Mendelian Inheritance Patterns

Mendelian Inheritance Patterns

Scientists use a grid-like tool (Punnett Square) to make predictions about various genetic problems. The Punnett Square shows only the probability (the chance of something occurring) of what might occur and not the actual results. For example, if one wants to flip a coin 100 times, since there are 2 sides to the coin, they can expect 50 heads and 50 tails. However, if you actually flip the coin 100 times, you may actually get 60 heads and 40 tails. Punnett Squares only show the chances of what might occur each time the event is undertaken. They do not show the actual outcome. Recall that Mendel formulated the First Law of Inheritance which states that: Each organism contains two alleles for each trait (gene), and the alleles segregate (separate) during formation of gametes. Each gamete (egg or sperm) contains only one allele for each gene. Upon fertilization, the resulting offspring will have two alleles for each trait – one from each parent. Using a Punnett square, we can predict the possible genotypes and phenotypes of resulting offspring, when crossing two parents whose genotypes are known.