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The study of genetics presents a fine opportunity to address some of these misconceptions.  One basic misunderstanding students have stems from their lack of knowledge of independent and dependent events.  "If you and your husband (wife) are considering having a third child and you already have had two happy and healthy sons, are you more or less likely to have a daughter the next time?"  This question addresses the influence that recent events have on the outcome of future events.   Students are often misguided to believe that recent events will have an influence on the outcome of future events.  Fischbein and Schnarch referred to this as the Negative and Positive Recency Effects (p.98) or the "We are due" affect.  "We have had three boys, so we are due to have a girl." Or,  "I have gotten B's on the last three genetics tests, so I am due for an A!" 

The concept that the students must understand in order to correct this fallacy  is that some events, such as the gender of a baby, are independent events.  The outcome of one event does not affect the outcome of the next. In other words, the birth of a girl does not increase the odds of a birth of a boy the next time. As the students will learn in the Genetics Lesson, the odds of having a child with the genotype XY are 50/50, which implies the same for having the genotype of XX.  

*Link to the True or False? Lesson Plan that addresses this misconception.