Question

6. Mutations can occur on the chromosomal level. If pieces of chromosome are missing, the missing DNA is referred to as deletions or deficiencies. If these are large enough, they result in inviable gametes and are not transmitted to the offspring. If pieces of chromosomes are replicated two or more times, the extra DNA is referred to as duplications. These are more likely to be passed to the offspring than deficiencies and often produce dominant phenotypes. If pieces of chromosome change their orientation but stay in the same position on the chromosome, they are referred to as inversions. Pericentric inversions include the centromere. Paracentric inversions do not include that portion of the chromosome where the centromere is located. Translocations are where a piece of chromosome is attached different chromosome. Reciprocal transloc pieces of DNA. If one whole chromosome is missing, the org organisms cannot survive the loss of one chromosome depending on the chromosome in question. Some polyploid organisms can tolerate monosomy for certain chromosomes. If there is one extra chromosome the organism is trisomic. Diploid organisms are more likely to survive trisomy again depending on the chromosome in question. ations are where two nonhomologous chromosomes exchange anism is monosomic. Most diploid

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

B. Also, explain how would you distinguish among pericentric inversions, paracentric inverisons, reciprocal translocations and non reciprocal 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 stock, which would you prefer to use and why?

Answer 1

a)The organism that is heterozygous to the inversion is able to produce only the abnormal chromatids and this occurs when the crossing over occurs within the span of inversion and therefore they produce lower offspring because of lower fertility and organsims that are heterozygous to the translocation also produces less number of offspring because they are semi-fertile and they produce half the number of offspring they usually prooduce and they are also viable.

b) The differences between the paracentric inversion and the pericentric inversion in terms of the meiotic figures is the paracentric inversion involves the centromere in the separation and the pericentric inversion do not have centromere in the meiotic separation.The reciprocal transloction results from the exchange of the segments between the two chromosomes whereas the non-reciprocal translocation are those that have only one way transfer of the chromosome segement to another.

c) The unbalanced chromosome produced by the chromosomal aberrations can be used for the genetic maooing or the linkage of genes.This chromosomal aberrations is simple and convenient in mapping the unknown genes.The chromosomal aberrations produce the deletion,inversion and translocation that is directly allowed for the mapping of the genesto positions on chromosomes.

d) If we were mapping a gene we may use the trisomic stock because the monsomic stock is the one with a single chromosome.In the trisomic tester a new chromosme may be located much easily.