Haploid number

All nucleated cells except eggs and sperm (gametes) carry two sets of genetic material in their nuclei, one from the individual s mother and one from the father, hi human cells there are 22 pairs of homologous chromosomes plus an X chromosome and a Y chromosome. In the formation of gametes, this must be reduced to a single set, that is, the diploid number of chromosomes (46) must be reduced to the haploid number (23). 

ANEUPLOID An organism or cell whose somatic nuclei do not contain an exact multiple of the haploid number of chromosomes, one or more chromosomes being represented more (or fewer) times than the rest. (See also MONO-SOMIC and TRISOMIC)... 

Euploid The situation that exists when the nucleus of a cell contains exact multiples of the haploid number of chromosomes. 

In vertebrates and diploid yeasts, cells in Gi have a diploid number of chromosomes (2/i), one inherited from each parent. In haploid yeasts, cells In Gi have one of each chromosome (l/i), the haploid number. Rapidly replicating human cells progress through the full cell cycle In about 24 hours mitosis takes —30 minutes Gi, 9 hours the S phase, lO hours and G2, 4.5 hours. In contrast, the full cycle takes only —90 minutes In rapidly growing yeast cells. 

Meiosis is similar to mitosis, but there are two consecutive cell divisions, meiosis I and meiosis II in order to reduce the chromosome number by one half. This way, when the sperm and egg join during fertilization, the haploid number is reached. 

If haploid cells fuse, nuclear fusion follows and a diploid nucleus (one containing two sets, twice the haploid number, of chromosomes) is formed. The immediate product of such a fusion process is termed a zygote. From the zygote develop diploid cells which reproduce vegetatively by budding the nucleus divides mitotically and the cells are said to be in the diplophase. 

The number of unique chromosomes is called the haploid number (N), but there are two copies of each, and 2N is called the diploid number. 

The main difference between the second meiotic division and the classical mitosis resides in the fact that the second meiotic division involves a haploid number of chromosomes. 

Aneuploidy is a deviation from an exact multiple of the haploid number of chromosomes. For example, if the normal diploid chromosome number is 46 (haploid = 23), then 47 chromosomes would be an aneuploid condition. 

The Fj progeny were normally viable and fertile. From these data it can be determined that the presence of a haploid number of chromosomes from the same species as the cytoplasm determines normal embryonic development. 

Like other members of the genus Pinus, the haploid number of chromosomes is 12 in western white pine (Saylor and Smith, 1966). Chloroplasts are inherited predominantly paternally, while mitochondria are primarily inherited maternally, although some biparental inheritance of organelles can occur (White, 1990 Owens and Bruns, 2000). At the time of fertilisation, maternal plastids are excluded from the neocytoplasm but maternal mitochondria remain. Paternal chloroplasts and a small number of paternal mitochondria are released into the egg from the pollen tube with cytoplasm from the tube cell and generative cell. Maternal mitochondria migrate to and aggregate in the perinuclear zone at the time of fertilisation (Bmns and Owens, 2000). 

All species of Larix, like most other genera in the Pinaceae, have a haploid number of 12 chromosomes (Wright, 1962). Polyploidy and aneuploidy are rare in conifers. A cross between L. occidentalis and L. decidua (European larch) produced a single triploid hybrid (Larsen and... 

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