Question

Normal gene order for a particular chromosome is ABC*DEF (where * is the centromere). An inversion changed the gene order to AD*CBEF. If an individual is heterozygous for the inversion (has one normal chromosome, and one with the inversion), show how the two chromosomes will pair in meiosis. Then show the chromosomes that will result if crossing over occurs in the inversion. Please draw a picture

Answer 1

Inersion is a type of muation in which the chromosome breaks at two end within the segment and changes its orientation and get inserted into the same segment. There ae two types of inversion Para centric inversion and Pericentric inversion. In Paracentric inversion there in no involvement of centromere whereas pericentric inversion centromere included in the inverted segment. There is not net loss or gain of genetic material in this type of mutation.

Here the given sequence of gene in a chromosome is

normal gene: ABC*DEF where * is centromere

Inverted gene: AD*CBEF There is inversion across the centromere hence Pericentric inversion.

Since the person is heterozygous for the inversion he wil contain one iverted chromosome and one normal chromosome . During miosis homologus chromosome pairs, pairing of inverted and normal chromosome produces a inversion loop.Cross over gives viable and inviable gamtes. If a single crossing over occurs there can be 4 different types of products.

1. No cross over in the first chromosome, hence has normal order of gene mainatined. resulting in a viable gamete.

2.The second chromosome cross over occurs resulting in a gamete were there will be loss of genes E, F and duplication of gene A. due to the deletion and duplication it is not viable.

3. Third chromosome not involved in cross over. Same genes as original hence viable.

4. Fourth chromosome duplication of gene E and F and absence of gene A. It is non viable due to deletion and duplication.