Science practice 48

The most common type of red-green color perception defect is caused by a mutation on the X chromosome. X-linked red color blindness is a recessive trait. The eggs of the mother will contain either a normal X chromosome (X^R) or an X chromosome with the mutation (X^r) causing red-green color blindness. The sperm of the father will contain the normal X chromosome, the X chromosome with the mutation, or the Y chromosome. Females heterozygous (one normal gene, one mutated gene) for this trait have normal vision. The color perception defect manifests itself in females only when it is inherited from both parents. By contrast, males inherit their sole X chromosome from their mothers, and become red-green color blind when this one X chromosome has the color perception defect.

Genotype refers to the combination of alleles that an individual has for a gene. Table 1 lists the possible genotypes for red-green color perception and their corresponding effects on vision.

Table 1

Students interviewed members of the Allen family to investigate the inheritance of red-green color blindness.

Figure 1 displays the family tree of the Allen family.

Figure 1

Study 1

Students interviewed Barbara and John and learned that Barbara is red-green color blind, while John is not. Based on this information, the students deduced that their four children have the following genotypes:

Figure 2

Study 2

Students assumed that Liz would have children with a man who has normal vision, and using a Pundit square calculated all of the possible genotypes for their children:

Figure 3

Study 3

Students assumed that David would have children with a woman who has red-green color blindness, and using a Pundit square calculated all of the possible genotypes for their children:

Figure 4

Crude oil contains many different types of carbons. Different carbon chain lengths have different boiling points, so they can be separated using distillation—the process of boiling and then condensing a liquid in order to separate and purify its components (see Figure 1).

Figure 1

Crude oil is put into a boiler. The boiler is connected to a distillation column filled with collection trays. As the heated oil boils, the vapors released enter the distillation column and rise to the top. When a substance in the vapor reaches a height where the temperature of the column is equal to that substance’s boiling point, it will condense to form a liquid. The liquid is gathered on the collection trays.

Experiment 1

Students determined the boiling points of various components of crude oil by recording the temperature of the vapor at various heights in the distillation column, then determining which component was collected in each of the eight collection trays. See Table 1 and Table 2.

Table 1

Table 2

The students distilled one barrel of crude oil. Figure 2 shows the breakdown of that barrel, in terms of which components were collected.

Figure 2

Experiment 2

Students determined the number of carbons in each component of crude oil and recorded the data in Table 3.

Table 3