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The list of organisms by chromosome count describes ploidy or numbers of chromosomes in the cells of various plants, animals, protists, and other living organisms.This number, along with the visual appearance of the chromosome, is known as the karyotype, [1] [2] [3] and can be found by looking at the chromosomes through a microscope.
The result is a genetic condition in which a person has 47 chromosomes instead of the usual 46. During egg or sperm development the 21st chromosome does not separate during either the egg or sperm development. The result is a cell that has 24 chromosomes. This extra chromosome may cause problems with the manner in which the body and brain ...
During the primary oocyte stage of oogenesis, the nucleus is called a germinal vesicle. [2] The only normal human type of secondary oocyte has the 23rd (sex) chromosome as 23,X (female-determining), whereas sperm can have 23,X (female-determining) or 23,Y (male-determining).
The 23 rd chromosome base pair contains what are known as our sex chromosomes. For most females, this pair contains two X chromosomes, while for most males, it contains one X chromosome and one Y ...
In humans, each cell nucleus contains 23 pairs of chromosomes, a total of 46 chromosomes. The first 22 pairs are called autosomes. Autosomes are homologous chromosomes i.e. chromosomes which contain the same genes (regions of DNA) in the same order along their chromosomal arms. The 23rd pair of chromosomes are called allosomes.
Most mammalian females have two copies of the X chromosome, while males have only one X and one smaller Y chromosome; some mammals, such as the platypus, have different combinations. [ 28 ] [ 29 ] One of the female's X chromosomes is randomly inactivated in each cell of placental mammals while the paternally derived X is inactivated in marsupials.
All animals have a set of DNA coding for genes present on chromosomes. In humans, most mammals, and some other species, two of the chromosomes, called the X chromosome and Y chromosome, code for sex. In these species, one or more genes are present on their Y chromosome that determine maleness.
The XX/XY sex-determination system is the most familiar, as it is found in humans. The XX/XY system is found in most other mammals, as well as some insects. In this system, females have two of the same kind of sex chromosome (XX), while males have two distinct sex chromosomes (XY).