Gene and Chromosomal Mutations

Question 1

What are the two types of mutations in multicellular organisms?

Answer 1

1. Germline mutations
   
   • May be transmitted to offspring and to successive generations
2. Somatic mutations
   
   • Not inherited by the progeny

Question 2

What are the 2 basic types of changes to a gene in Gene/point mutation

Answer 2

1. Nucleotide Substitution
2. Nucleotide Insertion or deletion
   
   • If not in multiples of 3s may result in Frameshift mutation, resulting in extensive missense mutation.

Question 3

Describe a missense mutation

Answer 3

A nucleotide substitution in a DNA sequence changes the mRNA codon. This results in the translation of a different amino acid.

Amino acid sequence of the polypeptide is changed, causing change in the specific 3d-conformation of the protein, altering its function.

Question 4

Describe a nonsense mutation

Answer 4

• Nucleotide sub in a DNA sequence changes a codon for an amino acid into a stop codon.
• Premature termination of translation, the resulting polypeptide will be shorter (truncated) than the normal polypeptide encoded.
• Amino acid sequence of the polypeptide is shortened, causing change in the specific 3d-conformation of the protein, altering its function.
• Nearly all result in non-functional proteins

Question 5

Describe a silent mutation

Answer 5

• Nucleotide sub in a DNA sequence changes the mRNA codon. However, same amino acid inserted into the polypeptide because of the degeneracy of the genetic code.
• Amino acid sequence of the polypeptide is unchanged, causing no change in the specific 3d-conformation of the protein, NOT altering its function.

Question 6

Describe a neutral mutation

Answer 6

• Nucleotide sub in a DNA sequence changes the mRNA codon. Resulting amino acid produces not detectable change in the function of the protein translated
• Could be original amino acid replaced with one of similar physical and chemical properties
• Could be that amino acid residue substituted is non-essential to that protein’s structure and function
• Amino acid sequence of the polypeptide is changed, but there is no change in the specific 3d-conformation of the protein, NOT altering its function.

Question 7

What gene is mutated in sickle-cell anaemia?

Answer 7

Beta symbol-golbin gene which encodes on of the polypeptide subunits that make up haemoglobin (Hb)

Question 8

Describe genetic alteration caused by sickle-cell anaemia

Answer 8

• Subs of a thymine for an adenine at one postion in the Hb gene (template strand), which results in a missense mutation.
• Sixth amino acid residue in polypeptide is changed from a glutamate (hydrophilic) to a valine (hydrophobic).

Question 9

Describe the molecular alteration caused by sickle-cell anaemia

Hint: five points

Answer 9

• Specific 3d-conformation and function of Hb protein is altered.
• Substitution creates a hydrophobic spot on the outside of the Hb protein that sticks to the hydrophobic region of an adjacent Hb protein’s beta chain
• The mutant Hb subunits tend to stick to one another when the oxygen concentration is low, particularly when red blood cells are in capillaries and veins
• The aggregated proteins form fibre-like structures within red blood cells.
• At high oxygen concentration, haemoglobin resumes globular haemoglobin structure.

Question 10

Describe the physiological effects of sickle-cell anaemia

Answer 10

• The fibre like structure causes the red blood cells to lose their normal morphology and become sickle-shaped. Sickled cells are less able to move through capillaries and can block blood flow, resulting in severe pain and cell death of the surrounding tissue due to shortage in oxygen.
• Sickled rbcs are also fragile and easily destroyed, further decreasing the oxygen carrying capacity of blood

Question 11

What is the term for production of mutations

Answer 11

Mutagenesis

Question 12

What is chromosomal aberration?

Answer 12

1. A change in the structure of chromosome

2. A change in the number of chromosomes

Question 13

What are the four types of chromosomal abberation?

Answer 13

1. Deletion
2. Duplication
3. Inversion
4. Translocation

Question 14

Describe deletion

Answer 14

When a chromosome breaks in one or more places, and a portion of it is lost, the missing piece is referred to as deletion.

This can occur near one end or from the interior of the chromosome. These are called terminal or intercalary deletions respectively.

Question 15

Effects of deletion

Answer 15

• Genotype is altered due to absence of certain gene loci, having a profound effect
• If a deletion affects the same gene loci on both homologous chromosomes, the effect is usually lethal.
• IF only one of a homologous chromosomes if affected, the effect on the phenotype is that alleles on the non-deficient homologue will be expressed, even if recessive

Question 16

Describe duplication

Answer 16

When any part of the genetic material (be it single locus or large piece of chromosome) is present more than once in the genome, it is called duplication.

Duplication can arise as a result of :

1. Unequal crossing over between synapsed chromosomes during meiosis (deletion also happens)
2. Through a replication error prior to meiosis

Question 17

Effects of duplication

Answer 17

Gene redundancy and phenotypic variations.

Also an important source of genetic variation during evolution.