Question

Genetics Chapter 4:

A color-blind woman with Turner syndrome has a father who is color-blind. Given that the gene for the color-blind condition is recessive and X-linked, provide a likely explanation (name and define the phenomenon involved) for the origin of the color-blind and cytogenetic conditions in the woman.

Answer 1

The phenomenon which leads to a color-blind woman with Turner syndrome from a color-blind father is called non-disjunction.  Non-disjunction is a failure of segregation of chromosomes during cell division which leads to development of errors in chromosome number, such as monosomy X i.e N-1 where N is the chromosome number (Turner syndrome) or trisomy 21 (Down syndrome).

In the given conditions, the father is a color-blind which passes the mutant allele to his daughter, thus giving the color-blindness to her. Along with this character, the daughter has Turner syndrome meas 45,XO condition i.e partial deletion of X chromosome. This can only be explained by the fact that the non-disjunction must have occurred in the mother because the fertilization happened between an X-bearing sperm, which carried the mutant allele for color blindness, and a nullo-X egg.