DNA Variants

Question 1

How do DNA, RNA and Proteins link together?

Answer 1

DNA codes for RNA which codes for a protein

Question 2

What is the Primary Transcript?

Answer 2

First RNA produced (still contains the introns)

Question 3

How can a single nucleotide variant result in a disease being caused?

Answer 3

Changes wild type variant into a stop codon, hence a disease being caused/developed

Question 4

What is a mis-sense variation?

Answer 4

Single nucleotide results in codon coding for a different amino acid (NFP or no effect)

Question 5

What is a Trinucleotide repeat?

Answer 5

Repetitive DNA sequence of 3 nucleotides (Dangerous in large quantities)

Question 6

What does a deletion variation cause?

Answer 6

Frameshift (result in frameshift further down)

Question 7

What is an in-frame deletion?

Answer 7

Whole Amino Acid removed (varying effects)

Question 8

What is a splice-site variant?

Answer 8

Affects accurate removal of an intron

Question 9

What is a non-sense variant and effect?

Answer 9

Codon changed to a stop, RNA detaches from ribosome and degraded (incomplete/NFP)

Question 10

What do more repeats in triplet repeat signify?

Answer 10

A greater severity of disease caused by repeats

Question 11

2 types of heterogeneity?

Answer 11

1) Allelic: Lots of different variants in one gene

2) Locus: Variants in different genes give same clinical condition

Question 12

Difference between D and R variants?

Answer 12

Dominant manifest disease phenotype in heterozygous state (D-ve where variant interferes with protein from normal)

Question 13

2 function variants?

Answer 13

1) Loss: Only one allele functioning (Recessive mostly)

2) Gain: Increased gene dosage and protein activity

Question 14

Types of screening (2)?

Answer 14

1) Biochemical: Currently most accurate

2) Genetic: Eventually replace biochemical as technology develops and improves

Question 15

What variant would a stop codon be classed as?

Answer 15

Non-sense variant

Question 16

Summarise autosomal dominant inheritance. (4)

Answer 16

• Manifests in the heterozygous state.
• Male to Male transmission is seen.
• Both males and females are affected equally.
• The disease is present in several generations.
• There is a 50% chance of offspring having the disease.

Question 17

Summarise autosomal recessive inheritance. (4-5)

Answer 17

• Manifests in the homozygous state.
• The disease is often not seen in every generation.
• 25% chance of offspring having the disease.
• 50% chance of offspring being carriers.
• Healthy siblings have a 2/3 chance of being carriers.