Title Meiosis in Lily’s anther.
Introduction Meiosis is a singularly important biological event that not only maintains a constant chromosome number for most species of plants or animals, but also provides a means of genetic variability because of ‘crossing over’ and the subsequent exchange of genetic materials. Meiosis reduces the chromosome number by half during the formation of gametes in animals and spores in plants. This process involves two successive nuclear divisions that produce four haploid cells. Meiosis I is the reduction division. It is this first division that reduces the chromosome number from diploid to haploid and separates the homologous pairs. Meiosis I accounts for approximately 90% of the time a cell spends in the entire process. Meiosis II, the second division, separates the sister chromatids. The result is four haploid gametes. When haploid gametes unite during fertilization, the resulting zygote is diploid, having received one chromosome of each pair from each parent. Meiosis takes a good deal of time, and differs from species to species--in human males, the entire process lasts 24 days. In lilies, li lies, it takes seven days. Mitotic cell division produces new cells genetically identical to the parent cell. Meiosis increases genetic variation in the population. Each diploid cell undergoes meiosis that can produce 2n different chromosomal combinations, where n i s the haploid number. In humans the number is 223 which are more than eight million different combinations. In addition, the potential variation is even greater because, during meiosis I, each pair of chromosomes (homologous chromosomes) comes together in a process known as synapsis. Chromatids of homologous chromosomes chromosomes may exchange parts in a process called crossing over. The relative distance between two genes on a given chromosome can be estimated by calculating the percentage of crossing over that takes place between them.
Objective
1. Observe and identify the stage of meiosis in Lily’s anther. 2. Observe and identify the stage of meiosis from the given slide.
Material Microscope, Slide of Lilium second division, Slide of cross-section of ovary, second division.
Procedure 1.
Slide of Lilium second division and Slide of cross-section of ovary second division was observed by microscope.
2. The stage of meiosis process was recorded.
Observation Meiosis I Observed Stage Prophase I
Theory Stage
Description Each duplicated chromosomes is in threadlike form but start to condense. It pairs with its homologous and 2 typically swap segments. The swapping called crossing over. Some of microtubules of a newly forming spindle become attached to each chromosome’s centromere.
Metaphase I
As in mitosis, motor proteins attached to microtubules move the chromosomes and move the spindle poles apart. They thug the chromosome into position midway between the spindle poles. Thus, the spindle becomes fully formed, owing to dynamic interaction among the motor proteins, microtubules and chromosomes themselves.
Anaphase I
Microtubules extending from the poles and overlapping at the spindle equator lengthen and push the poles apart. Other microtubules extending from the poles to the chromosomes shorten, thereby pulling each other away from its homologous partner. This motions move the homologous partners to opposite poles.
Telophase I
The cytoplasm of the cell divides at some point. There are now two haploid cells (n). Each cell has one of each type of chromosomes that was present in the parent (2n) cell. They are still at duplicate stage.
Meiosis II Observed Stage Prophase II
Theory Stage
Description Microtubules have already moved one member of the centrioles pair to the opposite pole of the spindle in each of the two daughter cells. Now the prophase II, microtubules attached to the chromosomes and the motor protein drive the movement of chromosome towards the spindle equator.
Metaphase II
In each daughter cell, interactions among motor proteins, spindle microtubules, and each duplicated chromosomes have move all of the chromosomes so that they are positioned at the spindle equator midway between the two poles.
Anaphase II
The attachment between the two chromatids of each chromosomes breaks. Each of former sister chromatids is now a chromosomes in its own eight. Motor proteins drive the movement of the newly separated chromosomes to opposite poles of the spindle.
Telophase II
By the time telophase II is over, there will be four daughter nuclei. When cytoplasmic division is completed, each new, daughter’s nuclei will have
a haploid chromosome number (n). All of the chromosome will now be in the unduplicated site.
Discussion Meiosis is the process that occurs for reproduction. Such as meiosis occur at Lily anther. But there is another part that we can find the meiosis process is Lily’s ovary. Meiosis reduces
the number of chromosome sets from diploid to haploid. Meiosis, like mitosis, s preceded by the replication of chromosomes. However, this single replication is followed by not one but two consecutive cell divisions, called meiosis I and meiosis II. These two divisions result in four daughter cells, each with only half as many chromosomes as the parent cell. To identify the meiotic division that occurs in the Lili um anther is meiosis process is not starting with interphase but it start with prophase and it has 4 daughter nuclei with 2 chromosomes. The significance of meiotic process in organism is to contribute genetic variation in which during the metaphase I the chromosome may line up at equator in any number of ways. The differences between mitotic and meiotic process that occur in Lily are in mitosis only single division of mother cell that produce 2 daughters cell, but in meiotic two division of mother cell that produce 4 daughters cell. Then, a mitotic mother cell can be haploid or diploid, but in meiotic mother cell only in haploid. In mitosis, there is no pairing chromosome, while in meiosis, during prophase I, it completed pairing of all homologous chromosomes.
Conclusion For meiosis II, the process started with prophase II then it continues with metaphase II, anaphase II and telophase II. At the end of the process, it produces 4 daughter nuclei with two chromosomes.
References http://biology.about.com/library/weekly/aa101900a.html
BIOLOGY, EIGHT EDITION, CAMPBELL.REECE.
