6.9.3 Eukaryotic Genomic Organization: Gene Families

Question 1

note

Answer 1

• Repetitive DNA consists of nucleotide sequences that do not code for protein products. Tandemly repetitive
  DNA is commonly found within centromeres and telomeres.

Question 2

gene families

Answer 2

• are repeating DNA sequences that code for identical or very similar RNA products, located close together
  on a chromosome. Three examples of gene families include the Alu gene family, ribosomal RNA gene families, and the globin gene families.
  · One example is the Alu gene family. Multiple copies of the gene, each 300 base pairs long, transcribe for an RNA molecule.
  · Another example is the gene family coding for rRNA. It makes sense that the gene is present in multiple copies since the cell has a high demand for ribosomal RNA.

Question 3

Illustration of the gene family for ribosomal RNA.

Answer 3

1) The strand at the top of the illustration is the DNA template that codes for the rRNA gene family.
2) A strand of messenger RNA is transcribed (the second strand in the illustration). The RNA transcript contains related genes coding for rRNA. The copies are separated by noncoding spacer sequences.
3) RNA processing yields three rRNA mole- cules: 18S, 5.8S, and 28S. (The S strands for their respective sedimentation rates in an ultracentrifuge. Larger molecules sediment at slower speeds.)

Question 4

Telomeres consisting of tandem repeats

Answer 4

• are essential to a functioning chromosome.
• help prevent the chromosome from losing genes during replication.
• prevent the ends of the chromosome from binding to other chromosomes.

Question 5

The presence of tandem repeating DNA in telomeres and centromeres suggests that these sequences

Answer 5

• play a structural role in the chromosome

Question 6

Groups of similar interspersed DNA repeats are

Answer 6

• gene families.

Question 7

A multi-gene family

i. is a collection of similar or identical genes.
ii. is defined by the function of the encoded proteins rather than the similarity of the DNA sequences.
iii. consists of short repetitive DNA sequences.
iv. may arise from repeated gene duplication
v. is responsible for the production of globins, the subunits of hemoglobin.

Answer 7

• i, iv, v

Question 8

One gene family is called Alu elements. Which of the following is not true of these elements?

Answer 8

• They are named for the human disease they cause