Types of Chromosome Mutations

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Types of Chromosome Mutations Refer to Figure 17-2, Griffiths et al., 2015.

Chromosome Mutations: Changes in Chromosome Structure A B C D E F A C D E F Deletion/Deficiency A B C D E F A B B C D E F Duplication A B C D E F A E D C B F Inversion A B C D E F A B C D J K Translocation G H I J K G H I E F

Origins of Chromosomal Rearrangements Nonallelic Homologous Recombination (NAHR) Refer to Figure 17-19, Griffiths et al., 2015.

Chromosome Mutations Deletion/Deficiency Duplication Inversion A B C D E F A C D E F Deletion/Deficiency A B C D E F A B B C D E F Duplication A B C D E F A E D C B F Inversion A B C D E F A B C D J K Translocation G H I J K G H I E F

pericentric inversion Inversions A B C D E F G H A B F E D C G H pericentric inversion A B C D E F G H A B C D E G F H paracentric inversion A heterozygote for a normal chromosome and an inversion will form an inversion loop during meiosis. The number of recombinant products is reduced in inversion heterozygotes by: 1) elimination of crossing over products within the inversion loop, and 2) inhibition of pairing between homologues in the region of the inversion.

Pairing in paracentric inversion heterozygotes and resulting meiotic products. Anaphase bridge results in random breakage of chromosomal material. 2 of 4 meiotic products are not genetically balanced and will not produce viable gametes.

Pairing in pericentric inversion heterozygotes and resulting meiotic products.

Possible effects of inversion at the molecular level No disruption of any gene. Chromosomal rearrangement is the only result. Disruption of one gene by chromosomal breakage. Disruption of two genes and fusion of those two genes.

Chromosome Mutations Deletion/ Deficiency Duplication Inversion A B C D E F A C D E F Deletion/ Deficiency A B C D E F A B B C D E F Duplication A B C D E F A E D C B F Inversion A B C D E F A B C D J K Translocation G H I J K G H I E F

Translocation In reciprocal translocation, exchange of chromosomal segments between two nonhomologous chromosomes establishes new linkage groups. A B C D E F G H G C D E F A B H In Robertsonian translocation, long arms of two acrocentric chromosomes are combined to form one large chromosome and one small chromosome. If the short metacentric chromosome does not contain essential genetic information, it could be lost without any consequence to viability.

Reciprocal Translocation heterozygotes are semisterile. 50% of gametes are genetically unbalanced. In plants, these gametes are not viable. In animals, zygotes that are formed by these gametes are not viable. Adjacent segregation produces genetically unbalanced gametes. Alternate segregation produces genetically balanced gametes.

Down Syndrome and Translocation Heterozygote Down syndrome is caused by trisomy 21 (3 copies of chromosome 21). 95% of Down syndrome cases are associated with nondisjunction and shows no familial recurrence. The other 5% (familial Down syndrome) is attributed to Robertsonian translocation between chromosome 21 and chromosome 14.