Haploid cell

Ponzetto, C., Wadewitz, A. G., Pendergast, A. M., Witte, O. N., and Wolgemuth, D. J. (1989). P I50c ai,/is detected in the mouse male germ line by an in vitro kinase assay and is associated in haploid cells with a stage-specific phosphoprotein. Oncogene 4 685-690. 

Haploid cells have only a single copy of each chromosome. This occurs normally in the mature germ cell. Diploid cells, in contrast have two copies of each chromosome most normal somatic cells are diploid. The fact that yeast cells are haploid renders genetic analysis much easier because one has taken sex out of the equation - the question remains whether it is as much fun ... 

Meiosis is cell division that produces two daughter cells with only half the number of chromosomes of the parent cell these are haploid cells. It occurs during the formation of spermatozoa and ova. The normal number of chromosomes is then achieved at fertilisation of an ovum by a spermatozoon. Meiosis also results in crossing over , which is the physical reciprocal exchange of parts... 

Musc/skel = musculoskeletal N = haploid cells 4N = polyploid cells NOAEL = no-observed-adverse-effect level NS = not specified Resp = respiratory (W) = water wk = week(s)... 

Yeast cells can exist as haploids of opposite mating types (either a or a). When an a and an a cell are allowed to mate, they form a diploid cell (a/a). To study interactions between two proteins, cDNA sequences of a protein of interest (PT1) are expressed as a fusion protein, linked to a DNA-binding domain (DBD) of a yeast gene-transcript activator in a haploid cell (e.g., a). cDNA sequences corresponding to another test protein (PT2) are linked to the Continued on next page)... 

Some other transposons. Transposons have a variety of biological functions. For example, haploid cells of the yeast S. cerevisiae exist as one of two mating types a or a. The mating type is established by transposition of one of two "cassettes" of genes from two different "silent" locations to a location from which they can be expressed.623 624 See Chapter 28. 

Cells that carry a single copy of each gene are referred to as haploids. Cells that carry two copies of each gene are referred to as diploids. Bacteria are haploid cells because they carry a single chromosome with a unique representation for each gene. Bacterial cells that are partial diploids (merodiploids) may occur naturally, or they may be selected for by genetic techniques. 

Yeast has two haploid cell mating types MATa (or simply a) and MATa (or a) on contact, haploid cells of opposite mating types fuse to form a single diploid ala) cell. Diploid cells can grow and divide indefinitely as diploid cells, or they can sporulate, a process in which they undergo mei-osis and give rise to two a and two a cells for each diploid cell. The haploid mating type is determined by specific sequences at the MAT locus (fig. 31.5). These sequences are found at the HMLa or HMRa loci, where they are usually not expressed. When the sequences stored at the HMLa locus are transposed to MAT, they express similarly when sequences are transposed from HMRa to MAT, they express. 

An important question remaining is how does a single genetic locus determine the haploid yeast cell mating type Haploid cells that carry MATa behave as a cells similarly... 

Regulation of a-specific genes (asg) and a-specific genes (asg) in a and a haploid cells. In an a cell, a2 inhibits asg and a 1 activates asg. In an a haploid cell, the al transcript made at MATa does not appear to exert any regulatory function. ( = positively regulated ... 

Regulation of meiosis in yeast. Haploid cells are not able to initiate meiosis because they express RME1, which is a negative regulator of meiosis. Diploid cells are able to initiate meiosis because they make a complex of al and a 1 that inhibits the synthesis of the RME 1 product. 

Gametes. The ova and the sperm, haploid cells that unite during fertilization to generate a diploid zygote. 

Haploid cell. A cell containing only one chromosome of each type. 

DISOMIC Having two of a given chromosome in an otherwise haploid cell or organism. 

Because meiosis is a property of diploid rather than haploid cells,... 

The observation of only one morphotype in P. scrobiculata and P. cordata suggests either that the whole cycle has not been yet observed, or these species lose the ability to form colonies. The assumption of Vaulot et al. (1994) that filaments forming five- or nine-rayed stars are associated with haploid cells suggests that Phaeocystis would occur as haploid flagellates in oceanic and oligo-trophic environments. 

Nonsense mutations and Tn5 insertions in secB are tolerated in haploid cells, indicating that secB is not an essential gene. However, secB null strains are sensitive to rich media and do not form isolated colonies on LB agar plates (Kumamoto and Beckwith, 1985). Induction of the heat-... 

Fig. 2.1. Mating between haploid MATa and MATa cells in S. cerevisiae. Each haploid cell secretes a unique pheromone that binds to a G-protein-conpled receptor on the opposite mating type, initiating a signaling cascade that promotes cell and nnclear fnsion to form the diploid MATa/a cell.

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