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2006-10-23 17:18:19 · 10 answers · asked by Miss M 4 in Science & Mathematics Biology

10 answers

Specialized germ cells, which are also called gametes. Types of gametes include eggs (or ova), sperm (or spermatozoon), and pollen grain!

2006-10-23 17:19:34 · answer #1 · answered by Doctor Why 7 · 0 1

meiosis is meant for gamete productions...
it produces sperms in males and egg cells in females

and microspores n megaspores in plants....


Meiosis

Meiosis produces daughter cells that have one half the number of chromosomes as the parent cell.

2N -------> N

Meiosis enables organisms to reproduce sexually. Gametes (sperm and eggs) are haploid.

Meiosis is necessary in sexually-reproducing organisms because the fusion of two gametes (fertilization) doubles the number of chromosomes.

Meiosis involves two divisions producing a total of four daughter cells.



Meiosis comprises two successive nuclear divisions with only one round of DNA replication.
Four stages can be described for each nuclear division.

* Interphase: Before meiosis begins, genetic material is duplicated.
* First division of meiosis
o Prophase 1: Duplicated chromatin condenses. Each chromosome consists of two, closely associated sister chromatids. Crossing-over can occur during the latter part of this stage.
o Metaphase 1: Homologous chromosomes align at the equatorial plate.
o Anaphase 1: Homologous pairs separate with sister chromatids remaining together.
o Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.

* Second division of meiosis: Gamete formation
o Prophase 2: DNA does not replicate.
o Metaphase 2: Chromosomes align at the equatorial plate.
o Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole.
o Telophase 2: Cell division is complete. Four haploid daughter cells are obtained.

One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different.

Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes.

2006-10-24 00:29:20 · answer #2 · answered by vimal.N 2 · 1 1

In biology, meiosis is the process that allows one diploid cell to divide in a special way to generate haploid cells in eukaryotes. The word "meiosis" comes from the Greek meioun, meaning "to make smaller," since it results in a reduction in chromosome number.

Meiosis is essential for sexual reproduction. It therefore occurs in most eukaryotes, including single-celled organisms. A few eukaryotes, notably the Bdelloid rotifers, have lost the ability to carry out meiosis and acquired the ability to reproduce by parthenogenesis. Meiosis does not occur in archaea or prokaryotes, which reproduce by asexual cell division processes.

During meiosis, the genome of a diploid germ cell, which is composed of long segments of DNA called chromosomes, undergoes DNA replication followed by two rounds of division, resulting in haploid cells called gametes. Each gamete contains one complete set of chromosomes, or half of the genetic content of the original cell. These resultant haploid cells can fuse with other haploid cells of the opposite gender or mating type during fertilization to create a new diploid cell, or zygote. Thus, the division mechanism of meiosis is a reciprocal process to the joining of two genomes that occurs at fertilization. Because the chromosomes of each parent undergo genetic recombination during meiosis, each gamete, and thus each zygote, will have a unique genetic blueprint encoded in its DNA. In other words, meiosis is the process that produces genetic variation.

Biochemically, meiosis uses some of the same mechanisms employed during mitosis to accomplish the redistribution of chromosomes. There are several features unique to meiosis, most importantly the pairing and recombination between homologous chromosomes, which enable them to separate from each other.

Occurrence of meiosis in eukaryotic life cycles
Meiosis occurs in all eukaryotic life cycles involving sexual reproduction, comprising of the constant cyclical process of meiosis and fertilization. This takes place alongside normal mitotic cell division. In multicellular organisms, there is an intermediary step between the diploid and haploid transition where the organism grows. The organism will then produce the germ cells that continue in the life cycle. The rest of the cells, called somatic cells, function within the organism and will die with it.

The organism phase of the life cycle can occur between the haploid to diploid transition or the diploid to haploid transition. Some species are diploid, grown from a diploid cell called the zygote. Others are haploid instead, spawned by the proliferation and differentiation of a single haploid cell called the gamete. Humans, for example, are diploid creatures. Human stem cells undergo meiosis to create haploid gametes, which are sperm cells for males or ova for females. These gametes then fertilize in the uterus of the female, producing a diploid zygote. The zygote undergoes progressive stages of mitosis and differentiation to create an embryo, the early stage of human life.

There are three types of life cycles that utilise sexual reproduction, differentiated by the location of the organisms stage.

In the gametic life cycle, of which humans are a part, the living organism is diploid in nature. Here, we will generalize the example of human reproduction stated previously. The organism's diploid germ-line stem cells undergo meiosis to create haploid gametes, which fertilize to form the zygote. The diploid zygote undergoes repeated cellular division by mitosis to grow into the organism. Mitosis is a related process to meiosis that creates two cells that are genetically identical to the parent cell. The general principle is that mitosis creates somatic cells and meiosis creates germ cells.

In the zygotic life cycle, the living organism is haploid. Two organisms of opposing gender contribute their haploid germ cells to form a diploid zygote. The zygote undergoes meiosis immediately, creating four haploid cells. These cells undergo mitosis to create the organism. Many fungi and many protozoa are members of the zygotic life cycle.

Finally, in the sporic life cycle, the living organism alternates between haploid and diploid states. Consequently, this cycle is also known as the alternation of generations. The diploid organism's germ-line cells undergo meiosis to produce gametes. The gametes proliferate by mitosis, growing into a haploid organism. The haploid organism's germ cells then combine with another haploid organism's cells, creating the zygote. The zygote undergoes repeated mitosis and differentiation to become the diploid organism again. The sporic life cycle can be considered a fusion of the gametic and zygotic life cycles, and indeed its diagram supports this conclusion.

You could get more information from the link below...

2006-10-24 07:55:17 · answer #3 · answered by catzpaw 6 · 0 1

Naughty sticky cells. Now go to your room ! Good Luck ! :)

2006-10-24 00:20:30 · answer #4 · answered by tysavage2001 6 · 0 2

reproductive cells.

2006-10-24 21:52:43 · answer #5 · answered by moosa 5 · 0 0

gamet cells, such as spermatozoon & ovum.

they r haploids

2006-10-24 04:37:05 · answer #6 · answered by Papilio paris 5 · 0 1

The sex cells, oocytes and spermatozoa

2006-10-24 00:19:46 · answer #7 · answered by Head 2 · 0 1

wooo i just learned this last year in bio ... its sex cells

2006-10-24 00:25:25 · answer #8 · answered by Anonymous · 0 1

reproductive cells- sperm, ova, etc

2006-10-24 00:31:03 · answer #9 · answered by Earth Queen 4 · 0 1

Gametes - eggs or sperm

2006-10-24 00:20:06 · answer #10 · answered by FrescaBoy 2 · 0 1

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