Q 12. - Biology

Question

Abnormalities in the number of X chromosomes tends to have milder phenotypic effects than the same abnormalities in autosomes because of _______

a. deletions 

b. nonhomologous recombination 

c. synapsis 

d. X inactivation  

Step-by-Step Solution

Answer

The correct option is (d).

Step 1. Introduction

Variations in the number of sex chromosomes are connected with relatively mild effects rather than a gain or loss of autosomes. This is due in part to a molecular process known as X inactivation.

Step 2. Explanation of correct option

X-chromosome inactivation happens at random in female cells during development for one of the two X chromosomes. When RNA transcribed from the X gene on the X chromosome from which it is expressed spreads to coat the entire X chromosome, inactivation occurs.

Step 3. Explanation of Incorrect Options

Deletion- The term "deletion" simply refers to a missing or "deleted" portion of a chromosome. Many different genes can be found on a relatively short portion of a chromosome. Because part of the "instructions" are absent when genes are lacking, there may be errors in a baby's development.

Non-homologous recombination- Nonhomologous recombination (NHR) is a significant route for somatic cell DNA repair of chromosomal double-strand breaks.

Synapsis- The genes on the chromatids of homologous chromosomes are properly aligned with each other in synapsis. Crossing over, or the exchange of chromosomal segments between non-sister homologous chromatids is supported by the synaptonemal complex.