Question

What are inversion heterozygotes? How can meiotic pairing occur in these organisms? What will be the consequence?

Short answer

Answer: An inversion heterozygote is an organism with two homologous chromosomes, where one has a reversed segment (inversion) and the other has the normal gene arrangement. During meiotic pairing, an inversion loop is formed to allow the proper alignment of homologous genes. However, if recombination occurs within the inversion region, it can result in unbalanced gametes that may cause reduced fertility or offspring viability due to genetic imbalances.

Step-by-step solution

Definition of Inversion Heterozygotes

Inversion heterozygotes are organisms with two homologous chromosomes, one of which has a reversed segment (inversion), while the other has the normal gene arrangement. The region where the order of genes is reversed is called the inversion region.

Meiotic Pairing in Inversion Heterozygotes – Formation of Inversion Loop

Meiotic pairing occurs when homologous chromosomes align and synapse (pair) during prophase I of meiosis. In inversion heterozygotes, due to the presence of an inversion region, a characteristic loop must be formed so that homologous genes can align and pair with each other. This loop is called the inversion loop.

Recombination and Crossing Over in Inversion Heterozygotes

While meiotic pairing is occurring, recombination and crossing over (exchange of genetic material) can take place between non-sister chromatids of homologous chromosomes. In inversion heterozygotes, crossing over within the inversion loop can lead to problems during chromosome segregation in anaphase of meiosis I if the recombination event involves only one of the two homologous chromosomes' inverted regions. This will result in the formation of unbalanced gametes which carry duplications and deletions of certain genes.

Consequences of Meiotic Pairing in Inversion Heterozygotes - Reduced Fertility or Offspring Viability

When unbalanced gametes are produced due to recombination within the inversion region, it can result in reduced fertility or offspring viability. This is because the offspring may possess missing or extra copies of certain genes, leading to various developmental or functional abnormalities, depending on the specific genes involved. In conclusion, inversion heterozygotes are organisms with an inverted region in one of their homologous chromosomes. The meiotic pairing in these organisms involves the formation of an inversion loop, allowing the pairing of homologous genes despite the inversion. However, if recombination occurs within the inversion region, it can lead to unbalanced gametes that may cause reduced fertility or offspring viability due to genetic imbalances.