Important Terms

chromosome mutation (p. 000) metacentric chromosome (p. 000) submetacentric chromosome (p. 000) acrocentric chromosome (p. 000) telocentric chromosome (p. 000) chromosome rearrangement (p. 000) aneuploidy (p. 000) polyploidy (p. 000) chromosome duplication (p. 000) tandem duplication (p. 000)

displaced duplication (p. 000) reverse duplication (p. 000) chromosome deletion (p. 000) pseudodominance (p. 000) haploinsufficient gene (p. 000) chromosome inversion (p. 000) paracentric inversion (p. 000) pericentric inversion (p. 000) position effect (p. 000) dicentric chromatid (p. 000) acentric chromatid (p. 000) dicentric bridge (p. 000) translocation (p. 000) nonreciprocal translocation (p. 000)

reciprocal translocation (p. 000) robertsonian translocation (p. 000) alternate segregation (p. 000) adjacent-1 segregation (p. 000) adjacent-2 segregation (p. 000) fragil site (p. 000) nullisomy (p. 000) monosomy (p. 000) trisomy (p. 000) tetrasomy (p. 000) down syndrome (trisomy 21) (p. 000) primary Down syndrome (p. 000)

familial Down syndrome (p. 000) translocation carrier (p. 000) Edward syndrome

(trisomy 18) (p. 000) Patau syndrome (trisomy 13) (p. 000) trisomy 8 (p. 000) uniparental disomy (p. 000) mosaicism (p. 000) gynandromorph (p. 000) autopolyploidy (p. 000) allopolyploidy (p. 000) unbalanced gametes (p.000)

Worked Problems

1. A chromosome has the following segments, where • represents the centromere.


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.)



The types of chromosome mutations are identified by comparing the mutated chromosome with the original, wild-type chromosome.

(a) The mutated chromosome (A B E • F G) is missing segment C_D; so this mutation is a deletion.

(b) The mutated chromosome (A E D C B • F G) has one and only one copy of all the gene segments, but segment

B C D E 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.

(c) The mutated chromosome (ABABCDE^F

G) is longer than normal, and we see that segment A_B has been duplicated. This mutation is a tandem duplication.

(d) The mutated chromosome (A F • E D C B G) is normal length, but the gene order and the location of the centromere have changed; this mutation is therefore a pericentric inversion of region (B C D E • F).

(e) The mutated chromosome (ABCDE EDC

• F G) contains a duplication (C D E) that is also inverted; so this chromosome has undergone a duplication and a paracentric inversion.

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.

(a) Autotriploid for species I

(b) Allotetraploid including species I and II

(c) Monosomic in species I

(d) Trisomic in species II for chromosome M

(e) Tetrasomic in species I for chromosome A

(f) Allotriploid including species I and II

(g) Nullisomic in species II for chromosome N

To work this problem, we should 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.

(a) An autotriploid is 3n, with all the chromosomes coming from a single species; so an autotriploid of species I will have chromosomes AAABBB (3n = 6).

(b) 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; ABMMMNNNOOO).

(c) A monosomic is missing a single chromosome; so a monosomic for species 1 would be 2n — 1 = 4 — 1 = 3. The monosomy might include either of the two chromosome pairs, with chromosomes ABB or AAB.

(d) Trisomy requires an extra chromosome; so a trisomic of species II for chromosome M would be 2n + 1 = 6 + 1 = 7


(e) A tetrasomic has two extra homologous chromosomes; so a tetrasomic of species I for chromosome A would be 2n + 2 = 4 + 2 = 6 (AAAABB).

(f) 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).

(g) A nullisomic is missing both chromosomes of a homologous pair; so a nullisomic of species II for chromosome N would be 2n — 2 = 6 — 2 = 4 (MMOO).

The New Genetics

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