Chapter 13 Problems

Question 1

exact exchange of parts of two non homologous chromosoes

Answer 1

reciprocal translocation

Question 2

mosaic combination of male and female tissue

Answer 2

gynandromorph

Question 3

including the centromere

Answer 3

pericentric

Question 4

excluding the centromere

Answer 4

paracentric

Question 5

having complete sets of chromosomes

Answer 5

euploids

Question 6

having more than two complete sets of chromosomes

Answer 6

polyploidy

Question 7

movement of short DNA elements

Answer 7

transposition

Question 8

lacking one or more chromosomes or having one or more extra chromosomes

Answer 8

aneuploids

Question 9

for the following types of chromosomal arrangements, would it theoretically ever be possible to obtain a perfect reversion of the rearrangement? if so, would such revertants be found only rarely, or would they be relatively common?

a. a deletion of a region including five genes
b. a tandem duplication of a region including five genes
c. a pericentric inversion
d. a Robertsonian translocation
e. a mutation caused by a trasnposable element jumping into a protein coding exon of a gene

Answer 9

a. impossible
b. can occur fairly frequently
c. in most cases there is no mechanism to ensure that the breaks will occur in the same locations as the original breaks that gave rise to the pericentric inversion, so the rate of reversion should be extremely low. One exception to this are inversions that result from intrachromosomal crossing-over between some sequence of DNA that is present at two locations on the same chromosome but in reversed order
d. If the organism with the Robertsonian translocation has already lost the very small reciprocal chromosome generated in the process of translocation then the translocation cannot be restored. If the small reciprocal chromosome still exists, then it is possible that the translocation could revert if it came about through crossing-over between repeated elements
e. For some types of transposable elements, the mechanism that allows the transposable element to jump into the gene can also allow the element to jump out again, often restoring the original DNA sequence of the gene (Fig. 13.23b). In these cases, the mutation will revert fairly frequently

Question 10

Genes a and b are 21 mu apart when mapped in highly inbred strain 1 of corn and 21 mu apart when mapped in highly inbred strain 2. But when the distance is mapped by test crossing the F1 progeny of a cross between strain 1 and 2 the two genes are only 1.5 mu apart. what arrangement of genes a and b and any pontential rearrangement breakpoints could explain these results?

Answer 10

There are 2 possibilities for the inverted region: (i) It includes almost all the region between genes a and b, but does not include the genes themselves, or (ii) the inversion includes both genes and the DNA in between them.

Question 11

common red clover, Trifolium pratense, is a diploid with 14 chromosomes per somatic cell. what would be the somatic chromosome number of:

a. a trisomic variant of this species?
b. a monosomic variant of this species?
b. a triploid variant of this species?
d. a autoteraploid variant?

Answer 11

a. 15
b. 13
c. 21
d. 28

Question 12

The numbers of chromosomes in the somatic cells of several oat varieties (avena species) are: sand outs (avena strigose)-14; slender wild outs (Avena barata) - 28; and cultivated outs (Avena sativa) - 42.

a. what is the basic chromosome number in Avena?
b. what is the policy for each of the different species?
c. what is the number of chromosomes in the gametes produced by each of these oat varieties?
d. what is the n number of chromosomes in each species?

Answer 12

a. The x number in Avena is 7. This represents the number of different chromosomes that make up one complete set.
b. Sand oats are diploid (2x = 14); Slender wild oats are tetraploid (4x = 28); Cultivated wild oats are hexaploid (6x = 42).
c. The number of the chromosomes in the gametes must be half of the number of chromosomes in the somatic cells of that species. Sand oats: 7; slender wild oats: 14; cultivated wild oats: 21.
d. The n number for each species is the number of chromosomes in the gametes and therefore is the same as the answer in part (c).

Question 13

Genomes A,B, and C all have basic chromosome numbers of nine. these genomes were derived originally from plant species that had diverged from each other sufficiently far back in the evolutionary past that the chromosomes from one genome can no longer pair with the chromosomes from any other genome. For plants with the following kinds of euploid chromosome complements, (i) state the number of chromosomes in the organism; (ii) provide terms that describe individual’s genetic makeup as accurately as possible; (iii) state whether or not it is likely that this plant will be fertile, and if s, give the number of chromosomes (n) in the gametes.

a. AABBC
b. BBBB
c. CCC
d. BBCC
e. ABC
f. AABBCC

Answer 13

a. (i) 5x = 45 chromosomes, (ii) allopentaploid, (iii) should be sterile - there are an odd number of chromosomes so there is no way to get an even distribution of chromosomes to the gametes during meiosis.
b. (i) 4x = 36 chromosomes, (ii) autotetraploid, (iii) should be fertile if the chromosomes could pair as bivalents or as quadrivalents.
c. (i) 3x = 27 chromosomes, (ii) autotriploid, (iii) should be sterile because there is an odd number of chromosomes.
d. (i) 4x = 36 chromosomes, (ii) allotetraploid, specifically an amphidiploid, (iii) should be fertile as the chromosomes in the two B genomes can pair with each other as bivalents and the chromosomes in the two D genomes can do the same, n = 18.
e. (i) 3x = 27 chromosomes, (ii) allotriploid, (iii) infertile; the chromosomes cannot pair at all.
f. (i) 6x = 54 chromosomes, (ii) allohexaploid, (iii) should be fertile as each chromosome has a pairing partner of its own type, n = 27.