PHED-4547EL Lecture Notes - Lecture 3: Mary F. Lyon, X-Inactivation, Chromatin

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Chapter 3 genes, dna, chromosomes, and cell division. Female carrier of recessive x-linked trait is normal; effect of defective allele offset by normal allele on other x chromosome. Male carrier of recessive x-linked trait; defective x chromosome functions like a dominant gene. X activation or lyonization: only one of the two x chromosomes in females is genetically active; one is inactivated around 16th day of embryonic development; theorized by mary. Barr body or sex chromatin body: inactive x chromosome. X activation occurs so females with two x chromosomes do not have twice as many x chromosome gene products as males. Choice of which x chromosome will be inactivated is random; when activated, it remains inactive throughout the lifetime of the cell. Study of composition and abnormalities in chromosomes in terms of number and structure. Methods: use human blood as source of cells and then culture, lymphocytes induced to undergo mitotic division.

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