of the basket. It is more likely that you will get the ball into the basket if the basket is bigger. In your own words, explain how this analogy also applies to the idea that the likelihood of crossing over is greater when two genes are far apart than when they are close together.
The chances of a crossover initiating in a region between two genes is proportional to the size of the region between the two genes. There are a finite number (usually a few) of crossovers that occur between homologous chromosomes during meiosis, and the likelihood that a crossover will occur in a region between two genes depends on how big that region is.
97
In most two-factor crosses involving linked genes, we cannot tell if a double crossover between the two genes has occurred because the offspring will inherit the nonrecombinant patter of alleles. How does the inability to detect double crossovers affect the calculation of map distance? Is map distance underestimated or overestimated because of our inability to detect double crossovers? Explain your answer.
The inability to detect double crossovers causes the map distance to be underestimated. In other words, more crossovers occur in the region than we realize. When we have a double crossover, we don not get a recombinant offspring (in a dihybrid cross). Therefore, the second crossover cancels out the affects of the first crossover.
98
Describe the unique features of ascomycetes that lend themselves to genetic analysis.
The key feature is that all the products of a single meiosis are contained within a single sac. The spores in this sac can be dissected, and then their genetic traits can be analyzed individually.
99
Explain the difference between an unordered versus an ordered octad.
In an unordered ascus, the products of meiosis are free to move around. In an ordered octad (or tetrad), they are lined up according to their relationship to each other during meiosis and mitosis.
100
How would you determine that genes in mammals are located on the Y chromosome linkage group? is it possible to conduct crosses (let's say in mice) to map the distances between genes along the Y chromosome?
A gene on the Y chromosome in mammals would be transmitted only from father to son. It would be difficult to genetically map Y-linked genes because a normal male has only one copy of the Y chromosome, so you do not get any crossing over between two Y chromosomes. Occasionally, abnormal males (XYY) are born with two Y chromosomes. If such males were heterozygous for alleles of Y-linked genes, one could examine the normal male offspring of XYY fathers and determine if crossing over has occurred.
101
In your own words, explain why a testcross cannot produce more than 50% recombinant offspring. When a testcross does produce 50% recombinant offspring, what do these results mean?
We cannot get more than 50% recombinant offspring because the pattern of multiple crossovers can yield an average maximum value of only 50%. When a testcross does yield a value of 50% recombinant offspring, it can mean two different things. Either the two genes are on different chromosomes or the two genes are on the same chromosome but at least 50mu apart.
102
If two genes are more than 50mu apart, how would you ever be able to show experimentally that they are ocated on the same chromosome?
You would need to map genes between them to show that the two genes were actually in the same linkage group.
