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mitotic neutrophilic somatic nuclear methylation sex Barr embryonic nucleus female buccal |
………. of the DNA
………. cells
………. chromatin
………. development
………. epithelium
………. body
………. leukocytes
………. chromosome
………. centre
………. activity
………. membrane
8Complete the sentences below using logical links from the box. Use each word or phrase once only.
secondly while at the same time firstly while thus in the case mostly but which only nor also |
This topic is about sex–chromatin which is ………. called “Barr body”. It is the substance of genetically inactivated X-chromosome detected in normal conditions ………. in somatic (diploid) cells in females. In granular neutrophilic leukocytes “sex–chromatin” appears as a “drumstick”. ………. the number of X–chromosomes is equal to the number of bodies of sex-chromatin plus one. ………. in the cells of different tissues the recurrence of “sex chromatin” is different. ………., 80 – 90% of neuron nuclei contain “sex chromatin”, ………. only 20 – 40% of cell nuclei of the buccal epithelium contain it. “Sex chromatin” is localized in the nucleus, ………. attached to the nuclear membrane by thin filaments. ………. when “sex chromatin” is attached to the nuclear membrane, it has a triangle shape with the apex directed towards the nucleus centre. All organisms with two X-chromosomes in their karyotypes contain only one body of “sex- chromatin”, ………. in the case of trisomy of X – chromosome the nucleus contains two bodies of “sex- chromatin”.
There is a reverse correlation between the mitotic activity of the cell population and the frequency of sex–chromatin occurrence.
On the fifth and sixth days of embryonic development in a female organism inactivation of one of the two “X–chromosomes” takes place. The mechanism of this phenomenon is conditioned by methylation of the DNA in the inactivated chromosome. There is a special site Xq27.3 (CpG islet) containing multiple cytosine-guanine repeats ………. can be methylated. They are methylated in the Barr body ………. are not methylated in the second (active) female Х-chromosome, ………. they are methylated in male X–chromosome.
Дата публикования: 2014-11-03; Прочитано: 621 | Нарушение авторского права страницы | Мы поможем в написании вашей работы!