2) A cell has 40 chromosomes at Gl. a. What is the haploid number of chromosomes

Question

2) A cell has 40 chromosomes at Gl. a. What is the haploid number of chromosomes? b. How many sister chromatids does it have? C. Does the number of sister chromatids change at G2? Why or why not? How many are there? d. After completing mitosis, how many chromosomes are in the daughter cells? This cell then undergoes meiosis. e. How many sister chromatids does it have at prophase I? f. How many chromosomes does it have before anaphase 1? g. How many chromosomes are in the daughter cells after meiosis 1? h. How many sister chromatids are in the daughter cells after meiosis I? i. Is the cell considered diploid or haploid after mciosis P J. Following meiosis II, how many chromosomes would the daughter cells have? K. How many sister chromatids would the daughter cells have? 1. How many cells are produced by one complete cycle of meiosis?

Explanation / Answer

2) A. Haploid means n number of chromosomes. So 2n=40. n=20.

B. When the cell is not dividing, it has 40 chromatids. But, when it goes for division, then it has 40×2=80 chromatids.

C. Yes. The number of Chromatid changes during G2 phase. Synthesis phase occurs between G1 and G2 phase. Where, the cell content gets doubled. So, now it has 40*2 = 80 chromatids. (I mentioned this in the previous question also that during division it gets doubled. Otherwise not.)

D. In mitosis, the mother cell is divided into half and produces two daughter cell. So, mother cell doubled its content during the S phase and now it is divided equally in those daughet cell. So, the daughers will have 2n chromosomes. So, in daughter cell after mitosis there are 40 chromosomes just like their mother cell.

E. So, now a cell has 40 chromosomes and it is going under prophase I. So, there is also a G2 phase just before the prophase I. In G2, the chromatid doubles. So, it has chromatid number 40×2=80

F. It has 40 chromosomes before anaphase I. Because the cells are not divided yet completely in anaphase I.

G. After the end of meiosis I, the chromosome numbers become half. So, each of the daughter cell now has n number chromosome. That is 20.

H. The chromatids are double is number. 20×2=40

I. The cell considered as haploid. As the chromosome number is n = 20.

J. Meiosis II is similar to mitosis. So, daugher cell will have same chromosomes as mother cell. The number will be 20. (As the daughter cell is produced from a cell which has 20 chromosomes . Refer ans of Q. i)

K. They will have 20 chromatids.

L. After meiosis I , 2 daughter cells are produced. After meiosis II, each of those 2 cells produces 2 daughter cells. So, 2×2=4 cells.

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