Nursing Preparation Study Guide

Nursing Preparation Study Guide

Law of Independent Assortment Mendel’s second law, the law of independent assortment, shows that the alleles of multiple genes will mix independently with one another. When two separate genotypes are tracked, the genes will produce 16 separate possible combinations spread out in a 9:3:3:1 ratio. This is also known as a dihybrid cross; when dealing with a single set of alleles, it is referred to as a monohybrid cross. We can demonstrate this by assuming that we have a male and a female each with heterozygous alleles making them blond and tall. We can represent this with the genotypes BbTt in each. We should also assume that a ‘bb’ genotype would give someone brown hair and ‘tt’ would make them short. Since the law of independent assortment purports that each allele will mix independently, we end up with four combinations of a genotype that each parent can pass on: BT, Bt, bT, and bt. These can then be mapped in a slightly larger Punnett square, which looks like this: BT Bt bT bt BT BBTT BBTt BbTT BbTt Bt BBTt BBtt BbTt Bbtt bT BbTT BbTt bbTT bbTt bt BbTt Bbtt bbTt bbtt This is the distribution of the tall, blond couple’s possible children. Nine would also be tall and blond, three would be short and blond, three would be tall and brunette, and one would be short and brunette. This follows the 9:3:3:1 ratio set out by Mendel. 9.2.4 Atomic Structure Atoms Atoms are some of the basic building blocks of matter. Each atom is an element, an identifiable substance that cannot be further broken down into other identifiable substances. There are just over 100 such elements, and each of them can combine with themselves andwith other elements to create all the various molecules that exist in the universe. The poison gas chlorine and the explosive metal sodium, for instance, can combine at the atomic level to form sodium chloride, also known as salt. For thousands of years, atoms were thought to be the smallest thing possible. The word “atom” comes from an ancient Greek word meaning “unbreakable”. However, experiments performed in the mid- to late-19 th century began to show the presence of small particles, known as electrons, in electric current. By the early 20 th century, the electron was known to be a part of the atom that orbited a yet undefined atomic core. A few years later, in 1919, the proton was discovered and found to exist in the nuclei of all atoms.

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