Q: The coefficient of coincidence (C) is calculated using which of the following formulas?

$C = \frac{\text{Observed double crossovers}}{\text{Expected double crossovers}}$

Q: If the recombination frequency between genes A and B is 20 m.u. and between B and C is 10 m.u., what is the expected frequency of double crossovers between A and C?

$0.20 \times 0.10 = 0.02$ (or 2%)

Question 1

The coefficient of coincidence (C) is calculated using which of the following formulas?

Accepted Answer

$C = \frac{	ext{Observed double crossovers}}{	ext{Expected double crossovers}}$

Question 2

If the recombination frequency between genes A and B is 20 m.u. and between B and C is 10 m.u., what is the expected frequency of double crossovers between A and C?

Accepted Answer

$0.20 	imes 0.10 = 0.02$ (or 2%)

Question 3

In a testcross with 1000 progeny, the expected number of double crossovers is 20, but only 15 are observed. What is the coefficient of coincidence?

Accepted Answer

$C = \frac{15}{20} = 0.75$

Question 4

If the interference (I) is calculated as 0.59, what does this value indicate?

Accepted Answer

You will observe 59% of expected double crossovers.

Question 5

Which of the following best describes a paracentric inversion?

Accepted Answer

An inversion that does not include the centromere.

Question 6

What is the likely outcome for gametes produced from a crossover within a paracentric inversion?

Accepted Answer

Nonviable recombinant gametes due to the formation of dicentric and acentric chromatids.

Question 7

Which chromosomal abnormality is most likely to result in a phenotype due to gene dosage effects?

Accepted Answer

Duplication

Question 8

A diploid organism has $2n = 56$ chromosomes. How many chromosomes would be found in a trisomic individual of this species?

Accepted Answer

$57$

Question 9

Which of the following is NOT a way that deletions can cause abnormal phenotypes?

Accepted Answer

Haploinsufficient genes can result because too much gene product is produced.

Question 10

Which of the following chromosomal mutations would result in an individual with the chromosome composition $AAABBB$ if species I is diploid with $AABB$?

Accepted Answer

Autotriploidy in species I

Question 11

Which of the following is a likely consequence of a Robertsonian translocation in humans?

Accepted Answer

Familial Down syndrome due to fusion of chromosomes 14 and 21

Question 12

A plant breeder wants to create a new variety of wheat by combining two different species, each with a different chromosome set. What type of polyploidy is being utilized?

Accepted Answer

Allopolyploidy

Question 13

Which of the following best explains why most triploid (3n) plants are sterile?

Accepted Answer

They cannot form balanced gametes during meiosis due to uneven chromosome segregation.

Question 14

A human cell is found to have 45 chromosomes, including only one X chromosome and no Y chromosome. What is the most likely diagnosis?

Accepted Answer

Turner syndrome (XO)

Question 15

Which of the following is a direct cause of aneuploidy?

Accepted Answer

Nondisjunction during meiosis or mitosis

Question 16

If a species II is diploid with chromosomes $MMNNOO$, what would be the chromosome composition of a nullisomic individual for chromosome N?

Accepted Answer

$MMOO$

Question 17

Which of the following statements about gene dosage is correct?

Accepted Answer

Gene dosage imbalances can disrupt development by altering the amount of protein produced.

Question 18

A chromosome with two centromeres is called a:

Accepted Answer

Dicentric chromatid

Question 19

Which of the following best describes the effect of a pericentric inversion on meiosis?

Accepted Answer

It can lead to gametes with duplications and deletions if crossing over occurs within the inversion.

Question 20

A testcross is performed with a trihybrid individual for genes A, B, and C. The recombination frequencies are $r_{A-B} = 10.6$ m.u. and $r_{B-C} = 13.4$ m.u. If 1000 progeny are produced and there is no interference, how many double crossovers are expected?

Accepted Answer

$1000 	imes 0.106 	imes 0.134 = 14.2$ (about 14)

Chromosomal Variation: Coefficient of Coincidence, Interference, and Chromosomal Rearrangements

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