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Speciation via polyploidy: A diploid cell undergoes failed meiosis, producing diploid gametes, which self-fertilize to produce a tetraploid zygote. Polyploidy is frequent in plants, some estimates suggesting that 30–80% of living plant species are polyploid, and many lineages show evidence of ancient polyploidy (paleopolyploidy) in their genomes.
Even in diploid organisms, many somatic cells are polyploid due to a process called endoreduplication, where duplication of the genome occurs without mitosis (cell division). The extreme in polyploidy occurs in the fern genus Ophioglossum , the adder's-tongues, in which polyploidy results in chromosome counts in the hundreds, or, in at least ...
Animals have life cycles with a single diploid multicellular phase that produces haploid gametes directly by meiosis. Male gametes are called sperm, and female gametes are called eggs or ova. In animals, fertilization of the ovum by a sperm results in the formation of a diploid zygote that develops by repeated mitotic divisions into a diploid ...
This process is called zona hatching and it takes place on the sixth day of embryo development, immediately before the implantation process. The hatching of the human embryo is supported by proteases secreted by the cells of the blastocyst, which digest proteins of the zona pellucida, giving rise to a hole.
In biological terms, human development entails growth from a one-celled zygote to an adult human being. Fertilization occurs when the sperm cell successfully enters and fuses with an egg cell . [2] The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of prenatal development commences.
Polyploidy, or whole genome duplication is a product of nondisjunction during meiosis which results in additional copies of the entire genome. Polyploidy is common in plants, but it has also occurred in animals, with two rounds of whole genome duplication in the vertebrate lineage leading to humans. [4]
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.
This is an accepted version of this page This is the latest accepted revision, reviewed on 22 January 2025. Union of gametes of opposite sexes during the process of sexual reproduction to form a zygote This article is about fertilisation in animals and plants. For fertilisation in humans specifically, see Human fertilization. For soil improvement, see Fertilizer. "Conceive" redirects here. For ...