1. What are the four types of nucleotides that make up DNA and how do

they pair up to form the double helix? (2 points)

Answer: The four types of nucleotides are adenine (A), thymine (T),

cytosine (C), and guanine (G). They pair up according to the

complementary base pairing rule: A with T and C with G. The two strands

of DNA are held together by hydrogen bonds between the paired bases.

Rationale: This question tests the basic knowledge of the structure and

composition of DNA, which is the main genetic material in humans.

2. What is the difference between a gene and an allele? (2 points)

Answer: A gene is a segment of DNA that codes for a specific protein or

trait. An allele is a variant form of a gene that may have different effects

on the phenotype. For example, the gene for blood type has three alleles:

A, B, and O.

Rationale: This question tests the understanding of the concepts of gene

and allele, which are important for studying inheritance and variation.

3. What is the difference between genotype and phenotype? (2 points)

Answer: Genotype is the genetic makeup of an individual, which

determines the potential traits that can be expressed. Phenotype is the

actual physical appearance or expression of the traits, which may be

influenced by environmental factors. For example, a person may have the

genotype for brown eyes (BB) but have blue eyes as a phenotype due to a