Question

Пожалуйста !!!! срочно 4. Установите последовательность процессов, происходящих в ходе мейоза. 1) расположение пар гомологичных хромосом в экваториальной плоскости2) конъюгация, кроссинговер гомологичных хромосом3) расположение в плоскости экватора и расхождение сестринских хромосом4) образование четырёх гаплоидных ядер5) расхождение гомологичных хромосом5. Общая масса всех молекул ДНК в46 хромосомах одной соматической клетки человека составляет около 6·10 −9 мг. Определите, чему равна масса всех молекул ДНК в ядре при овогенезе перед началом мейоза, в анафазе мейоза I и мейоза II. Объясните полученные результаты.

Answer 1

4. 2,1,5,3,4
5. Перед началом мейоза хромосомный набор 2n4c, масса всех молекул ДНК в ядре 6*10-9 мг*2= 12*10-9мг. Так как в синтетическом периоде (S-период) интерфазы клеточного цикла происходит репликация ДНК,но количество хромосом остается прежним.
В анафазе I мейоза хромосомный набор 2n4c, масса всех молекул ДНК ядре 12*10-9мг. Так как в анафазе I мейоза происходит расхождение к полюсам клетки гомологичных двухроматидных хромосом.
В анафазе II мейоза хромосомный набор 2n2c 12*10-9мг:2= 6*10-9 мг. Так как в анафазе II мейоза к полюсам клетки расходятся хроматиды негомологичных хромосом, которые становятся самостоятельными однохроматидными хромосомами.

Answer 2

Sequence of Processes in Meiosis:

The sequence of processes in meiosis can be summarized as follows:

1. Pairing of Homologous Chromosomes in the Equatorial Plane: During prophase I of meiosis, homologous chromosomes come together and pair up in a process called synapsis. This pairing occurs in the equatorial plane of the cell [[1]].

2. Conjugation and Crossing Over of Homologous Chromosomes: During prophase I, homologous chromosomes may exchange genetic material through a process called crossing over. This results in the recombination of genetic material between the homologous chromosomes, increasing genetic diversity [[2]].

3. Alignment in the Equatorial Plane and Separation of Sister Chromatids: During metaphase I, the paired homologous chromosomes align along the equatorial plane of the cell. The homologous chromosomes then separate, with one chromosome from each pair going to each daughter cell. This separation is known as disjunction [[3]].

4. Formation of Four Haploid Nuclei: After the separation of homologous chromosomes, the cell undergoes cytokinesis, resulting in the formation of two daughter cells. Each daughter cell contains half the number of chromosomes as the parent cell, and each chromosome consists of two sister chromatids. These daughter cells then undergo a second round of division, called meiosis II, resulting in the formation of four haploid nuclei, each with a single set of chromosomes [[4]].

5. Separation of Homologous Chromosomes: During anaphase I of meiosis, the homologous chromosomes separate and move to opposite poles of the cell. This ensures that each daughter cell receives one chromosome from each homologous pair [[5]].

Total Mass of DNA in Different Stages of Meiosis:

The total mass of all DNA molecules in the 46 chromosomes of a somatic cell of a human is approximately 6 x 10^-9 mg [[6]].

- Before the Start of Meiosis: Before the start of meiosis, during the oogenesis process, the DNA content in the nucleus is doubled through DNA replication. Therefore, the mass of all DNA molecules in the nucleus remains the same as in a somatic cell, which is approximately 6 x 10^-9 mg.

- During Meiosis I (Anaphase I): During anaphase I of meiosis, the homologous chromosomes separate and move to opposite poles of the cell. At this stage, the DNA content is halved, as each daughter cell receives only one chromosome from each homologous pair. Therefore, the mass of all DNA molecules in the nucleus is reduced to approximately 3 x 10^-9 mg.

- During Meiosis II (Anaphase II): During anaphase II of meiosis, the sister chromatids separate and move to opposite poles of the cell. At this stage, the DNA content is further halved, as each daughter cell receives only one chromatid from each chromosome. Therefore, the mass of all DNA molecules in the nucleus is reduced to approximately 1.5 x 10^-9 mg.

The reduction in DNA mass during meiosis is due to the separation and distribution of genetic material into different daughter cells, resulting in the formation of haploid nuclei.

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