Sex Chromosome – definition

Sex Chromosome Definition The structure of GENETIC CODE that determines gender (male or female). The male sex CHROMOSOMEhas the appearance of the letter Y and the female sex chromosome has the appearance of the letter X. A combination of XY results in male and a combination of XX results in female. The Y chromosome contains fewer than 100 genes, […]

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Centromere – function and definition

Centromere Definition The position on a CHROMOSOME where the chromosome separates during cell division. The centromere is a structure of noncoding DNA (DNA that does not convey genetic information). When the cell divides the strands of the chromatids migrate in opposite directions (pull apart) at the centromere. In a photomicrograph, the centromere appears as an indented, waistlike area on the […]

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Somatic Cell – definition

Somatic Cell Definition Somatic Cell – a cell that is not a GAMETE (sex cell). More than 99 percent of the body’s trillions of cells are somatic cells. Somatic cells are diploid; their nuclei contain the full complement of paired chromosomes and genetic material necessary to encode an organism. When somatic cells divide, their chromosomes replicate so the […]

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Chromatid – definition

Chromatid Definition Chromatid is a replica of a CHROMOSOME that develops in preparation for cell division. Chromatids are “sister” pairs of each chromosome that contain identical genetic material. They remain attached to each other at the CENTROMERE until cell division. When the mother cell divides, the sister chromatids separate at the centromere and migrate into the new daughter cells, forming […]

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Stem Cell – what is, function and information

Stem Cell Definition Stem Cell – an undifferentiated, primal cell that has the capability to endlessly divide and develop into numerous types of cells.Totipotent stem cells exist primarily in the early EMBRYO (blastocyst) and can differentiate into (become) virtually any type of cell in the body. As the body becomes more complex and develops beyond […]

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Chromosome – what is, definition and function

Chromosome Definition A coiled DNA molecule within the cell’s nucleus that carries an individual’s GENETIC CODE. Most of the time the chromosome’s structure is loose and indistinguishable. Only in the stage of cell division immediately before the cell divides (the metaphase) does the chromosome draw itself into a compact, rodlike structure the geneticist can see under a microscope after […]

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Telomere – definition

Telomere Definition A structure of noncoding DNA (DNA that does not convey genetic instruction) at each end of a CHROMOSOME. Telomeres are essential for chromosome duplication during cell division. They function as handles to pull the chromatids (dividing chromosomes) apart as the mother cell divides into the two new daughter cells. The process of cell division permanently destroys a […]

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DNA – deoxyribonucleic acid – definition and function

Deoxyribonucleic Acid Definition DNA – the abbreviation for deoxyribonucleic acid. DNA is the molecule of heredity; its sequences form the body’s GENETIC CODE. Each cell in the body contains DNA within the chromosomes in its nucleus (except erythrocytes, which do not have nuclei). DNA has a characteristic double-helix structure that resembles a gently twisting ladder. The supporting […]

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Variation (genetic) – definition

Variation Definition The genetic differences among individuals. There are trillions of possible GENE combinations within the human GENOME. Except for identical twins, no two people share exactly the same GENOTYPE (genetic constitution). Though any two individuals may have 99.9 percent of the same DNA sequences and gene pairings, the 0.1 percent of pairings that differ accounts for the endless details that make each […]

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Gamete – definition

Gamete Definition Gamete is a spermatozoon (SPERM cell) or an ovum (egg cell). A gamete, also called a germ cell or sex cell, is a haploid cell; it contains half the complement of chromosomes and genetic material necessary to encode (result in creating) an individual. When two gametes merge they produce a single diploid cell, the ZYGOTE, […]

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