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The generic term polyploid is often used to describe cells with three or more sets of chromosomes. [ 4 ] [ 5 ] Virtually all sexually reproducing organisms are made up of somatic cells that are diploid or greater, but ploidy level may vary widely between different organisms, between different tissues within the same organism, and at different ...
The basic number of chromosomes in the somatic cells of an individual or a species is called the somatic number and is designated 2n. In the germ-line (the sex cells) the chromosome number is n (humans: n = 23). [4] [5] p28 Thus, in humans 2n = 46. So, in normal diploid organisms, autosomal chromosomes are present in two copies.
In biology, a biological life cycle (or just life cycle when the biological context is clear) is a series of stages of the life of an organism, that begins as a zygote, often in an egg, and concludes as an adult that reproduces, producing an offspring in the form of a new zygote which then itself goes through the same series of stages, the ...
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms.It is intended as introductory material for novices; for more specific and technical definitions from sub-disciplines and related fields, see Glossary of cell biology, Glossary of genetics, Glossary of evolutionary biology, Glossary of ecology ...
In the first stage of sexual reproduction, meiosis, the number of chromosomes is reduced from a diploid number (2n) to a haploid number (n). During fertilisation, haploid gametes come together to form a diploid zygote, and the original number of chromosomes is restored.
In diploid (2n) organisms, the genome is composed of one set of each homologous chromosome pair, as compared to tetraploid organisms which may have two sets of each homologous chromosome pair. The alleles on the homologous chromosomes may be different, resulting in different phenotypes of the same genes.
The equivalent terms haplodiplontic, diplobiontic and dibiontic are also in use, as is describing such an organism as having a diphasic ontogeny. [5] Life cycles of animals, in which there is only a diploid multicellular stage, are referred to as diplontic. Life cycles in which there is only a haploid multicellular stage are referred to as ...
They tend to be unstable and to lose further chromosomes during subsequent mitotic divisions, until the 2n+1 and 2n-1 nuclei progressively revert to n. Consistent with this, in E. nidulans (where normally, n=8) nuclei have been found with 17 (2n+1), 16 (2n), 15 (2n–1), 12, 11, 10, and 9 chromosomes.