How does a cell select  genes which are retained in sexual reproduction?
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It is totally random, not decided in any way.\n\nWhen you toss a coin you 'reject' 50% of of the possible faces, since you can only select either heads or tails. How do you decide which faces to retain and which to reject? The answer of course is that you don't decide, it's pure random chance which one gets rejected and which gets kept. When chromosomes are assorted in meiosis it's pure random chance how they are distributed.\n\n_____________________\n>>>>>Not necessarily rejected. The cells split in two and >>>>>each one has 23 chromosomes. So the other cells are >>>>>used for the next time.\n\nNot in humans, no\n\nIn females the second cell is simply ejected as a polar body and dies. It is rejected in every sense of the word.\n\nAmongst males the second cell will go on to develop onto a spermatozoon simultaneously, nothing 'next time' about it. The odds of both cells being used to fertilise ova would be somewhat less than selecting the right grain of sand out of an entire beach. So for all practical purposes one of those cells will be rejected.
770439
Women are, men are not.\n\nIn men, the cells that go through meiosis eventually go through special phases to duplicate over and over and over and over and over.  4 gametes (sperm) are created each time for each male cell undergoing meiosis.\n\nFor gametes in women, the process of meiosis leaves one feasable gamete and 3 polar bodies that are discarded.  There cannot be 2 gametes because the cytoplasm must be given to the feasable gamete, along with all the other "good stuff", as the female gamete (egg) must be capable of starting life.\nWomen are born with about 10,000 cells that are capable of going through meiosis, and that is all there will ever be within a woman's body for their whole lifespan.\n\nIf the either sex was born with the gametes "ready to go" most of them would age and die before they were ever used- resulting in the end of the species, as, for humans, sexual reproduction is begun relatively "late" in life.  So, any "ready to go" cells would die before they were used, being useless to the continuation of the species.\n\nCells usually die every 4 months approximately.  Really really.  Except for nerve cells.  But if those die, they're gone.
952081
1. Usually all living cells of the same organism have the same exact DNA. But the cell type determines which genes are actually expressed.\n\n2. Eukaryote are more complex cells and have a longer time between transcription and a a functional protein. They use repression, signal cascades, phosphorylation, etc. A prokaryote has simpler regulation because transcription itself is usually the regulation.\n\n3. Vertebrates have 4 groups of hox genes, fruit flies only have one group. Look at the way the hox genes are expressed in development and what specifically they do (Sorry I can't give a more direct answer, I don't remember enough of my animal biology.)\n\n4. Polyploidy generally makes plants bigger, this makes their fruit bigger also. Another advantage is manipulation of fertilization. For example: seedless watermelon is produced by crossing a diploid with a tetraploid to get an infertile triploid. The embryos abort in the triploid and fail to form mature seeds.
678817
The basic mammalian body plan is female - and both genders go through similar early embryo development (including the development of nipples). Later in embryonic growth, genes on the X and Y chromosomes turn-on. These produce the various sex hormones that form the genitals and, in females, mammary glands.
318041
Meiosis is the process that transforms one diploid cell into four haploid cells in eukaryotes in order to redistribute the diploid's cell's genome.\n\nMeiosis forms the basis of sexual reproduction and can only occur in eukaryotes. In meiosis, the diploid cell's genome, which is composed of ordered structures of coiled DNA called chromosomes, is replicated once and separated twice, producing four haploid cells each containing half of the original cell's chromosomes. These resultant haploid cells will fertilize with other haploid cells of the opposite gender to form a diploid cell again. The cyclical process of separation by meiosis and genetic recombination through fertilization is called the life cycle. The result is that the offspring produced during germination after meiosis will have a slightly different blueprint which has instructions for the cells to work, contained in the DNA. This allows sexual reproduction to occur.\n\nMeiosis uses many biochemical processes that are similar to those used in mitosis in order to distribute chromosomes among the resulting cells; however the outcome is very different.
276439
Sexual reproduction speeds the evolutionary process in that it creates larger variance in genetic material between individuals.
2224
Gametogenesis is the process by which gametes (spermatocytes and ova) are produced in our body
17735
These two processes are mechanisms that increase genetic diversity in organisms that reproduce by sexual reproduction.
718212
dr d is correct.\n\nIt is transfer of genes within a generation, as compared to transfer from the parental generation to the offspring generation; that is vertical gene transfer between generations.\n\nIf genes are picked up from a cell in some way, and put into other cells (not involving cell division), then the genes have been transferred "horizontally".\n\nAn example is when a bacterium carrying a certain plasmid grows a "sex pilus", which then connects with the cell wall of a bacterium that does not carry that plasmid.  It will inject a copy of the plasmid, via the sex pilus, and the recipient has then become a carrier, too.  These plasmids often carry extra genes, as well as those coding for this ability.  These phenomena are sometimes considered to be similar to sex, but are really more like catching a virus!
1135410
DNA replication occurs when the cell needs to reproduce.  When the volume of the cell outgrows its surface area, a set of chemical signals are sent out notifying the DNA to begin replicating.  Asexual reproduction (fission) is the most common form of cell asexual reproduction.  Before sexual reproduction can occur you must first produce the gametes (sperm-eggs).  Here the DNA is replicated but then it is cut in half to produce the haploid gametes.  When the sperm and egg unite then the full complement of DNA returns.  This is not true in fission.
671131
Stored in the ovaries.
831327
Because egg and sperm cells have only one set of chromosomes instead of two.  Most cells have a pair of each type of chromosome, plus two chromosomes which determine the gender of the individual.  Mitosis, the normal process of cell reproduction, results in two cells which each have two sets of chromosomes.  Meiosis results in cells having only one set of chromosomes.\n\nThe reason egg and sperm cells have only one set of chromsomes is simple... after sex, an egg is fertilized by combining with a single sperm cell.  Once the egg and sperm (each having one set of chromosomes) have combined, the fertilized egg has two sets of chromosomes - everything it needs to grow and live.
576764
Asexual reproduction\n\n\nAsexual reproduction is the biological process by which an organism creates a genetically-similar or identical copy of itself without a contribution of genetic material from another individual. Bacteria divide asexually via binary fission; viruses take control of host cells to produce more viruses; Hydras (invertebrates of the order Hydroidea) and yeasts are able to reproduce by budding. These organisms do not have different sexes, and they are capable of "splitting" themselves into two or more individuals. Some 'asexual' species, like hydra and jellyfish, may also reproduce sexually. For instance, most plants are capable of vegetative reproduction—reproduction without seeds or spores—but can as well reproduce sexually. Likewise, bacteria may exchange genetic information by conjugation. Other ways of asexual reproduction include fragmentation and spore formation that involves only mitosis.\n\n\nSexual reproduction\n\nSexual reproduction is a biological process by which organisms create descendants that have a combination of genetic material contributed from two (usually) different members of the species. Each of two parent organisms contributes half of the offspring's genetic makeup by creating haploid gametes. Most organisms form two different types of gametes. In these anisogamous species, the two sexes are referred to as male (producing sperm or microspores) and female (producing ova or megaspores). In isogamous species the gametes are similar or identical in form, but may have separable properties and then may be given other different names. For example, in the green alga, Chlamydomonas reinhardtii, there are so-called "plus" and "minus" gametes. A few types of organisms, such as ciliates, have more than two kinds of gametes.\n\nHumans, most animals, and plants reproduce sexually. Sexually-reproducing organisms have two sets of genes for every trait (called alleles). Offspring inherit one allele for each trait from each parent, thereby ensuring that offspring have a combination of the parents' genes. Having two copies of every gene, only one of which is expressed, allows deleterious alleles to be masked, an advantage believed to have led to the evolutionary development of diploidy (Otto and Goldstein).
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D is the answer.  One cell differentiates and the other cell remains pleuripotent (has the ability to differentiate into many other types of cells).\nHere is why the other choices are incorrect.  Sometimes the other cell will die.  This happens in certain types of ground tissue, but only after the cell has differentiated into a specialized type of cell, which is why A is not the answer.  B is not the answer because gamete in plants is only formed by mitosis.  Only the gametophyte produces gametes and gametophytes are haploid so they only need to undergo mitosis to produce a gamete.  C is not the answer becuase the formation of a zygote requires the fusion of two cells, which does not happen under hte conditions of this question.
1093936
Mitosis is the reproduction of body cells.  Meiosis is the reproduction of gamet of sex cells and only have 23 chromosomes in them.
788311
A whole cell goes through it...including all of the chromosomes.\n\nA sex cell will duplicate its genome so that it has pairs of paired chromosomes...then it splits.  It then splits again so that there are 4 cells that are now haploid which means they only have 23 chromosomes instead of the diploid state of 46...well, for the human genome, anyway.  When two haploid cells(sperm and egg) come together they create a diploid zygote that develops into an embryo.
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In short Meiosis and Fertilisation.\n\nFertilisation brings each haploid gamete cell together, that is, a sperm and an egg. Each of these gametes carries a single copy of each chromosome. It is not until fertilisation that the chromosomes from each parent come together to form the diploid embryo.\n\nBut it's important to note that although we are walking around with 2 copies of our chromosomes, our gametes only have one. This is because the gametes are formed through the process of Meiosis, which halves our DNA. This allows the offspring to have a copy of each chromosome from each parent.