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Exam 14: Genetic Mapping in Eukaryotes

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Question 1

True/False

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Two genes that are located far from each other on the same chromosome will show a higher frequency of recombination than two genes that are close together on the chromosome.

A) True
B) False

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Question 2

Multiple Choice

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During a dihybrid cross involving two linked genes,18% of the resulting gametes showed a recombinant genotype.These two linked genes are ________ map units apart.

A) 0.18
B) 18
C) 32
D) 180
E) 1.8

F) A) and B)
G) B) and D)

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B

Question 3

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The genotypes and numbers of progeny resulting from a testcross are as follows: $\begin{array} { l r } t ^ { + g {+} l {+} }& 72 \\t g l & 69 \\t ^ { + g l } & 21 \\\operatorname { tg }^{ + l + }& 18 \\t ^ { + g l +} & 9 \\\operatorname { t}{g } ^+ l & 8 \\t ^ { +g + l }& 2 \\\text { tg}l^{+} & 1 \\\text { Total } & 200\end{array}$ Calculate the genetic distance between genes g and l.

Given three genes in order x y z,it is more accurate to measure the distance between x and z directly than to add up the shorter distances between x and y and y and z.

In a particular breed of flowering plants,two genes on the same chromosome determine flower color and leaf color.For flower color,blue (B)is dominant to pink (b),and for leaf color,white (W)is dominant to green (w).A true-breeding plant with blue flowers and white leaves is crossed with a plant that has pink flowers and green leaves.The offspring are observed and the following phenotypes are tallied. blue flowers and white leaves: 370 plants blue flowers and green leaves: 14 plants pink flowers and white leaves: 12 plants pink flowers and green leaves: 363 plants What is the frequency of recombination between these two genes?

Parental strains are always homozygous dominant for all genes or homozygous recessive for all genes.

In a species of Drosophila,genes q and r are found on the same chromosome 20 centimorgans apart.A cross was made between the following individuals: What proportion of the offspring would you expect to have the wild-type phenotype?

Is it possible to correct for the effects of multiple crossovers in calculating map distances by applying a linear mapping function.

In the offspring resulting from an F₁ testcross,what percentage of recombinant phenotypes is expected if the genes under study are independently assorting?

Interference is a phenomenon in which

When does crossing-over occur?

One map unit is equal to a recombination frequency of

A female fruit fly with the recessive mutant phenotype of white eyes and miniature wings is mated with a male possessing the wild-type phenotype of red eyes and normal wings.Among the F₁s,all the females are wild-type while all the males exhibit the mutant phenotype.The F₂s resulting from a testcross exhibit predominantly (63%)parental phenotypes.How do you explain these results?

A testcross of trihybrid Drosophila produced the following phenotypes and number of offspring. A table showing phenotype and the number of offspring with each phenotype is below. A plus sign is used for wild-type phenotype; a letter indicates the mutant phenotype for that gene. $\begin{array} { l r } + + + & 669 \\a b c & 653 \\+ + c & 121 \\a b + & 139 \\+ b + & 2280 \\a + c & 2215 \\+ b c & 3 \\a + + & 2\end{array}$ -Without performing any calculations,which of the following is the gene order?

How many phenotypic classes may be generated from a three-point testcross?

Here is a genetic map: A 18 mu B 10 mu C . AAbbCC is crossed to aaBBcc to produce an F₁ generation. If you produce 1000 offspring from testcrossing the F₁,what genotypes do you expect,and in what numbers? Assume that there is no interference.

An F₁ plant with the genotype DdGg is mated to a ddgg plant.The resulting seeds are planted and the following phenotypes produced in these numbers: DG 47 Dg 396 dG 412 dg 55 a.What were the genotypes of the parental strains that produced the F₁? b.What is the distance between the genes?

If two genes are not linked,then the expected phenotypic ratio resulting from a testcross is

Crossing-over is

X, Y, and Z are linked genes. Based on testcross data, the frequency of recombination between genes X and Y was determined to be 33.1 map units. Between genes X and Z, the distance was 11.8 mu; between genes Y and Z, the distance was 21.3 mu. -Is it possible for crossing-over to occur between two linked genes,yet for all of the resulting offspring to have parental genotypes?