BIOL-101 Lesson 17: Molecular Basis of Inheritance

Q: What organism did T. H. Morgan use to show that genes are located on chromosomes?

A: Drosophila melanogaster (fruit flies).

Q: Why did scientists originally think proteins carried hereditary information?

A: Proteins have 20 amino acids → huge variety. DNA has only 4 bases, seemed too simple.

Q: What did Griffith’s experiment discover?

A: Bacterial transformation—something in dead S cells turned R cells into virulent S cells.

Q: Did Griffith discover that DNA was the genetic material?

A: No. He discovered transformation but didn’t know the molecule responsible.

Q: What question were Hershey & Chase trying to answer?

A: Whether DNA or protein is the genetic material in viruses.

Q: What radioactive element labels proteins in the Hershey–Chase experiment?

A: ³⁵S (sulfur) — proteins contain sulfur.

Q: What radioactive element labels DNA in the Hershey–Chase experiment?

A: ³²P (phosphorus) — DNA contains phosphorus.

Q: What did Hershey & Chase conclude?

A: DNA enters the cell and directs viral replication → DNA is the genetic material.

Q: What did Chargaff discover about DNA composition across species?

A: DNA varies between species — disproved the idea that DNA is too simple.

Q: Chargaff’s Rule #1?

A: %A = %T and %G = %C.

Q: Chargaff’s Rule #2?

A: DNA composition differs across species.

Q: What technique did Rosalind Franklin use to study DNA?

A: X-ray crystallography.

Q: What did Photo 51 reveal?

A: DNA is a double helix with uniform width and phosphates on the outside.

Q: Watson & Crick’s major contribution?

A: Built the double helix model based on existing data.

Q: What does antiparallel mean in DNA?

A: The two strands run in opposite directions: 5’→3’ and 3’→5’.

Q: Why does a purine always pair with a pyrimidine?

A: Maintains consistent width of the DNA helix.

Q: Which bases are purines?

A: A and G (two rings).

Q: Which bases are pyrimidines?

A: C and T (one ring).

Q: How many hydrogen bonds between A and T?

A: 2 (“A–T–2”).

Q: How many hydrogen bonds between C and G?

A: 3 (“C–G–3”).

Q: Where are sugar and phosphate located in DNA?

A: On the outside forming the backbone.

Q: Where are nitrogenous bases located?

A: On the inside, paired through H-bonds.

Q: What is the term for DNA being copied before cell division?

A: DNA replication (structure reveals the mechanism).

Q: Who got the Nobel Prize for the DNA model?

A: Watson, Crick, and Wilkins (Franklin did not).