Question

Identical, or monozygotic, twins develop from a single egg fertilized by a single sperm. Monozygotic twins are genetically identical because they originate from a single zygote that split into two. Caroline Lost and her colleagues examined nine measures of social, behavioral, and cognitive ability in 1000 pairs of both male and female identical twins. Their study found that pairs of male twins tended to be more alike in their prosocial behavior, peer problems, and verbal ability scores than pairs of female twins. Which of the following choices explains this observation? s on the X and Y chromosomes in the brains of males results Interacting g in identical twins with more similar behaviors Identical male twins express the same X-linked alleles in their neural cells because males undergo random X-inactivation Male twins have similar expression levels of X-linked genes, because the Y chromosome silences expression of X chromosome genes Q Females are mosaic for the expression of heterozygous X-inked loci because females undergo random X-inactivation

Answer 1

Answer:

The correct answer is "Females are mosaic for the expression of heterozygous X-inked loci because females undergo random X-inactivation".

Explanation:

This study reports that pairs of male twins tended to be more alike in their prosocial behavior, peer problems, and verbal ability scores than pairs of female twins. This is explained by the process of random X-inactivation in pairs of female twins. Random X-inactivation is the transcriptional silencing of one X chromosome in female cells during its development. This results in pairs of female twins being mosaic for the expression of heterozygous X-inked, making female twins actually not identical in its phenotype.