Interpreting Data from Tables Practice Test

PASSAGE VI

BIOLOGY / GENETICS: Research Summary

Introduction

Restriction enzymes are proteins that cut DNA molecules at specific, predictable sequences of base pairs (bp). Gel electrophoresis is a technique used to separate these resulting DNA fragments by size. When an electrical current is applied to the gel, the negatively charged DNA fragments migrate toward the positive electrode. Smaller DNA fragments move through the gel much faster and travel further than larger fragments.

A researcher isolated a circular bacterial plasmid (a ring of DNA) consisting of exactly 5,000 bp. To map the plasmid, the researcher treated identical samples of the plasmid with different restriction enzymes—Enzyme 1 (E1), Enzyme 2 (E2), and Enzyme 3 (E3)—both individually and in combinations.

After allowing the enzymes to cut the DNA, the researcher ran the samples on an electrophoresis gel. A dye was added to make the DNA bands visible. The size of the fragments in each band was recorded in Table 1.

PASSAGE VI

Fruit Fly Genetics

Introduction

In the fruit fly Drosophila melanogaster, eye color is a sex-linked trait determined by a gene on the X chromosome. The allele for the wild-type red eye color ($$X^R$$) is dominant, while the allele for the mutant white eye color ($$X^r$$) is recessive.

Females (XX): Inherit one X chromosome from each parent. A female will have white eyes only if she is homozygous recessive ($$X^r X^r$$).

Males (XY): Inherit an X chromosome from the mother and a Y chromosome from the father. Because the Y chromosome does not carry the eye color gene, a male expresses whichever allele is present on his single X chromosome ($$X^R Y = Red; X^r Y = White$$).

Students conducted two studies to observe these inheritance patterns.

Study 1

The students crossed a homozygous red-eyed female ($$X^R X^R$$) with a white-eyed male ($$X^r Y$$). To predict the genotypes of the offspring, they constructed a Punnett square (Figure 1).

They then collected 100 offspring (the F1 generation) and recorded the results in Table 1.

Study 2

The students performed the reciprocal cross. They crossed a white-eyed female ($$X^r X^r$$) with a red-eyed male ($$X^R Y$$). A second Punnett square was constructed to predict the outcome (Figure 2).

They collected 100 offspring and recorded the results in Table 2.