Allele – Definition and Blood Type

Allele Definition Allele – any of the variations of a gene that may occupy the same position (locus) on a chromosome. The gene controlling a particular trait or function always occupies the same locus on the same chromosome. Genes occur as pairs, with one gene coming from each parent. The pairing determines how the gene’s traits are expressed in […]

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Replication Error

Replication Error Definition Replication Error – a mistake that occurs when dna sequences duplicate before cell division. Replication errors are accountable for chromosomal disorders such as autosomal trisomy, in which a gamete (also called a sex cell or germ cell) receives two copies of a chromosome instead of the normal single copy. Gametes, which are haploid cells, each carry one-half the complement of chromosomes […]

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Apoptosis – Definition and Cell Death

Definition of Apoptosis The natural mechanism through which a cell engages in actions that lead to its death, often called programmed cell death or cell suicide. Apoptosis appears linked to senescence, an inherent limitation on the number of times a cell can divide. Both apoptosis and senescence play significant roles in the aging process. Once the cell […]

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RNA – ribonucleic acid – Definition and Function

Ribonucleic Acid Definition RNA – the abbreviation for ribonucleic acid. RNA is a single-strand molecule consisting of ribose; a sugar; and nucleotides made up of the nitrogen bases adenine, uracil, guanine, and cytosine. RNA exists in a number of forms, all of which serve as biochemical messengers that carry the instructions of DNA to the ribosomes, […]

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Autosome – Definition

Autosome definition Autosome is a chromosome that appears as a pair in which both chromosomes are the same in either sex, also called a nonsex chromosome. In contrast, the sex chromosomes appear as a pair that is different in males and females. The human genome contains 22 autosomes and one pair of sex chromosomes for a total complement of 46 […]

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Senescence – Definition

Senescence Definition Senescence is the gradual and progressive slowing of cellular activity, including cell division, that occurs with aging. Cells lose the ability to divide over time, a phenomenon researchers call Hayflick’s limit. The limit relates to the number of times the cell divides. During cell division, fibers of dna called telomeres attach to the chromatids, facilitating their […]

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Cell Structure and Function

Cell Definition The cell is the basic structural and functional unit of all living organisms. About 100 trillion cells make up one of the most complex of such organisms, the human. Types of Cells in the Human Body There are three basic types of cells in the body: stem cells, germ cells, and somatic cells. […]

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Sex Chromosome – Definition

Sex Chromosome Definition The structure of genetic code that determines gender (male or female). The male sex chromosome has 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 […]

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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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