Question 1

Which of the following statements best explains why humans can produce many more polypeptides than the number of genes in their genome?

Accepted Answer

Alternative splicing of RNA transcripts allows a single gene to code for multiple polypeptides.

Question 2

Based on Table 18.1, which organism has the highest gene density (genes per Mb)?

Accepted Answer

Archaeoglobus fulgidus

Question 3

If the haploid genome size of Escherichia coli is 4.6 Mb and it contains 4,400 genes, what is the gene density (genes per Mb)?

Accepted Answer

950 genes per Mb

Question 4

Which of the following best describes the relationship between genome size and organism complexity?

Accepted Answer

There is no systematic relationship between genome size and phenotype complexity.

Question 5

What is the main reason why vertebrate genomes can 'get more bang for their buck' from their coding sequences?

Accepted Answer

They utilize alternative splicing, producing multiple proteins from a single gene.

Question 6

Which organism listed in Table 18.1 has the lowest gene density?

Accepted Answer

Homo sapiens

Question 7

Given that the giant panda (Ailuropoda melanoleuca) has a haploid genome size of 2,400 Mb and 21,000 genes, calculate its gene density.

Accepted Answer

$$\frac{21,000}{2,400} = 8.75$$ genes per Mb

Question 8

Which of the following is a characteristic of prokaryotic genomes compared to eukaryotic genomes?

Accepted Answer

Prokaryotic genomes have higher gene density and less noncoding DNA.

Question 9

Which process is primarily responsible for the discrepancy between the number of genes and the number of polypeptides produced in human cells?

Accepted Answer

Alternative splicing

Question 10

What is the significance of noncoding DNA in eukaryotic genomes?

Accepted Answer

It includes regulatory sequences and introns, contributing to gene regulation and complexity.

Question 11

If a eukaryotic organism has a genome size of 120 Mb and 27,000 genes, what is its gene density?

Accepted Answer

$$\frac{27,000}{120} = 225$$ genes per Mb

Question 12

Which of the following best describes the DNA content of most multicellular eukaryotes?

Accepted Answer

Most of their DNA is noncoding and includes regulatory sequences and introns.

Question 13

Why do some scientists believe that the added level of regulation from noncoding DNA may contribute to greater organismal complexity?

Accepted Answer

Noncoding DNA allows for more sophisticated gene regulation and expression.

Question 14

Which organism in Table 18.1 has the largest haploid genome size?

Accepted Answer

Ailuropoda melanoleuca

Question 15

What is the best estimate for the number of genes in the human genome?

Accepted Answer

About 20,000

Question 16

Which of the following is NOT a plausible explanation for why eukaryotes have fewer genes per Mb than prokaryotes?

Accepted Answer

Eukaryotes have higher gene density.

Question 17

Which of the following best describes the content of bacterial genomes?

Accepted Answer

Most of the DNA codes for proteins, tRNA, or rRNA.

Question 18

If Zea mays (corn) has a genome size of 2,300 Mb and 32,000 genes, what is its gene density?

Accepted Answer

$$\frac{32,000}{2,300} = 13.91$$ genes per Mb

Question 19

Which of the following is a major theme regarding genome size and gene number in eukaryotes?

Accepted Answer

There is no systematic relationship between genome size and gene number.

Genome Size, Gene Number, and Gene Density in Prokaryotes and Eukaryotes

Study Guide - Practice Questions