Which one of the following statements is correct for dosage compensation in human?
The body of female is a mosaic of cells, some having paternal X- and others having maternal X-inactivated.
Dosage Compensation in Humans
Dosage compensation is a genetic mechanism that equalizes the expression of genes on the X chromosome between individuals with different numbers of X chromosomes, such as males (XY) and females (XX). In humans and other mammals, this is achieved primarily through X-chromosome inactivation (also known as Lyonization) in females.
X-chromosome Inactivation Explained
In females, one of the two X chromosomes in each somatic cell is randomly inactivated early in embryonic development. This inactivated X chromosome condenses into a compact structure called a Barr body.
- This process ensures that females, who have two copies of X-linked genes, express them at a similar level to males, who have only one copy.
- The choice of which X chromosome (maternal or paternal) to inactivate is generally random in each cell.
- Once a cell undergoes inactivation, all its descendant cells will inactivate the same X chromosome.
Analyzing the Options
Let's examine each statement based on our understanding of dosage compensation in human females:
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X-chromosome inactivation in female occurs in a zygote immediately after fertilization.
This statement is incorrect. X-chromosome inactivation does not happen immediately after fertilization in the zygote. It occurs later, during early embryonic development, after several cell divisions have taken place.
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X-chromosome inactivation is non-random, in some individuals maternal X is inactivated while in others paternal X-chromosome is inactivated.
This statement is generally incorrect for most somatic tissues. While there can be exceptions (e.g., imprinted inactivation of the paternal X in the placenta), X-inactivation in the embryo proper is typically a random process. In different cells within the same individual, either the maternal or the paternal X chromosome is randomly chosen for inactivation.
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Y-chromosome of males is seen as Barr body.
This statement is incorrect. A Barr body is the inactivated X chromosome found in the somatic cells of females and individuals with more than one X chromosome. The Y chromosome does not form a Barr body.
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The body of female is a mosaic of cells, some having paternal X- and others having maternal X-inactivated.
This statement is correct. Due to the random nature of X-chromosome inactivation, different cells in a female's body will have inactivated different X chromosomes. Some cells will have the maternal X active and the paternal X inactivated, while other cells will have the paternal X active and the maternal X inactivated. This makes the female body a genetic mosaic for X-linked genes.
Mosaic Nature of Female Body
The random inactivation of either the maternal or paternal X chromosome in different cells leads to a mosaic pattern of gene expression in females. For X-linked traits, a female might express the allele from her maternal X in some cells and the allele from her paternal X in other cells, depending on which chromosome was inactivated in those cell lineages.
Important Questions from Human genetics
Two strains of mice which are genetically identical except for a single genetic locus or region are said to be:
Interacting genes which are involved in producing continuous variation in phenotypes in a population are known as/constitute
The table given below shows the Lod score values of three different pairs of genes studied for assessing if they are linked pairs:
Gene Pair '1' Gene Pair '2' Gene Pair '3' Lod Score 1 2 3 The following conclusions were made from the data given above:
A. For gene pair 1 the probability of the genes being linked is 10 times more likely than them assorting independently.
B. For gene pair 2, the Lod score 2 indicates that the probability of the genes being linked is twice more likely than assorting independently.
C. The genes of pair 1 and 2, can both be considered as linked, while the genes of pair 3 exhibits independent assortment.
D. The genes of pair 3 can be considered as linked.
Which one of the following options represents statement(s) that is/are correct?
Sampling of 200 persons for their ABO blood group was done from an urban area. The types of blood group observed in the given population are as follows:
A = 60, B = 32, AB = 10 and O = 98
Which of the following gives the correct frequency of blood group determining alleles IA , IB and IO in the given population?
Columns X and Y of the following table list some treatment methods, reagents, and events that are related to human lymphocyte culture, and banding/ karyotyping of human chromosomes.
Column X
Column Y
A.
5% barium hydroxide treatment at 50°C
I.
R-banding
B.
Trypsin treatment
II.
C-banding
C.
Phytohaemagglutinin
III.
Mitotic stimulation
D.
Phosphate buffer treatment at 80°C
IV.
Nucleolar Organizer Regions (NOR)
E.
Silver Staining
v.
G-banding
Which one of the following options represents all correct matches between Column X and Column Y?
