Chapter 3.1 Genes

Question 1

Gene

Answer 1

A gene is a inheritable factor which consists of a length of DNA molecule and occupies a specific location (locus) on a chromosome. It determines a specific physical characteristic of an organism.

Question 2

Example of a characteristic being determined by multiple alleles

Answer 2

ABO blood group

Question 3

Chromosomes in eukaryotes

Answer 3

Are structural units made up of supercoiled DNA molecules and histone proteins.

Question 4

For individuals of the same species

Answer 4

Same number of chromosomes

Same genes at the same loci

Question 5

What are the main aims of the Human Genome Project

Answer 5

Discover and sequence the complete set of human genes and make the research results available for furture biological studies (e.g. treating genetic diseases).

Question 6

Genome

Answer 6

The whole of the genetic information possessed by an organism.

Question 7

What technological advancements allowed DNA sequencing to be carried out faster and cheaper?

Answer 7

Laser –> fluoresce the dye markers
Digital camera –> reading the dye marker banding patterns
Cumputer –> automate the sequencing process
PCR –> amplify DNA fragments
Fluorescent labeling technique –> allows 4 nucleotides to be analyzed at the same time

Question 8

Base-substitution mutation

Answer 8

A permenant change in the DNA sequence where the right bases are substituted by the wrong ones due to errors during transcription. The chances of mutation can be increased due to higher exposures to mutagens.

Question 9

Three types of base-substitution mutation

Answer 9

1. Silent: does not cause any changes to the AA produced
2. Missense: causes a different AA to be produced (e.g. sickle-cell anemia)
3. Nonsense: causes a stop AA to be produced –> the polypeptide is shortened

Question 10

Describe the causes of sickle-cell anemia

Answer 10

Caused by a single base-substitution mutation in the HBB gene on chromosome 11.
Valine is produced instead of glutamine (glutamic acid, which is polar) from the mRNA transcribed from the mutation-carrying DNA.
Valine (which is non-polar) in hemoglobin causes them to stick together and form rigid bundles in tissues with low O2 concentration –> distort the round disc shape of RBCs into sickle-shaped.
The sickle cells trap in blood vessels, blocking them and causes damage to the vessels and reduces blood flow –> anemia.
Also, the lifetime of RBCs are shortened to 4 days, because when RBCs are continuously being distorted into sickle shape and return to its regular shape in tissues with high O2 concentration (e.g. lungs), both blood vessels and hemoglobin (RBCs) itself are damaged.
The patient usually cannot replace RBCs at a rapid enough rate –> lower RBCs concentration –> anemia.

Question 11

Malaria

Answer 11

Caused by a plasmodium cell and transferred/spread by mosquitos.
The plasmodium cell invades normal RBCs and cause them to lyse.

Question 12

Symptoms of malaria

Answer 12

Fever, shivering, anemia, vomiting

Death is common, usually due to kidney failure/severe anemia.

Question 13

Malaria as a selective advantage

Answer 13

Malaria-causing plasmodium cells cannot invade sickle cells –> people HETEROzygous of sickle-cell anemia are resistant to malaria.

Selective/survival advantage in areas where malaris is epidemic (e.g. southeastern Asia, middle Africa, northern areas in North America).

Question 14

Number of genes in humans, grapes, and chicken.

Answer 14

Chicken: 17,000
Human: 23,000
Grape: 30,000

Question 15

Where can the sickle-cell mutation be found on the HBB gene? And the base sequence in question?

Answer 15

Sixth amino acid (valine glutamic acid)
DNA: GAG becomes GTG
mRNA: GAG becomes GUG