a. Organisms heterozygous for inversions and translocations are viable and able

Question

a. Organisms heterozygous for inversions and translocations are viable and able to produce progeny, but usually in reduced numbers. Explain why this is so in general terms.

b. Also, explain how you would distinguish among pericentric inversions, paracentric inversions, reciprocal translocations, and nonreciprocal translocations as sources of semi-sterility. You need to consider meiotic figures.

c. How can these chromosome aberrations be used to map genes to chromosomes or linkage groups? You may use a two-point mapping system as an example.

d. If you were mapping a gene to a chromosome group with monosomic or trisomic stocks, which would you prefer to use and why?

Explanation / Answer

a. Inversion heterozygotes are the organisms whose homologous chromosomes have different structural organisation. The large heterozygous inversion will result in greater numbers of genes that are duplicated or deleted when crossing over occurs. The significant reduction or absence of progeny with recombinant chromosomes is due to crossover suppression.

An organism with chromosome translocation in which chromosome pair consists of one normal chromosome and a homolog carrying translocation. The reduced fertility, is common result of adjacent segregation during meiosis in balanced translocation heterozygoyes.

b.

Paracentric inversion Pericentric inversion It does not occur in centromere. It occurs in centromere. Crossing over occurs within the loop, which causes the cells to die during meiosis. Recombination occurs inside the loop. Dicentric and acentric bridges are formed . Deletion and duplication can occur during cross over.

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