Question

1. Some traits are not transmitted via Mendelian inheritance. Describe three forms of inheritance that do not follow Mendelian inheritance or laws. Hint: These are alternative to dominance and recessivness.

Answer 1

Nonmenedilian inheritance is referred to inheritance of traitsthat do not follow segregation according to Mendel's laws. These include mechanisms such as extranuclear inheritance, gene conversion, infectious heredity and mosaicism. Extranuclear inheritance is also known as cytoplasmic inheritance in which the traits inherited from DNA other than nuclear DNA such as chloroplast or mitochondrial DNA. This cytoplasmic inheritance results in varying proportion of phenotypic ratios. Cytoplasmic inheritance was discovered by Carl Correns in Mirabilis jalapa. In this plant, the leaf color was dependent only on the genotype of the maternal parent.

Gene conversion is another nonmendelian inheritance mechanism arises during DNA repair through DNA recombination. During this mechanism, DNA sequence information is transferred from one DNA helix to another DNA helix resulting in sequence alteration. This may occur due to mismatch repair between the strands of DNA that are derived from different parents. This mostly observed in fungal crosses resulting in different fungal phenotypes.

The presence of cells having different genetic composition than other cells is called mosaicism. The differences in genetic composition are caused due to mutations occurring in different tissues and at different periods of development. The mutation in non-gamete cells or tissues are somatic. Germline mutations occur in the egg or sperm cells and are inherited to offspring. Mutations that occur early on in development will affect a greater number of cells and can result in phenotype mosaicism. Mosaicism is also results from a phenomenon known as X-inactivation and is observed in female calico cats.