21.2 Heat resistance in rice. Rice is one of the most widely consumed grains world- study's wide. As increasing global temperatures hamper rice production, scientists are searching for varieties exhibiting some degree of heat resistance. The HT54 vari- of the indica rice, Oryza sativa, was found to tolerate several days of high ety temperatures up to 48 degrees Celsius (118 degrees Fahrenheit) during its growth. Researchers performed a genetic crossing experiment between the heat-resistant HT54 variety and a control variety, HT13, without heat resistance. All seedlings in the first generation survived a heat challenge of 48 degrees Celsius. In the sec- ond generation (F2), only 548 of the 744 plants survived the heat challenge. This would suggest that heat resistance is carried by a single gene with a dominant allele and a recessive allele. Are the findings consistent with a simple dominant- recessive Mendelian genetic model in which F2 is made up of 75% dominant-trait (heat resistance) and 25% recessive-trait rice plants? 4 la) Identify the variable and explain how you know that it is categorical. How many levels does this variable have? objective.