Question 1

Which step is catalyzed by the enzyme responsible for the Met 2 mutant? $\begin{array} { l  } \text { Growth Medium }\
\hline \begin{array} { l  } 
 \text { Mutant }\ \text {strain }\
\end{array}&\begin{array} { l  } 
 \text { Minimal}\ \text { medium}\
\end{array}&\begin{array} { l  } 
 \text { Minimal+}\ \text {cysteine }\
\end{array}&\begin{array} { l  } 
 \text { Minimal+}\ \text {cystathionine }\
\end{array}&\begin{array} { l  } 
 \text {Minimal+ }\ \text {homocysteine }\
\end{array}&\begin{array} { l  } 
 \text { Minimal+}\ \text { methionine}\
\end{array}&\begin{array} { l  } 
 \text { Compound}\ \text {  accumulating}\ \text {  in mutant}\
\end{array}\
\hline
\begin{array} { l  } 
 \text { Control}\ \text {prototroph }\
\end{array}&+&+&+&+&+& \text {None }\
\text { Met } 1&-&-&-&-&+&\text { Homocysteine }\
\text { Met } 2&-&-&-&+&+&\text { Cystathionine }\
\text { Met } 3&-&-&+&+&+&\text { Cysteine }\
\text { Met } 4&-&+&+&+&+&\text { Homoserine }\
\end{array}$

Accepted Answer

The answer of Which step is catalyzed by the enzyme...

Question 2

What are the three categories of loss- of- function mutations?

Accepted Answer

The answer of What are the three categories of loss-...

Question 3

In yeast, there are three gene products required to synthesize the amino acid lysine. You cross two haploid lysine auxotrophs to form a diploid. The diploid fails to grow on plates lacking lysine. Which of the following can you definitively conclude?

Accepted Answer

The diploid's inability to grow on lysine-free media indicates that both haploid strains have mutations in the same gene, preventing complementation and thus lysine synthesis.

Question 4

Wild- type bacteria can grow on minimal medium. Four mutants that cannot grow on minimal med but can grow on minimal medium supplemented with the nutrient "H" are isolated. It is suspected t metabolites T, P, and A are in the biochemical pathway for synthesis of H, so each mutant is tested f ability to grow on minimal medium supplemented with these metabolites: 
A. Mutant 1: can grow on minimal medium supplemented with T, but not P or A
B. Mutant 2: is unable to grow on minimal medium supplemented with T, P, or A
C. Mutant 3: is able to grow on minimal medium supplemented with A or T, but not P
D. Mutant 4: can grow on minimal medium supplemented with T, P, or A.
Which of the following is NOT consistent with this information?

Accepted Answer

The answer of Wild- type bacteria can grow on minimal...

Question 5

In the biosynthetic pathway for conversion from homoserine to methionine, you identify a Neurospora crassa double mutant Met1/Met2. This mutant will grow only if which supplement(s) are added to the minimal media?
 $\begin{array} { l  } \text { Growth Medium }\
\hline \begin{array} { l  } 
 \text { Mutant }\ \text {strain }\
\end{array}&\begin{array} { l  } 
 \text { Minimal}\ \text { medium}\
\end{array}&\begin{array} { l  } 
 \text { Minimal+}\ \text {cysteine }\
\end{array}&\begin{array} { l  } 
 \text { Minimal+}\ \text {cystathionine }\
\end{array}&\begin{array} { l  } 
 \text {Minimal+ }\ \text {homocysteine }\
\end{array}&\begin{array} { l  } 
 \text { Minimal+}\ \text { methionine}\
\end{array}&\begin{array} { l  } 
 \text { Compound}\ \text {  accumulating}\ \text {  in mutant}\
\end{array}\
\hline
\begin{array} { l  } 
 \text { Control}\ \text {prototroph }\
\end{array}&+&+&+&+&+& \text {None }\
\text { Met } 1&-&-&-&-&+&\text { Homocysteine }\
\text { Met } 2&-&-&-&+&+&\text { Cystathionine }\
\text { Met } 3&-&-&+&+&+&\text { Cysteine }\
\text { Met } 4&-&+&+&+&+&\text { Homoserine }\
\end{array}$

Accepted Answer

The answer of In the biosynthetic pathway for conversion from...

Question 6

Gene interactions in which an allele of one gene modifies or prevents expression of alleles of another gene is known as_______ .

Accepted Answer

Epistasis occurs when the expression of one gene is affected by the presence of one or more 'modifier genes'.

Question 7

In sheep, coat color is influenced by two genes. Gene A influences pigment production, while gene B produces black or brown pigment. If two heterozygous white sheep resulted in 12 white sheep, 3 black sheep, and 1 brown sheep, which genotype(s) of the white sheep explain this data?

Accepted Answer

The white sheep could be A_B_ or A_bb.The white sheep must have at least one recessive allele for both genes. The black sheep must have two dominant alleles for gene B, and the brown sheep must have two recessive alleles for gene B. The only genotype of the white sheep that can explain this data is A_B_ or A_bb.

Question 8

King George III of England and other members of the royal family were afflicted with a series of strange, seemingly unrelated symptoms including abdominal pain, rapid pulse, convulsions, and insanity. It has been determined that he likely suffered from porphyria, caused by a mutation in a single allele. What is the genetic term describing the alteration of multiple, distinct traits of an organism by a mutation in a single gene?

Accepted Answer

Pleiotropy refers to the phenomenon where a single gene influences multiple phenotypic traits, which explains the variety of symptoms experienced by King George III from a mutation in just one gene.

Question 9

Bateson and Punnett crossed two white- flowered lines and saw all purple flowers in the F1 generat They concluded this was an example of complementary gene interactions because a cross of the F1 plants yielded what ratio in the F2 generation?

Accepted Answer

The correct answer is D) 9 purple to 7 white. This is because in complementary gene interactions, two different genes work together to produce a phenotype. If an organism is homozygous recessive for either gene, it will not display the dominant phenotype. In this case, purple flowers are produced only when both genes are present in at least one dominant form (A_B_). The F2 generation from a dihybrid cross in such a scenario typically shows a phenotypic ratio of 9:7 (9 showing the dominant phenotype and 7 showing the recessive phenotype), indicating complementary gene interaction.

Question 10

Two pure- breeding mutant plants produce white flowers. When they are crossed, all of the progeny have wild- type purple flowers. What does this genetic complementation tell you?

Accepted Answer

This genetic complementation indicates that more than one gene is involved in determining the phenotype, as the two mutant plants have mutations in different genes that complement each other to produce the wild-type phenotype in the progeny.

Question 11

Wild- type bacteria can grow on minimal medium. Four mutants that cannot grow on minimal med but can grow on minimal medium supplemented with the nutrient "H" are isolated. It is suspected t metabolites T, P, and A are in the biochemical pathway for synthesis of H, so each mutant is tested f ability to grow on minimal medium supplemented with these metabolites: 
A. Mutant 1: can grow on minimal medium supplemented with T, but not P or A
B. Mutant 2: is unable to grow on minimal medium supplemented with T, P, or A
C. Mutant 3: is able to grow on minimal medium supplemented with A or T, but not P
D. Mutant 4: can grow on minimal medium supplemented with T, P, or A.
Which of the following is NOT consistent with this information?

Accepted Answer

The answer of Wild- type bacteria can grow on minimal...

Question 12

A certain species of morning glories produces flowers that are blue, red, or purple. Two pure- breeding purple lines are crossed and produce F1 progeny that all make blue flowers. The F1 allowed to self and produce 320 F2 progeny with the following distribution: 185 blue, 115 purple, an red.
Which the following is NOT consistent with this information?

Accepted Answer

The answer of A certain species of morning glories produces...

Question 13

Are loss- of- function mutations more likely to be dominant or recessive?

Accepted Answer

The answer of Are loss- of- function mutations more likely...

Question 14

Deafness is caused by recessive mutations in any one of at least five genes. Two deaf individuals have nine children, all of whom have normal hearing. Which of the following can you conclude?

Accepted Answer

Since all nine children have normal hearing, it suggests that each parent carries mutations in different genes responsible for hearing. In this scenario, each child would inherit one normal allele from each parent for each of the genes involved, thus not exhibiting deafness. This is consistent with the idea that the parents have mutations in different genes, allowing for the possibility of producing offspring with normal hearing when those different genes complement each other.

Question 15

You are looking at the color of feathers in ducks and find that yellow ducks (Y) are dominant to green ducks (y). However, a second gene, H, controls whether the color will be expressed in the feathers. If the duck is hh, the duck will always be white, because the pigment does not go into feathers. What ratio of phenotypes would you expect following a dihybrid cross?

Accepted Answer

The correct ratio is 9:3:4, which results from a dihybrid cross where one gene affects the expression of another. In this case, 9 will be yellow (Y_), 3 will be green (yy), and 4 will be white (hh) regardless of the Y gene because hh prevents color expression.

Question 16

A metabolic reaction requires 10 units of enzymatic activity to proceed. If a dominant allele D can generate 8 units of enzyme and a recessive allele d can generate 2 units of enzyme, what can be said of the dominant wild- type allele?

Accepted Answer

The answer of A metabolic reaction requires 10 units of...

Question 17

Independent assortment predicts a 9:3:3:1 ratio with four different phenotypes in the F2 progeny. If the alleles are epistatic, what would you predict?

Accepted Answer

Epistasis can alter the phenotypic ratios expected from independent assortment by suppressing the effect of alleles at one gene due to the presence of certain alleles at another gene, often resulting in fewer distinguishable phenotypes.

Question 18

The 9:6:1 ratio seen in the dihybrid cross of summer squash indicates what genetic relationship between the two genes controlling fruit shape?

Accepted Answer

The answer of The 9:6:1 ratio seen in the dihybrid...

Question 19

A metabolic reaction requires 40 units of enzymatic activity to proceed. If a dominant allele D can generate 40 units of enzyme and a mutant allele d" generates 20 units of enzyme, what can be said of the dominant wild- type allele?

Accepted Answer

The answer of A metabolic reaction requires 40 units of...

Question 20

Complementation tests of distinct recessive mutants, 1 through 8, produce the data in the matrix below. A plus (+) indicates complementation, meaning the phenotype of the combined alleles is wild type, and a minus (- ) indicates a failure to complement meaning that a mutant phenotype results. Assume that the missing mutant combinations would yield data consistent with the entries that are shown.  How many complementation groups are formed by these eight mutants?

Accepted Answer

The answer of Complementation tests of distinct recessive mutants, 1...

Quiz 4: Inheritance Patterns of Single Genes and Gene Interaction