172
Problem 1
A chromosome has the following segments, where • represents the centromere:
ABCDE•FG
What types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.)
ABE•FG
AEDCB•FG
ABABCDE•FG
AF•EDCBG
ABCDEEDC•FG
Solution Strategy
What information is required in your answer to the problem?
The types of chromosome mutations that would lead to the chromosome shown.
What information is provided to solve the problem?
The original gene segments found on the chromosome.
The altered gene segments that occur after the mutations.
For help with this problem, review:
Section 6.2.
173
Solution Steps
The mutated chromosome (ABE•FG) is missing segment CD, so this mutation is a deletion.
The mutated chromosome (AEDCB•FG) has one and only one copy of all the gene segments, but segment BCDE has been inverted 180 degrees. Because the centromere has not changed location and is not in the inverted region, this chromosome mutation is a paracentric inversion.
The mutated chromosome (ABABCDE•FG) is longer than normal, and we see that segment AB has been duplicated. This mutation is a tandem duplication.
The mutated chromosome (AF•EDCBG) is normal length, but the gene order and the location of the centromere have changed; this mutation is therefore a pericentric inversion of region (BCDE•F).
The mutated chromosome (ABCDEEDC•FG) contains a duplication (CDE) that is also inverted; so this chromosome has undergone a duplication and a paracentric inversion.
Problem 2
Species I is diploid (2n = 4) with chromosomes AABB; related species II is diploid (2n = 6) with chromosomes MMNNOO. Give the chromosomes that would be found in individuals with the following chromosome mutations.
Autotriploidy in species I
Allotetraploidy including species I and II
Monosomy in species I
Trisomy in species II for chromosome M
Tetrasomy in species I for chromosome A
Allotriploidy including species I and II
Nullisomy in species II for chromosome N
Solution Strategy
What information is required in your answer to the problem?
The chromosomes that will be found in individuals with each type of mutation.
What information is provided to solve the problem?
Species I has chromosomes AABB.
Species II is diploid with 2n = 6.
Species II has chromosomes MMNNOO.
Species I is diploid with 2n = 4.
For help with this problem, review:
Sections 6.3 and 6.4.
Solution Steps
Hint: First determine the haploid genome complement for each species. For species I, n = 2 with chromosomes AB and, for species II, n = 3 with chromosomes MNO.
An autotriploid is 3n, with all the chromosomes coming from a single species; so an autotriploid of species I would have chromosomes AAABBB (3n = 6).
An allotetraploid is 4n, with the chromosomes coming from more than one species. An allotetraploid could consist of 2n from species I and 2n from species II, giving the allotetraploid (4n = 2 + 2 + 3 + 3 = 10) chromosomes AABBMMNNOO. An allotetraploid could also possess 3n from species I and 1n from species II (4n = 2 + 2 + 2 + 3 = 9; AAABBBMNO) or 1n from species I and 3n from species II (4n = 2 + 3 + 3 + 3 = 11; ABMMMNNNOOO).
A monosomic individual is missing a single chromosome; so monosomy in species I would result in 2n − 1 = 4 − 1 = 3. The monosomy might include either of the two chromosome pairs, giving chromosomes ABB or AAB.
Trisomy requires an extra chromosome; so trisomy in species II for chromosome M would result in 2n + 1 = 6 + 1 = 7 (MMMNNOO).
A tetrasomic individual has two extra homologous chromosomes; so tetrasomy in species I for chromosome A would result in 2n + 2 = 4 + 2 = 6 (AAAABB).
An allotriploid is 3n with the chromosomes coming from two different species; so an allotriploid could be 3n = 2 + 2 + 3 = 7 (AABBMNO) or 3n = 2 + 3 + 3 = 8 (ABMMNNOO).
A nullisomic individual is missing both chromosomes of a homologous pair; so a nullisomy in species II for chromosome N would result in 2n − 2 = 6 − 2 = 4 (MMOO).