InheritancePatterns211

InheritancePatterns211 - Inheritance Patterns - 1 All of us...

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Inheritance Patterns - 1 All of us are familiar with inheritance – the characteristics of organisms that are passed from generation to generation. We readily compare facial features of children to their parents remarking at similarities (or differences) and often select our pets based on pedigree (their genetic heritage). We know that our genetic information is stored in DNA that is passed from cell to cell and from generation to generation as inheritable characteristics. We know, too, that for most inheritable characteristics there are at least two different variants, or traits, possible – that's why we have differences in inheritance. The region of a DNA molecule that stores a specific genetic instruction is called a gene. The precise location where a gene is found on a chromosome is known as the locus for the gene. Since chromosomes of diploid organisms come in homologous pairs, each cell of a diploid organism typically has two "genes" or a "gene pair" for each inheritable trait, one on each of the homologues. The alternative forms (variants) of genes are located on the homologous chromosomes and are called alleles. Alleles are the specific traits for the gene. For example, we may grow a plant in our garden for a particular flower color, for which there are two variants (or alternative forms) – white or purple. The gene is a description of the flower color. The alleles for that gene are white or purple. To be precise, we inherit alleles of the homologous chromosomes or "gene pair". A haploid gamete has one allele of each "gene pair" (or one of each homologous chromosome) but not both. The diploid number of chromosomes is restored at fertilization along with the homologous chromosomes and gene pairs when two gametes fuse. In this section of biology we will look at how genes (alleles) are expressed in individuals, and how genes (alleles) are transmitted from generation to generation within species.
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Inheritance Patterns - 2 We did not always know that genes were located on chromosomes. We did not even know that inheritable traits, or genes, came in pairs. Gregor Mendel, in the mid- 1800s, was the first to publish that inheritable traits (genes) were discrete units that came in pairs with scientific evidence to validate his conclusions. His work went unappreciated for several decades because no one seemed to understand what it meant. In the early 1900's, three plant geneticists, Hugo DeVries, Carl Correns and Erich von Tschermark, independently made the same conclusions about inheritance, and Mendel's papers were "rediscovered". Soon after, Walter Sutton showed that Mendel's principles of inheritance applied to chromosomes and that chromosomes are the units of heredity, which resulted in the chromosome theory of inheritance. Prior to Mendel, the subject of inheritance was mostly guesswork even though the
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InheritancePatterns211 - Inheritance Patterns - 1 All of us...

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