1. The presence and association of the sex ch romatin with the number of X chrom
ID: 212767 • Letter: 1
Question
1. The presence and association of the sex ch romatin with the number of X chromosomes and its lado association with the Y chromosome has some genetic consequences. This usually results in some anomalouis chromosome complements with distinct numbers of Barr Bodies. vii) What is the Lyons Hypothesis? vii) What are Barr Bodies? i) Briefly discuss the genetic consequence and importance of X chromosome inactivation Briefly disuss the importance of considering ethical issues associated with gene therapy and genctie screening 2.Explanation / Answer
Lyon's Hypothesis- The hypothesis, named after Mary Lyon who stated it, states that only one of the two X chromosomes in the homogametic sex is functional while the other condenses and is inactivated. The X inactivated in some cells would be that from the father, in other cells it would be that from the mother. This is also termed as dosage compensation where inactivation of all but one X chromosome in cells with more than one X chromosome takes place.
Barr Bodies- The Barr body, also sometimes called the sex chromatin, is the inactive X chromosome in female somatic cells. In all of the female somatic cells, which don’t take part in sexual reproduction, one of the X chromosomes is active, and the other is inactivated in a process called lyonization, becoming the Barr body.
Genetic consequence and importance of X chromosome inactivation- The X chromosome is one of the two sex chromosomes in humans (the other is the Y chromosome). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The X chromosome spans about 155 million DNA building blocks (base pairs) and represents approximately 5 percent of the total DNA in cells. Males have one X and one Y chromosome , while females have two X chromosomes resulting in a potentially toxic double dose of X-linked genes. X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. A classic example of X-inactivation is seen in cats. If a female cat is heterozygous for black and tan alleles of a coat color gene found on the X, she will inactivate her two Xs (and thus, the two alleles of the coat color gene) at random in different cells during development. The result is a tortoiseshell coat pattern, made up of alternating patches of black and tan fur. The black patches come from groups of cells in which the X with the black allele is active, while the tan patches come from cells in which the X with the tan allele is active.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.