2n 14 how many gametes

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Body Systems. Medical Exams. Medical Subspecialties. Medical Terminology. Misc Healthcare Topics. Nursing Subspecialties. Other Healthcare Fields. Home Economics. Interior Design. The microspores develop into binucleate pollen grains, each containing a tube nucleus and a generative nucleus. When the pollen grain lands on a receptive stigma it grows into an elongate pollen tube containing a tube nucleus and a generative nucleus, the latter of which divides into two sperm nuclei.

A binucleate angiosperm pollen grain containing a generative nucleus and a tube nucleus. After the pollen grain germinates into a pollen tube, the generative nucleus divides into two sperm nuclei.

Because the generative nucleus and sperm nuclei contain cytoplasmic sheaths, they are often referred to as cells in some textbooks. The tube nucleus controls the growth of the pollen tube as grows down the style and into the ovary of a flower. Eventually it penetrates the micropyle of an ovule and releases its two sperm into the 8-nucleate embryo sac.

During double fertilization, one sperm fuses with the egg nucleus to form a zygote. The other sperm fuses with the two polar nuclei inside the endosperm mother cell to form the endosperm. In corn, this process must occur for each grain that forms. Even more astonishing is the growth of separate pollen tubes down each strand of silk styles. A diploid megaspore mother cell inside each ovule also undergoes meiosis megasporogenesis and forms four haploid megaspores, three of which abort leaving one functional megaspore.

The functional megaspore inside each ovule undergoes nuclear division into a 7-celled, 8-nucleate embryo sac. At one end of the embryo sac are three antipodal cells. At the opposite end is an egg cell flanked by two synergid cells. A large binucleate cell in the center containing two polar nuclei is called the endosperm mother cell. During pollination, pollen grains land on the stigma where they form pollen tubes that penetrate the style and eventually the ovary of the flower.

A separate sperm-bearing pollen tube must reach each ovule in order to fertilize the egg cell inside the embryo sac.

During double fertilization two sperm are introduced into the embryo sac from the long pollen tube. One sperm nucleus fuses with the egg nucleus inside the egg cell to form a diploid 2n zygote which develops into the embryo of the seed.

The other sperm nucleus fuses with the two polar nuclei inside the endosperm mother cell to form the tripolid 3n endosperm of the seed. Microscopic view of the embryo sac megagametophyte of a lily Lilium.

Three haploid antipodal cells 1 occur at the upper end of the emryo sac. A large endosperm mother cell containing two haploid polar nuclei 2 occupies the central portion of the embryo sac. At the lower end nearest the micropyle and funiculus are two haploid synergid cells 3 and one haploid egg.

The embryo sac contains a total of seven cells and eight nuclei. The sporophyte generation includes the stems, leaves, roots, flowers, fruits and seeds. After fertilization, the ovule enlarges and develops into a mature seed containing a diploid zygote and triploid endosperm. The seed coat is chromosomally identical to the female parent ovary tissue because it was derived from two outer layers of the ovule called the integument the integument of gymnosperm ovules consists of a single layer.

On a mature seed the opening or pore in the seed coat is where the pollen tube once entered a gap in the integument layers called the micropyle.

As the ovules develop into seeds, the outer ovary encasing the ovules enlarges and ripens into a fruit. Fruits that develop without double fertilization and without seeds are termed parthenocarpic. Examples of parthenocarpic fruits are navel oranges, bananas, seedless watermelons, and certain varieties of figs. Not all seedless fruits are parthenocarpic. In Thompson seedless grapes, fertilization does occur, but the ovules fail to develop within the fruit. Parthenocarpy can be induced artificially by the application of dilute growth hormone sprays such as auxins to the flowers, as in seedless tomatoes.

Seedless watermelons come from triploid sterile plants; however, to set fruit they must be pollinated by a fertile diploid plant. Some embryos of seeds can develop apomictically without fertilization.

A number of angiosperm families contain apomictic species, including figs, blackberries, hawthorns and dandelions. The embryo may develop from a diploid nutritive cell nucellus tissue surrounding the embryo sac or from the fusion of hapolid cells within the embryo sac. In general there are two main types of apomixis: [1] Parthenogenesis agamogenesis : A haploid or diploid egg within the embryo sac or diploid cell from 2 fused haploid cells of embryo sac develops into an embryo.

If this involves cells of the nucellus or inner integument layer it is called a nucellar embryo. Nucellar embryos are chromosomally identical to the sporophyte parent. They are essentially clones of the female parent. In varieties of the edible fig Ficus carica , apomictic seeds allow propagation of choice edible fig cultivars female trees without the transmission of viruses through cuttings. Apomixis also enables a pioneer seedling to colonize and become naturalized in a new habitat by reseeding itself without cross pollination.

Since the seed coat originates from the outer wall of the ovule called the integument , which was part of the original maternal seed parent, it is chromosomally identical with the original diploid seed parent. The mature pollen grain contains a tube nucleus and generative nucleus, the latter of which divides into two sperm nuclei within the pollen tube.

All of these pollen nuclei are chromosomally identical with each other and with the sperm nuclei. The following diagram summarizes double fertilization in this question: [Botany students: Remember that in your question the diploid pollen parent is aabbccdd and the sperm would be abcd; the diploid seed parent is AABBCCDD and the egg would be ABCD.

The following remarkable Wayne's Word image shows a minute diploid coconut embryo embedded in the triploid, meaty endosperm within the seed of a coconut palm. Close-up view through the inside of a coconut seed showing a small, cylindrical embryo A embedded in the fleshy meat or endosperm B. The base of the embryo pointing into the coconut swells into an absorbing organ cotyledon that fills the entire cavity of the seed as it digests the endosperm.

The wall of the endocarp C is a hard, woody layer that makes up the inner part of the fruit wall. The thick, fibrous husk mesocarp that surrounds the endocarp has been removed.

Sprouting fruit of a coconut Cocos nucifera. The hard inner layer endocarp contains the actual seed composed of a minute embryo and food storage tissue endosperm.

The base of the embryo cotyledon swells into an absorbing organ that fills the entire cavity of the seed as it digests the endosperm.

The endocarp has three germination pores, one functional pore and two plugged pores. Type A spermatogonia divide by mitosis to form either more type A spermatogonia to maintain the supply or type B spermatogonia. Under the influence of estrogen released during the first half of the menstrual cycle , three changes take place in the uterine tubes to facilitate its capture of the egg:. The uterine tubes move closer to the ovaries physical approximation. The fimbriae on the ends of the tubes beat more rapidly increased fluid current.

The number of ciliated cells in the epithelium of the fimbriae increase increase in ciliation. Sperm are deposited in the upper vagina and must overcome several obstacles to reach an egg in the ampulla of one of the uterine tubes.

The egg itself is viable for only about 24 hours. Table 1 - Obstacles to Sperm Transport. The alkaline seminal fluid temporarily neutralizes the normal acidity pH 4. The composition of cervical mucus changes during menstrual cycle. Sperm can most easily penetrate the thinner E-mucus that predominates during the last few days before ovulation, as opposed to the thicker G-mucus.

Two modes of transport:. Slow — the rest of the sperm swim their way up the last part of the cervical tube, are stored in cervical crypts folds of the cervix , and are slowly released into the uterus over days.

Table 2 - Karyotypes of Germ Cells and Gametes. Primordial germ cell. Primary oocyte. Secondary oocyte. Mature oocyte. Type A spermatogonium. Type B spermatogonium.