Question 1

Duchenne muscular dystrophy (DMD)is normally an X-linked recessive human disease affecting boys.Girls afflicted with DMD are rare.Cytogenetic studies of several girls with DMD have in each case revealed that these individuals carry X-autosome translocations.The autosomes vary, but the breakpoint on the X in every case is in band p21, which is the location of the DMD gene.Cytogenetic studies further revealed that in all cells studied in such DMD girls the normal X chromosome exists as a Barr body.How might these observations account for the existence of DMD-affected girls? Why is only the normal X seen as a Barr body?

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Question 2

A newly discovered species of dung beetle has 2n = 16 chromosomes.It mates with a closely related beetle species that has 2n = 12 chromosomes.How many chromosomes would there be in an amphidiploid beetle produced from this cross?
A)12
B)14
C)16
D)28
E)12 or 16

Accepted Answer

When two species with different diploid chromosome numbers mate, the resulting hybrid may or may not be fertile. In cases where there is enough chromosomal homology between the two species, the hybrid may produce diploid gametes through a process called somatic doubling, which can then fuse with either parental species, resulting in a fertile amphidiploid organism with twice as many chromosomes as either parent.

In this case, the two parent species have diploid chromosome numbers of 16 and 12, respectively. To get an amphidiploid beetle from their cross, we need to add their chromosome numbers together and double the result, since the hybrid will have two sets of chromosomes. That gives us:

(16 + 12) x 2 = 56

Therefore, the answer is D, 28 chromosomes.

Question 3

You are studying two different mutant fish lines (A and

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Question 4

Most strains of cultivated bananas were created by crossing plants within and between two diploid species: Musa acuminata (genome = AA)and Musa balbisiana (genome = BB).The Cavendish banana (genome = AAA), the variety most often sold in grocery stores, has what type of genome?
A)Allodiploid
B)Allotriploid
C)Autotriploid
D)Allotetraploid
E)Autotetraploid

Accepted Answer

The Cavendish banana has a genome of AAA, which suggests that it is an autotriploid banana. This means that it has three sets of chromosomes, all coming from the same species (Musa acuminata) without involvement from Musa balbisiana.

Question 5

Isochromosomes have the structure ABC^-CBA (where ^- represents the centromere, and A, B, and C represent wild-type alleles of three different genes).In some cases, such isochromosomes are derived from two copies of one-half of a metacentric chromosome, which has a centromere near its center.For example, a wild-type metacentric chromosome ABC^-DEF might form two distinct isochromosomes, ABC-CBA and FED-DEF.The centromeres of such distinct isochromosomes can be homologous, so that they cause the segregation of the two distinct isochromosomes from each other during meiosis. a.A mutant of genotype ABC-CBA/FED-DEF is viable.If you cross this mutant with a wild-type individual, what would you expect to be the genotype of the offspring? Would these offspring be viable or not? Explain. b.What would you expect if you cross this mutant with another individual of genotype ABC-CBA/FED-DEF? Explain. c.You are given a pericentric inversion mutant in which this same chromosome is of genotype ABD-CEF.In an individual heterozygous for this inversion and a wild-type chromosome there is a crossover between C and the centromere, as follows: Indicate the gametes that would be generated. d.Assume that the inversion interval is very small, so that both duplications and deletions for this interval (from C to

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Question 6

Most strains of cultivated bananas were created by crossing plants within and between two diploid species: Musa acuminata (genome = AA)and Musa balbisiana (genome = BB).Bananas with a genome of AAB are an example of which kind of polyploidy?
A)Allodiploid
B)Allotriploid
C)Autotriploid
D)Allotetraploid
E)Autotetraploid

Accepted Answer

Allotriploid organisms have three sets of chromosomes derived from different species. The AAB genome in bananas results from crossing two species (Musa acuminata and Musa balbisiana), making it an example of allotriploidy.

Question 7

Down syndrome has, in some cases, been found to run in families.Explain the genetic basis for this inherited form of the condition.

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The answer of Down syndrome has, in some cases, been...

Question 8

Explain the genetic basis for sterility in autopolyploid organisms.

Accepted Answer

The answer of Explain the genetic basis for sterility in...

Question 9

List the four basic types of chromosome rearrangements.

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Quiz 6: Chromosome Variation

A newly discovered species of dung beetle has 2n = 16 chromosomes.It mates with a closely related beetle species that has 2n = 12 chromosomes.How many chromosomes would there be in an amphidiploid beetle produced from this cross?

You are studying two different mutant fish lines (A and

Most strains of cultivated bananas were created by crossing plants within and between two diploid species: Musa acuminata (genome = AA) and Musa balbisiana (genome = BB) .The Cavendish banana (genome = AAA) , the variety most often sold in grocery stores, has what type of genome?

Most strains of cultivated bananas were created by crossing plants within and between two diploid species: Musa acuminata (genome = AA) and Musa balbisiana (genome = BB) .Bananas with a genome of AAB are an example of which kind of polyploidy?

Down syndrome has, in some cases, been found to run in families.Explain the genetic basis for this inherited form of the condition.

Explain the genetic basis for sterility in autopolyploid organisms.

List the four basic types of chromosome rearrangements.