Question

In mammals, each inactivated X chromosome forms a darkly staining body known as a _____ body.

a. Lyon
b. Bridges
c. Morgan
d. Z
e. Barr

Answer 1

In mammals, each inactivated X chromosome forms a darkly staining body known as a Barr body, which is a result of the X inactivation process that compensates for the double genetic dose of X chromosomes in females.

Step-by-step explanation:

In mammals, each inactivated X chromosome forms a darkly staining body known as a Barr body. The process of X inactivation enables female mammals to compensate for their double genetic dose of the X chromosome. This random inactivation occurs early in development when the embryonic cells are few and causes the X chromosome to condense into a dormant structure.

As a result, cells descended from the original cell with the inactivated X chromosome will also have the same inactive X. This phenomenon is observable in certain traits such as the coat color variegation seen in tortoiseshell cats, where females express different coat colors in different body regions depending on which X chromosome was inactivated.

Answer 2

The darkly staining body formed by each inactivated X chromosome in mammals is known as a Barr body. This is a part of the X inactivation process, which helps female mammals to balance the genetic dosage of the X chromosome. Option e. Barr is the correct answer.

Step-by-step explanation:

In mammals, each inactivated X chromosome forms a darkly staining body known as a Barr body. This process, referred to as X inactivation, occurs early in the development of female mammalian embryos. As the embryos consist of just a few thousand cells, one of the X chromosomes in each cell is randomly inactivated by condensing into a quiescent structure named a Barr body. Once an X chromosome is inactivated, all the cells descended from that original cell will also have the same inactive X chromosome. This phenomenon allows females to compensate for their double genetic dose of X chromosome.

In cases like "tortoiseshell" cats, the X inactivation leads to color variegation, where the regions of different colors represent the inactivation of different X chromosomes occurring in different embryonic cell progenitors. Humans and other mammals can function normally with varying numbers of X chromosomes, partly due to this X inactivation process. Trisomies and monosomies typically cause severe consequences in autosomes, but variations in sex chromosomes, thanks to mechanisms like a Barr body formation, often have milder effects.

The correct option for the question regarding the darkly staining body formed by each inactivated X chromosome in mammals is e. Barr.