Wendy Wilson Spooner ~ Genetic Genealogist, Lic. G., LCoT
Genes are composed of segments of DNA, and in ordinary cell-nuclei the DNA is dispersed within 46 chromosomes (one set of 23 from the father, and one set of 23 from the mother). Every chromosome carries thousands of genes (Genes and DNA, 2014) and each time a cell divides, the cell copies the 46 chromosomes and distributes one reproduction of each to the two new cells (Hart, 2002).
Genes can be manifest as either recessive or dominant. Only when the dominant trait is absent, can the recessive gene appear. These facts imply the presence of two versions of each characteristic; one inherited from the father, and one from the mother. These alternate versions are called alleles. Even though dominant traits disguise the presence of recessive traits, the dominant trait is not necessarily superior to the recessive, nor is it more likely to be passed on to the next generation (Smolenyak and Turner, 2004).
From the parents, children have a 50 percent chance of inheriting one allele or the other, which is the main reason siblings can be so different. Current research shows that some characteristics are associated by lying closely together on the same chromosome, and are therefore inherited as a package. As well, other gene attributes show that some characteristics have more than two alleles; some characteristics are co-dominant, and sometimes the sex of the parent influences weather or not certain traits are expressed (Smolenyak and Turner, 2004, p. 21). Also, during meiosis of one paternal and one maternal chromosome, a cross may transpire in an exchange of parallel sections of DNA and the rejoining of the chromosomes, which can result in the exchange of alleles (Hart, 180).
In conclusion, the set of genes that an organism carries is called a genotype, and all of an organism's observable characteristics are called a phenotype (Inheritance of Traits by Offspring Follows Predictable Rules, 2014). The manner in which a genotype translates to a phenotype is through “transcription to RNA via translation to protein; proteins can act to alter the patterns and timing of gene expression which can lead to cytodifferentiation where cells take on different states; cell communication can lead to pattern formation and morphogenesis and eventually an adult organism” (Phenotype and Genotype, 2014). Since an organism’s genotype normally impacts its phenotype, the phenotypes that make up a population will probably change. An example of a geneotype producing a different phoenotype can be seen in a cat with curled ears, versus a cat with straight ears (Genotype Versus Phenotype, 2014).
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Hart, Anne. How to Interpret Your DNA Test Results for Family History. New York Lincoln Shanghai: Writers Club Press, 2002.
“Inheritance of Traits by Offspring Follows Predictable Rules.” Scitable: By NatureEducation. April 3, 2014. Accessed April 3, 2014. http://www.nature.com/scitable/topicpage/inheritance-of-traits-by-offspring-follows-predictable-6524925.
“Phenotype and Genotype.” Brown University: Division of Biology and Medicine. March 31, 2014. Accessed March 31, 2014. http://biomed.brown.edu/Courses/BIO48/5.Geno.Pheno.HTML.
Smolenyak, Megan S, and Ann Turner. Trace Your Roots with DNA: Using Genetic Tests to Explore Your Family Tree. Rodale Books, 2004.