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The zygote is the earliest developmental stage. In humans and most other anisogamous organisms, a zygote is formed when an egg cell and sperm cell come together to create a new unique organism. The formation of a totipotent zygote with the potential to produce a whole organism depends on epigenetic reprogramming.
The zygote contains the combined genetic material carried by both the male and female gametes which consists of the 23 chromosomes from the nucleus of the ovum and the 23 chromosomes from the nucleus of the sperm. The 46 chromosomes undergo changes prior to the mitotic division which leads to the formation of the embryo having two cells.
The main difference between the process of fusion of genetic materials in mammals versus sea urchins is that in sea urchins, the pronuclei go directly into forming a zygote nucleus. In mammalian egg cells, the chromatin from the pronuclei form chromosomes that merge onto the same mitotic spindle. The diploid nucleus in mammals is first seen at ...
The nucleus of the oocyte is called a pronucleus in this process, to distinguish it from the nuclei that are the result of fertilization. Drawing of an ovum. The sperm's tail and mitochondria degenerate with the formation of the male pronucleus. This is why all mitochondria in humans are of maternal origin.
Figure 1. depicts the process of nucellar embryony. A) begins with megaspore formation. B) shows the nucellus and forming of cells, nucellar embryonic initial cells, from the nucellus tissue. These initial cells form, divide, and expand. C) The nucellar embryos are developed. If and when a zygote is present, the nucellar embryos supersede the ...
The zygote, which will divide multiple times as it progresses throughout embryonic development, is one part of a seed. Other seed components include the endosperm , which is tissue rich in nutrients that will help support the growing plant embryo, and the seed coat, which is a protective outer covering.
Somatic cell nuclear transfer is a technique for cloning in which the nucleus of a somatic cell is transferred to the cytoplasm of an enucleated egg. After the somatic cell transfers, the cytoplasmic factors affect the nucleus to become a zygote.
Upon pollination, a pollen tube delivers sperm into the gametophyte and one sperm nucleus fuses with the egg nucleus. The resulting zygote develops into an embryo inside the ovule. The ovule, in turn, develops into a seed and in many cases, the plant ovary develops into a fruit to facilitate the dispersal of the seeds.